Designing Safe General LED Lighting That Provides the UVB Benefits Of

Article Designing Safe General LED Lighting that Provides the UVB Beneﬁts of Sunlight

Seung-Taek Oh 1, Dae-Hwan Park 2 and Jae-Hyun Lim 2,*

1 Smart Natural Space Research Center, Kongju National University, Chungcheongnam-do 31080, Korea; [email protected] 2 Dept. of Computer Science & Engineering, Kongju National Uiniversity, Cheonan-si, Chungcheongnam-do 31080, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-41-521-9558

Received: 9 January 2019; Accepted: 25 February 2019; Published: 26 February 2019

Abstract: The ultraviolet (UV) rays emitted from sunlight greatly influence human health. Excessive exposure to UV rays can be harmful to eyes and skin; however, limited UVB exposure is essential for the synthesis of vitamin D. Nowadays, owing to insufficient exposure to natural light, there is increasing concerns about low vitamin D amongst individuals. To address this issue, many lighting devices that provide UVB doses have been released; however, such devices are only used for treatments or for special purposes. This study proposes a general indoor lighting system with a UVB LED light source to provide safe UVB doses to users who spend large amounts of time indoors. The optical characteristics of two UVB LEDs with output of 20 and 100 mW were analyzed based on their distances and applied currents. The light source combination of UVB LEDS that meets the UV hazard standard of IEC-62471 was derived; this is a photobiological safety evaluation standard of LED lighting devices. We then produced a lighting module in which the UVB LED light source was applied to general LED lighting and measured and analyzed the spectral irradiance of the proposed lighting according to the measurement standard for the general lighting of IEC 62471. The actinic UV hazard (AUV) and near-UV hazard (NUV) were calculated to be 0.001 and 10 W/m2, respectively. Thus, the provision of UVB dose did not pose any risks. In addition, the total EUV (Erythemal weighted UV) dose when the proposed lighting was implemented for 16 h was 187.66 J/m2, confirming that this dose did not cause erythema for the general skin types (Skin Types 1–6). Further, the design plan of general indoor lighting with a UVB LED light source is presented.

Keywords: UVB; UVB LED general lighting; UV safety evaluation; general lighting design; UVB characteristics of sunlight

1. Introduction Ultraviolet (UV) rays are electromagnetic waves of 200–400 nm wavelength bands comprising UVA (315–400 nm), UVB (280–315 nm), and UVC (200–280 nm) [1]. Of these, the UVC and most UVB rays are absorbed into the ozone layer, and 10–30% of UVB and UVA, respectively, reach the earth’s surface and affect humans [2]. Excessively exposure to UV radiation causes a harmful effect on the human body. UVA promotes aging on the skin, while UVB can cause skin cancer [3,4]. Any wavelength lower than 315 nm has negative effects on the eyes, causing inflammation of the cornea or cataract [5]. However, adequate exposure to UVB is beneficial for human health as it assists in the synthesis of vitamin D and promotes mental health [6]. UV of sunlight can be harmful or beneficial depending on the degree of exposure [7], and issues on deterioration of health, such as vitamin D deficiency due to a lack of exposure to natural light, have been raised recently [8,9]. Vitamin D deficiency causes rickets, osteomalacia, and hypotonia and increases the risk of developing diabetes, hypertension,

Appl. Sci. 2019, 9, 826; doi:10.3390/app9050826 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 826 2 of 12 and myocardial infarction [10,11]. Therefore, vitamin D is essential for human health. Studies have introduced several ways to supplement vitamin D [12–14]. Vitamin D in the body is produced through ingestion of food and supplements, or skin exposure to UVB. However, vitamin D supplementation through diet has been reported to be limited [12,13,15]. Even though one steadily ingests foods beneficial to produce vitamin D, such as milk and salmon, or vitamin D supplements, vitamin D deficiency is still found [16]. Meanwhile, since sunlight can support vitamin D production even with a short exposure to it [15,17], exposure to the UVB of the sunlight is suggested as the most effective method of meeting the vitamin D requirements [14]. However, many people stay indoors for an average of 85–90% a day [18], and some of the countries in the northern hemisphere, such as the USA and European countries, are raising the issue of a shortage of sunlight due to geographic factors. In many cases, the decrease of outdoor activities is caused by an averting behavior caused by the deterioration of air quality due to fine dust or smog. In the United States, when the air quality index (AQI) is high, the outdoor activity time is reduced by 18%—among the elderly, by 59% [19,20]. In Korea, an alert service is operated to encourage people to refrain from outdoor activities when the concentration of fine dust is high [21]. Therefore, natural light cannot completely satisfy the required UVB dose. To address this issue, UVB irradiation devices that artificially provide adequate UVB doses have been proposed [22]. However, such UVB irradiation devices are limited by the fact that there are special lightings to which certain parts of the body must be exposed at certain distances and are used for treatments with limited uses [23]. Specialized lighting for treatment does not provide natural UVB light in daily life like sunlight because users must consciously use instruments after spending money and time. Therefore, there is a lack of research on the development of general lighting that provides UVB for human health for people who are not frequently exposed to natural light. Recently, LED light sources capable of providing various optical characteristics of UV and IR and the visible light characteristics of natural light have been developed. Although LEDs are a low-power, high-efficiency light source with a high manufacturing cost, various optical characteristics can be reproduced via output control for industrial applications [24,25]. Several lighting devices employ LED, such as light-therapy facemasks, those found in plant factory and micro algae cultivation facilities, and lighting devices for sterilization and environmental purification using UV LEDS [26]. Owing to these devices, the concern about the harmfulness of lighting devices to the human body has increased. Therefore, the International Electrotechnical Commission (IEC) introduced IEC 62471, a standard for the photobiological safety evaluation of lighting: in Europe, all lighting devices must display their own IEC-based hazard rating [27,28]. The hazard level of UV-based devices was evaluated based on the IEC 62471 standard for safe use [29]. This study proposes a design plan for indoor lighting that can provide the UVB dose safely to indoor users using a UVB LED light source that can control the current output. The optical characteristics of two types of UVB LED light sources of 20 and 100 mW output specifications were measured and analyzed, respectively, based on their distances from the lighting source and applied current. In the analysis process, the actinic UV hazard radiation (AUV, 200~400 nm) and near-UV hazard radiation (NUV, 315~400 nm) values that are used to determine the UV hazard level based on IEC 62471 were calculated; then, a combination of light sources that enables safe UVB radiation was derived. Finally, in order to support the synthesis of vitamin D, we produced a general lighting module in which UVB LEDs added to general (visible) LEDs was manufactured and measured, and the spectral irradiance in the lighting box shielded from external light was analyzed. After confirming whether the proposed lighting causes erythema on human skin, it was verified whether the UV hazard standard of IEC 62471 was followed. The UVB characteristics of sunlight were reproduced via this method, and a development plan for safe, general indoor lighting that enables vitamin D synthesis is suggested. Appl. Sci. 2019, 9, 826 3 of 12

2. Methods: UVB Characteristics of Natural Light Appl. Sci. 2018, 8, x 3 of 11 Appl. Sci.UVA 2018 and, 8, x UVB are components of UV rays that have different levels of effects on the human3 of 11 body [30]. The local solar UV irradiance was measured and analyzed to provide a typical solar irradiance usedirradiance to calculate used UV to calculateexposure. UV Measurements exposure. Measurements were taken at were a latitude taken ofat a36.85 latitude and ofa 36.85 and a irradiance used to calculate UV exposure. Measurements were taken at a latitude of 36.85 and a longitude of 127.15longitude on the of 127.15roof of on a 10-story the roof buildof a 10-storying to minimize building shadow to minimize interference. shadow Theinterference. spectral The spectral longitude of 127.15 on the roof of a 10-story building to minimize shadow interference. The spectral irradiance wasirradiance measured was at noon measured on a clear at noon day on in summera clear day since in summer it would since be advantageous it would be advantageous to identify to identify irradiance was measured at noon on a clear day in summer since it would be advantageous to identify the characteristicsthe characteristics of UV light under of UV strong light undersunlight. strong The sunmeasurementlight. The measurement was conducted was on conducted 21 July on 21 July the characteristics of UV light under strong sunlight. The measurement was conducted on 21 July 2018, 2018, and the 2018,concentrations and the concentrations of the fine dust of werethe fine 76 μdustg/m were3 for pm1076 μg/m and3 for 50 pm10μg/m3 andfor pm25,50 μg/m which3 for pm25, which and the concentrations of the ﬁne dust were 76 µg/m3 for pm10 and 50 µg/m3 for pm25, which are are “normal” arelevels “normal” (according levels to (accordingthe Korea Meteorto the Koreaological Meteor Administration).ological Administration). A spectrometer A spectrometer(CAS (CAS “normal” levels (according to the Korea Meteorological Administration). A spectrometer (CAS 140CT 140CT 152) capable140CT of152) measuring capable of spectral measuring irradiance spectral in irradiancethe range ofin 200–800the range nm of was200–800 used nm as thewas used as the 152) capable of measuring spectral irradiance in the range of 200–800 nm was used as the measuring measuring instrument.measuring Its instrument. specifications Its specifications are shown in Tableare shown 1. In addition,in Table 1. the In resultsaddition, of thethe measuredresults of the measured instrument. Its speciﬁcations are shown in Table1. In addition, the results of the measured natural natural light arenatural shown light in areFigure shown 1. in Figure 1. light are shown in Figure1.

Table 1. SpecificationsTable 1. of Specifications the spectrometer of the (CAS spec trometer140CT 152). (CAS 140CT 152). Table 1. Speciﬁcations of the spectrometer (CAS 140CT 152). Spectral SpectralNumber ResolutionNumber Resolution Model (Company)Model (Company) Image Image Model (Company) ImageRange[nm] Spectral RangeRange[nm]of Pixels [nm] Numberof[nm] Pixels of Pixels[nm] Resolution [nm] CAS140CTCAS140CT 152 CAS140CT 152 (Instrument(Instrument (Instrument 200–800 200–800 1024200–800 × 768 1024 1024 2.7 × 768× 768 2.7 2.7 Systems) Systems) Systems)

Figure 1. CharacteristicsFigure 1. Characteristicsof sunlight by wavelength. of sunlight by wavelength.

The sunlight characteristicsThe sunlight characteristics based on the measured based on the results measured are shown results in Figureare shown 1. We in calculated Figure1 1.. WeWe calculated calculated the total irradiancethethe totaltotal of irradianceirradiancesunlight, UVA, of of sunlight, sunlight, and UVB UVA, UVA, irradiance and and UVB UVB using irradiance irradiance Equation using using (1). Equation EquationErythemal (1). (1). Erythemal weighted Erythemal weighted weighted UV UV radiationradiationUV (EUV), radiation which (EUV), (EUV), is which UV whichradiation is UV is radiation UV that radiation produces that produces that erythema produces erythema at aerythema atgiven a given wavelength, at wavelength, a given waswavelength, was calculated was calculated usingusingcalculated Equation Equation using (2). (2). EquationEUV EUV is a is (2).weighted a weighted EUV is measure a measureweighted of the of measure the likelihood likelihood of the of likelihooderythema, of erythema, ofa type erythema, a type of of skin a type burn of skin burn occurringoccurringskin burn in the inoccurring the UV UV wavelength wavelength in the UV band, wavelength band, which which isband, isneeded needed which to to calculate is calculate needed safe safeto calculatelevels levels of of exposuresafe exposure levels to of ultraviolet exposure to ultraviolet lightto ultraviolet and to calculate calculate light and the the to amount calculate amount of of the vitamin vitamin amount D D synthesisof synthesis vitamin [14]. [D14 synthesis ].At At this this time, [14]. time, the At the erythemathis erythema time, the weighting erythema weighting functionfunctionweighting (S (Ser )er functionof) of Equation Equation (Ser) (3)of (3) Equation was appliedapplied (3) accordingwasaccording applied to to the accordingthe deﬁnition definition to of the Commissionof definitionCommission Internationale of Commission de InternationaleI’EclairageInternationale de I’Eclairage (CIE) de (CIE) [ 31I’Ec,32 [31,32].lairage]. (CIE) [31,32]. UVA = 𝐸𝜆𝑑𝜆UVAZ (W/m =400 )𝐸𝜆𝑑𝜆, UVB (W/m = ),𝐸𝜆𝑑𝜆 UVB (W/m =Z 315 )𝐸𝜆𝑑𝜆 (W/m) (1) (1) UVA = Eλdλ W/m2, UVB = Eλdλ W/m2 (1) 315 280 EUV = 𝐸𝜆𝑆𝑑𝜆 (W/m ) ,EUVA= 𝐸𝜆𝑆𝑑𝜆 (W/m ), EUVB = 𝐸𝜆𝑆𝑑𝜆 (W/m ) EUV = 𝐸𝜆𝑆𝑑𝜆 (W/m) ,EUVA= 𝐸𝜆𝑆𝑑𝜆 (W/m), EUVB = 𝐸𝜆𝑆𝑑𝜆(2) (W/m ) (2) R 400 2 R 400 2 R 315 2 EUV = 280 EλSerdλ W/m , EUVA = 315 EλSerdλ W/m , EUVB = 280 EλSerdλ W/m (2) 1 (250 ≤ 𝜆1 ≤ (250298) ≤ 𝜆 ≤ 298) 𝑆 (𝜆) = 10.() (298.() ≤ 𝜆 ≤ 328) λ: Wavelength[nm] 𝑆(𝜆) = 10 (298, ( ≤ 𝜆 ≤ 328), (λ: Wavelength[nm]). ). (3) (3) .() 10 (32810.( ≤ 𝜆 ≤) (328400) ≤ 𝜆 ≤ 400)

Thus, the totalThus, irradiance the total was irradiance 547.3 W/m was2, of547.3 which W/m UVA2, of andwhich UVB UVA were and 47.7 UVB and were 1.4 W/m47.7 2and, 1.4 W/m2, respectively, accountingrespectively, for accounting 8.71% and for 0.26% 8.71% of andthe total0.26% irradiance; of the total thus, irradiance; the spectral thus, irradiance the spectral of irradiance of UVA was 35 UVAtimes was higher 35 timesthan UVB.higher However, than UVB. th eHowever, results of th applyinge results theof applyingerythema the weighting erythema weighting function werefunction 0.05 and were 0.15 0.05W/m and2 for 0.15 EUVA W/m and2 for EUVB, EUVA respectively. and EUVB, Thus,respectively. EUVB wasThus, three EUVB times was three times higher than EUVA,higher andthan UVB EUVA, had and a considerable UVB had a considerableeffect on the effecthuman on body the humancompared body with compared UVA. with UVA. Appl. Sci. 2019, 9, 826 4 of 12

  1 (250 ≤ λ ≤ 298)  0.094(298−λ) Ser(λ) = 10 (298 ≤ λ ≤ 328) , (λ : Wavelength[nm]). (3)   100.015(140−λ) (328 ≤ λ ≤ 400)

Thus, the total irradiance was 547.3 W/m2, of which UVA and UVB were 47.7 and 1.4 W/m2, respectively, accounting for 8.71% and 0.26% of the total irradiance; thus, the spectral irradiance of UVA was 35 times higher than UVB. However, the results of applying the erythema weighting function were 0.05 and 0.15 W/m2 for EUVA and EUVB, respectively. Thus, EUVB was three times higher than EUVA, and UVB had a considerable effect on the human body compared with UVA. EUV was 0.2 W/m2, which can cause erythema upon exposure for longer than 25 min if the person has a skin color of beige to light brown [33]. A previous study revealed that Asians (Koreans) could produce 200 IU of vitamin D when exposed to an EUVB intensity of 0.15 W/m2 for ~12 min (720 s) [34]. Therefore, in order to support more than 200 IU of vitamin D synthesis through lighting, EUVB doses greater than 0.15 W/m2 × 720 s = 108 J/m2 (Joule = Watt × Time [35]) could be provided to skin types commonly found in the Asian region.

3. Methods: UVB LED General Lighting Design

3.1. UV Safety Evaluation Excessive exposure to the UV rays can cause erythema, which is a kind of skin burn [36], and UV can be harmful to the human body even if a person is exposed to the UV at a lower level continuously [7]. Therefore, the UVB-LED general lighting proposed in this paper provides a UVB intensity of light at a level that would not cause erythema, meeting the safety evaluation standard (IEC 62471) for lighting devices. The IEC has established the IEC 62471 standard to evaluate the photobiological safety of lighting devices using LED light sources [37]. Therein, the hazards caused to eyes and skin due to lighting are divided into the following eight categories: eye and skin photochemistry UV, eye UVA, retinal blue light, retinal blue light with a small light source, retinal heat, retinal heat caused by weak visual stimulus, eye IR, and skin heat. Each item is classified and marked by four categories, namely, the exclusion group, the low-risk group, the moderate-risk group, and the high-risk group, after analyzing spectral irradiance and radiance measured by wavelength range. IEC 62471 also classifies lighting into a general lamp service (GLS) and other lamps, and applies different test methods accordingly. In this case, GLS refers to general lighting used at homes or offices, and other lamps, excluding GLS, are those used for industrial or medical lighting devices used for suntan, water purification facilities, and medical treatments [23]. Depending on the type of lamps used, the optical characteristics of the GLS are measured with a 500-lux brightness. We further evaluated whether a hazard caused by the UVB dose existed. At this time, the hazard assessment based on the UVB light source is limited to an actinic UV hazard (AUV) and a near-UV hazard (NUV). Details of emission limits for each item are summarized in Table2[37].

Table 2. IEC 62471 classiﬁcation standard for ultraviolet (UV) risk items.

Hazard Items Unit Exempt Risk Group 1 Risk Group 2 Actinic ultraviolet hazard (AUV) W/m2 0.001 0.003 0.03 Near-UV hazard (NUV) W/m2 10 33 100

Exempt is the safest lamp rating in Table1, and its radiation in each item of AUV is 0.001 W/m 2. NUV is applied when Exempt ≤ 10 W/m2. AUV is calculated by integrating the AUV hazard Appl. Sci. 2019, 9, 826 5 of 12

weighting function (SUV) to the spectral irradiance of 200–400 nm wavelength band (Equation (4)); NUV was calculated by integrating the spectral irradiance of 315–400 nm UVA wavelength band.

Z 400 AUV = E(λ)SUV (λ)dλ (4) 200 where λ = wavelength, E(λ) = UV spectral irradiance, and SUV (λ) = actinic ultraviolet hazard weighting function. In this case, the AUV hazard weighting function (SUV) uses the weight table value by wavelength according to IEC 62471 [28]. When no reference value for the observed spectral wavelength is available, 0 a weighted value based on each wavelength is calculated by linear interpolation, as shown by S UV (λ) in Equation (5).

0 SUV (λr) − SUV (λl) S UV (λ) = SUV (λl) + (λ − λl) , (λl < λ < λr). (5) Appl. Sci. 2018, 8, x λr − λl 5 of 11

Equations (6) and (7) are the ﬁnal formulas of AUV and NUV, respectively. AUV =400 𝐸(𝜆)𝑆 (𝜆)Δ𝜆 (6) 0 AUV = ∑E(λ)S UV (λ)∆λ (6) λ=200 NUV =Z 400 𝐸(𝜆)𝑑𝜆Z =400 𝐸(𝜆)Δ𝜆 . (7) NUV = E(λ)dλ = E(λ)∆λ. (7) 315 315

3.2. Overall Overall Lighting Design Using the UVB LED LED Light Light Source IEC 62471 states that the stability evaluation of of general lighting must must be measured at an illuminanceilluminance of 500 500 lux lux [27]. [27]. Further, Further, considering considering that that the the average average ceiling ceiling height height of of houses, houses, apartments, apartments, and ofﬁcesoffices areare 2.4–2.8 2.4–2.8 m, m, general general lighting lighting should should be able be able to provide to provide a brightness a brightness of 500 luxof 500 at a distancelux at a distanceof 1.5 m. of To 1.5 this m. end, To this white end, multi-channel white multi-channel LEDs are LEDs used are for used such for purposes. such purposes. UVB LED UVB light LED sources light sourceswere utilized were toutilized provide to UVBprovide doses UVB that doses are beneﬁcial that are beneficial to the human to the body. human LEDs body. can controlLEDs can the control optical thecharacteristics optical characteristics by adjusting by the adjusting applied current the applied output. current LED light output. sources LED may light be combinedsources may to form be combinedvarious types to form of lighting. various Based typeson of theselighting. characteristics, Based on these to control characteristics, all LED light to control sources, all a LED controller light sources,was developed a controller so that was the desireddeveloped brightness so that andthe thedesired UVB dosebrightness could beand achieved. the UVB Figure dose2 couldoutlines be achieved.the proposed Figure lighting. 2 outlines the proposed lighting.

Figure 2. OutlineOutline of of indoor ligh lightingting with UVB LEDs.

Two types of UVB LED light sources (LG InnoTek, Seoul, Korea) released in Korea were selected to provide safe UVB doses; their optical characteristics based on distances and applied currents were measured and analyzed. The two types of UVB LED light sources used in the experiment are shown in Table 3. The UVB LED light sources had an output power of 20 and 100 mW, respectively, and a current up to 350 mA could be applied.

Table 3. Specifications of UVB LEDs (LG InnoTek). Size(L*W*H) Peak Optical Maximum Model Name (mm) Wavelength Power(mW) Current[mA] LEUVA66G00KV00 6.0 × 6.0 × 1.35 295~315nm 20 350 LEUVA66H00KU00 6.0 × 6.0 × 1.35 300~310nm 100 350

For the experiment, two test lighting modules combining 10 light source modules (each 20 mW UVB led or 100 mW UVB led) were developed. The light characteristics of the two UVB LED light source modules were measured from distances of 30, 60, 50, 90, and 150 cm, and the results are shown in Figure 3. Appl. Sci. 2019, 9, 826 6 of 12

Two types of UVB LED light sources (LG InnoTek, Seoul, Korea) released in Korea were selected to provide safe UVB doses; their optical characteristics based on distances and applied currents were measured and analyzed. The two types of UVB LED light sources used in the experiment are shown in Table3. The UVB LED light sources had an output power of 20 and 100 mW, respectively, and a current up to 350 mA could be applied.

Table 3. Speciﬁcations of UVB LEDs (LG InnoTek).

Size (L*W*H) Peak Optical Power Maximum Current Model Name (mm) Wavelength (mW) [mA] LEUVA66G00KV00 6.0 × 6.0 × 1.35 295~315 nm 20 350 LEUVA66H00KU00 6.0 × 6.0 × 1.35 300~310 nm 100 350

(a) (b) (c)

FigureFigure 3.3. IrradianceIrradiance andand spectralspectral irradianceirradiance by distance step. ( (aa)) Measured Measured results results per per wavelength wavelength increments:increments: 100 100 mWmW UVBUVB LEDLED module;module; (b) measured measured results results per per wavelength wavelength increments: increments: 20 20 mW mW UVB UVB LEDLED module; module; ((cc)) irradianceirradiance calculationcalculation resultresult byby distancedistance step.

FigureFigures3a,b 3a,b show show the resultsthe results of the of 20 the mA 20 UVB mA LEDUVB and LED the and 100 mAthe 100 UVB mA LED UVB modules LED measured.modules Theirmeasured. irradiance Their decreased irradiance as decreased the distance as the from distance the lamp from increased. the lamp As increased. expected As for expected any light for source, any thelight irradiance source, the of theirradiance 20 mW of UVB the LED20 mW module UVB LED was 0.075module W/m was2 and0.075 0.004 W/m W/m2 and 20.004at 30 W/m and2 150 at 30 cm distances,and 150 cm respectively. distances, respectively. The irradiance The irradiance of the 100 of mWthe 100 UVB mW LED UVB module LED module was 0.326 was 0.326 W/m W/m2 and2 0.017and 0.017 W/m W/m2 at2 30 at cm30 cm and and 150 150 cm cm distances, distances, respectively. respectively. Further, Further, consideringconsidering the general general lighting lighting environment,environment, thethe distancedistance betweenbetween the measuremen measurementt equipment equipment and and the the lighting lighting was was set set to to 150 150 cm; cm; irradianceirradiance was was then then measuredmeasured accordingaccording toto the adju adjustmentstment of of the the applied applied current. current. Through Through increasing increasing thethe appliedapplied currentcurrent fromfrom 5050 toto 350350 mAmA byby 5050 mAmA over seven phases, their their UV UV characteristics characteristics were were measuredmeasured and and analyzed.analyzed. TheThe resultsresults areare shownshown in Table4 4..

Table 4. Irradiance of the UVB LED light source modules by applied current. (distance: 150 cm) (unit: W/m2). 20 mW UVB LED 100 mW UVB LED Applied Current (mA) UV UVB UVA EUVB EUVA UV UVB UVA EUVB EUVA 50 0.000640.000530.000110.000150.000000.002820.002180.000640.000400.00001 100 0.001310.001110.000200.000320.000000.005640.004390.001250.000800.00001 150 0.001960.001670.000290.000480.000000.008290.006460.001830.001180.00002 200 0.002620.002230.000390.000640.000000.010770.008370.002400.001520.00003 250 0.003240.002770.000470.000790.000010.013080.010120.002960.001820.00003 300 0.003860.003300.000560.000940.000010.015270.011730.003540.002100.00004 350 0.004490.003830.000660.001080.000010.017330.013220.004110.002340.00005

Although both modules used UVB LEDs, some of the optical characteristics of UVA were measured. However, the EUVA was close to 0 when the influence on the human body was weighted. Overall, it is expected that there will not be any harmful effects on the human body by UVA. In addition, the output of the applied current was proportional to the irradiance of UVB and EUVB, and it was confirmed that controlling the applied current can provide the required irradiance. The types and number of UVB light sources needed to support the synthesis of vitamin D were then selected. A previous study suggested that a EUV dose of 105 J/m2 is required to meet 200 IU of vitamin D when 6–10% of the body (of Korean individuals) is exposed [26]. Moreover, the synthesis of vitamin D increases in proportion to the exposed area of the body. Thus, in this paper, the target UVB dose was calculated as 70 J/m2, assuming that the area of the human body that was exposed in the room was 9–15%. When a current of 350 mA was applied to 20 mW and 100 mW UVB LED light sources for 16 Appl. Sci. 2019, 9, 826 7 of 12

Table 4. Irradiance of the UVB LED light source modules by applied current. (distance: 150 cm) (unit: W/m2).

Applied 20 mW UVB LED 100 mW UVB LED Current (mA) UV UVB UVA EUVB EUVA UV UVB UVA EUVB EUVA 50 0.00064 0.00053 0.00011 0.00015 0.00000 0.00282 0.00218 0.00064 0.00040 0.00001 100 0.00131 0.00111 0.00020 0.00032 0.00000 0.00564 0.00439 0.00125 0.00080 0.00001 150 0.00196 0.00167 0.00029 0.00048 0.00000 0.00829 0.00646 0.00183 0.00118 0.00002 200 0.00262 0.00223 0.00039 0.00064 0.00000 0.01077 0.00837 0.00240 0.00152 0.00003 250 0.00324 0.00277 0.00047 0.00079 0.00001 0.01308 0.01012 0.00296 0.00182 0.00003 300 0.00386 0.00330 0.00056 0.00094 0.00001 0.01527 0.01173 0.00354 0.00210 0.00004 350 0.00449 0.00383 0.00066 0.00108 0.00001 0.01733 0.01322 0.00411 0.00234 0.00005

Although both modules used UVB LEDs, some of the optical characteristics of UVA were measured. However, the EUVA was close to 0 when the inﬂuence on the human body was weighted. Overall, it is expected that there will not be any harmful effects on the human body by UVA. In addition, the output of the applied current was proportional to the irradiance of UVB and EUVB, and it was conﬁrmed that controlling the applied current can provide the required irradiance. The types and number of UVB light sources needed to support the synthesis of vitamin D were then selected. A previous study suggested that a EUV dose of 105 J/m2 is required to meet 200 IU of vitamin D when 6–10% of the body (of Korean individuals) is exposed [26]. Moreover, the synthesis of vitamin D increases in proportion to the exposed area of the body. Thus, in this paper, the target UVB dose was calculated as 70 J/m2, assuming that the area of the human body that was exposed in the room was

9–15%.Appl. Sci. When 2018, 8, a x current of 350 mA was applied to 20 mW and 100 mW UVB LED light sources for7 of 16 11 h, a EVUB dose of approximately 63 and 138 J/m2 was provided, respectively. Therefore, in order to provideh, a EVUB a EUVB dose doseof approximately of 70 J/m2 or 63 more, and 138 four J/m 202mW was UVBprovided, LEDs respectively. were selected Therefore, as UVB light in order sources. to Figureprovide4 shows a EUVB the dose general of 70 UVBJ/m2 or LED more, indoor four lighting20 mW UVB proposed LEDs inwere this selected study. Figureas UVB4 alight shows sources. both sidesFigure where 4 shows four the UVB general LEDs withUVB aLED 20 mWindoor output lighting speciﬁcation proposed are in attachedthis study. and Figure where 4a multi-channel shows both whitesides LEDswhere for four a brightnessUVB LEDs ofwith 500 a lux20 mW are placed.output specification are attached and where multi-channel white LEDs for a brightness of 500 lux are placed.

(a) (b) (c) (d)

Figure 4. General lighting of indoor UVB LEDs. (a) vis and UVB LED array; (b) diffusion plate; Figure 4. General lighting of indoor UVB LEDs. (a) vis and UVB LED array; (b) diffusion plate; (c) (c) control & power; (d) front (apply diffusion plate). control & power; (d) front (apply diffusion plate). Figure4b is a diffusion plate for a visible LED having a transmittance performance of Figure 4b is a diffusion plate for a visible LED having a transmittance performance of approximately 66%, and Figure4c is a controller and a power supply module for controlling brightness. approximately 66%, and Figure 4c is a controller and a power supply module for controlling An AC/DC converter with a 47 V output performance was applied to the power supply module, and brightness. An AC/DC converter with a 47 V output performance was applied to the power supply the controller was implemented to have up to DC 27 V of output through the LED channel. In addition, module, and the controller was implemented to have up to DC 27 V of output through the LED Figure4d shows the front proﬁle of the system after implementing a diffuser plate. Since UVB cannot channel. In addition, Figure 4d shows the front profile of the system after implementing a diffuser penetrate the diffuser plate, it was made to cover only visible LEDs. plate. Since UVB cannot penetrate the diffuser plate, it was made to cover only visible LEDs.

4. Results and Discussion The environment for measuring the optical characteristics of lighting was set as shown in Figure 5. First, a lighting box with a volume of 120 × 120 × 200 cm was used to cut off extraneous light, and a light was set in the upper part of it.

Figure 5. Environment for measuring optical characteristics.

In the lower part, a spectral radiometer was installed, and the distance between the light and the spectral radiometer was kept at 150 cm. The brightness of the light was adjusted to 500 lux. The spectral radiometer used was a CAS 140CT device capable of measuring wavelengths in the range of 200–800 nm. Figure 5 shows an environment for measuring the optical characteristics of the proposed lighting. Appl. Sci. 2018, 8, x 7 of 11 h, a EVUB dose of approximately 63 and 138 J/m2 was provided, respectively. Therefore, in order to provide a EUVB dose of 70 J/m2 or more, four 20 mW UVB LEDs were selected as UVB light sources. Figure 4 shows the general UVB LED indoor lighting proposed in this study. Figure 4a shows both sides where four UVB LEDs with a 20 mW output specification are attached and where multi-channel white LEDs for a brightness of 500 lux are placed.

(a) (b) (c) (d)

Figure 4. General lighting of indoor UVB LEDs. (a) vis and UVB LED array; (b) diffusion plate; (c) control & power; (d) front (apply diffusion plate).

Figure 4b is a diffusion plate for a visible LED having a transmittance performance of approximately 66%, and Figure 4c is a controller and a power supply module for controlling brightness. An AC/DC converter with a 47 V output performance was applied to the power supply module, and the controller was implemented to have up to DC 27 V of output through the LED channel. In addition, Figure 4d shows the front profile of the system after implementing a diffuser Appl. Sci. 2019, 9, 826 8 of 12 plate. Since UVB cannot penetrate the diffuser plate, it was made to cover only visible LEDs.

4. Results Results and and Discussion The environment forfor measuringmeasuring thethe opticaloptical characteristicscharacteristics of of lighting lighting was was set set as as shown shown in in Figure Figure5. 5.First, First, a lightinga lighting box box with with a volumea volume of of 120 120× 120× 12×0 ×200 200 cm cm was was used used to to cut cut off off extraneous extraneous light, light, and and a alight light was was set set in in the the upper upper part part of of it. it.

Figure 5. EnvironmentEnvironment for measuring optical characteristics.

In the lower lower part, a a spectral spectral radiometer radiometer was inst installed,alled, and the distance between the light and the spectral radiometerradiometer was was kept kept at at 150 150 cm. cm. The The brightness brightness of the of light the waslight adjusted was adjusted to 500 lux.to 500 The lux. spectral The spectralradiometer radiometer used was used a CAS was 140CT a CAS device 140CT capable device ofcapable measuring of measuring wavelengths wavelengths in the range in the of range 200–800 of 200–800nm.Appl. FigureSci. 2018 nm.5, 8showsFigure, x an5 shows environment an environment for measuring for measuring the optical the characteristics optical characteristics of the proposed of the proposed lighting.8 of 11 lighting.In this experiment, to conﬁrm the optical characteristics of the proposed lighting, one kind of commercialIn this experiment, LED lights was to confirm measured the and optical compared charac together,teristics of and the the proposed results are lighting, shown one in Figure kind 6of. commercial LED lights was measured and compared together, and the results are shown in Figure 6.

(a) (b) Figure 6. Spectral distribution of commercial and proposed general lighting. (a) General (normal) Figure 6. Spectral distribution of commercial and proposed general lighting. (a) General (normal) lighting; (b) proposed lighting (UV and visible). lighting; (b) proposed lighting (UV and visible). Figure6a shows the result of the measurement of LED lighting (merlot lighting, 655 × 318 × 83 mm) Figure 6a shows the result of the measurement of LED lighting (merlot lighting, 655 × 318 × 83 on the market that can be mounted on ceilings, showing the spectral irradiance of general lighting. mm) on the market that can be mounted on ceilings, showing the spectral irradiance of general Figure6b is the proposed general UVB LED indoor lighting. It shows the measurement result when lighting. Figure 6b is the proposed general UVB LED indoor lighting. It shows the measurement 200 mA is applied after applying four UVB LED light sources with the 20-mW output standard. Unlike result when 200 mA is applied after applying four UVB LED light sources with the 20-mW output the general lighting in Figure6a, the proposed lighting in Figure6b had a spectral distribution in the standard. Unlike the general lighting in Figure 6a, the proposed lighting in Figure 6b had a spectral distribution in the UV (280–400 nm) band. As a result of the experiment, the total irradiance of the proposed lighting of the UV and visible light had an irradiance of 1.75 W/m2. The EUV on which the erythema-weighted function of Equation (6) was applied in the spectral distribution in Figure 7b was calculated to check if erythema occurred on the skin. The calculated EUV was 0.00325794 W/m2, which is equivalent to 1/200 of that of natural light as shown in Figure 2. When exposed to the proposed lighting system for 16 h, the EUV dose was about 187.66 J/m2, which would not cause erythema for general skin types (Skip Types 1–6) [14]. In addition, a chemical hazard weighting function was applied for the UV zone to check the hazard on the human body by UVB-LED, with the results illustrated in Figure 7. Figure 7a shows the actinic hazard weighting function as well as the weighted value approaching the maximum of 1 at 300 nm or less. Figure 7b shows the spectral distributions before and after the application of the actinic hazard weighting function to the UV area of the proposed lighting. When the actinic hazard weighting function was applied, the hazard distribution was adjusted to the range of 280–320 nm from the existing UV wavelength range. The results of applying this to the AUV and NUV formulas (Equations (6) and (7)) are shown in Table 5. The measured values of AUV and NUV of the proposed lighting were 0.001 W/m2 and 0.002 W/m2, respectively, which are lower than the reference values of 0.001 W/m2 and 10 W/m2. Their hazard ratings are all considered Exempt, which is the safest rating. Appl. Sci. 2019, 9, 826 9 of 12

UV (280–400 nm) band. As a result of the experiment, the total irradiance of the proposed lighting of the UV and visible light had an irradiance of 1.75 W/m2. The EUV on which the erythema-weighted function of Equation (6) was applied in the spectral distribution in Figure7b was calculated to check if erythema occurred on the skin. The calculated EUV was 0.00325794 W/m2, which is equivalent to 1/200 of that of natural light as shown in Figure2. When exposed to the proposed lighting system for 16 h, the EUV dose was about 187.66 J/m2, which would not cause erythema for general skin types (Skip Types 1–6) [14]. In addition, a chemical hazard weighting function was applied for the UV zone Appl.to check Sci. 2018 the, 8, hazard x on the human body by UVB-LED, with the results illustrated in Figure7. 9 of 11

(a) (b)

FigureFigure 7. 7. SpectralSpectral distribution distribution of of the the proposed proposed lighting lighting (UV) and actinic hazard weightingweighting function.function. ((a)a) Weighting Weighting function function of of an an actinic actinic hazard; hazard (b;) Before(b) Before and and after after applying applying the the proposed proposed lighting lighting and the the actinic hazard weighting function. actinic hazard weighting function. Figure7a shows the actinic hazard weighting function as well as the weighted value approaching Table 5. Comparison of the IEC 62471 standard and UV general lighting measurement results. the maximum of 1 at 300 nm or less. Figure7b shows the spectral distributions before and after the applicationItem of the actinic hazardReference weighting Value functionResult toValue the UVafter area Measurement of the proposed Hazard lighting. Rating When Actinic ultraviolet hazard the actinic hazard weighting function0.001 W/m was2 applied, the hazard0.001 distribution W/m2 was adjustedExempt to the range of 280–320(AUV) nm from the existing UV wavelength range. The results of applying this to the AUV and Near-UV hazard (NUV) 10 W/m2 0.002 W/m2 Exempt NUV formulas (Equations (6) and (7)) are shown in Table5. The measured values of AUV and NUV

of the proposed lighting were 0.001 W/m2 and 0.002 W/m2, respectively, which are lower than the referenceWe also values applied of 0.001 the vitamin W/m2 and D synthesis 10 W/m2 amount. Their hazard (Equation ratings (8)) are derived all considered from the Exempt, previous which study tois confirm the safest whether rating. the synthesis of vitamin D is supported by the EUVB dose of the proposed lighting [33]. Table 5. Comparison of the IEC 62471W standard and UV general lighting measurement results. EUV Etimes s Earea % 40IU m (8) 𝑽𝒊𝒕𝒂𝒎𝒊𝒏 𝑫 Result Value after Item Reference ValueMED J/m Hazard Rating Measurement AtActinic this time, ultraviolet the expected hazard (AUV) amount of0.001 vitamin W/m D2 synthesis0.001 was W/m calculated2 by applyingExempt 0.003245 W/m2 of EUVBNear-UV irradiance, hazard (NUV) 16 h (57,600 s) of10 exposure W/m2 time (Etimes),0.002 W/m Skin2 Type 3 (Korean),Exempt and 15% of the exposed area (face, neck, hands, and arms) for the proposed lighting. As a result, it was confirmedWe also that applied 374 IU the of vitamin vitamin D synthesiscan be generated amount (Equationby providing (8)) derivedan EUVB from dose the of previous approximately study 187to J/m confirm2 through whether the proposed the synthesis lighting. of vitamin The Korean D is supported Nutrition bySociety the EUVB recommends dose of a the daily proposed vitamin Dlighting intake of [33 200]. IU per day for individuals aged from 20 to 49 and 400 IU for the remaining age groups [34]. Therefore, it was confirmed EUVthat itW/m is possible2 × Etimes to support[s] × theEarea synthesis[%] × of40IU vitamin D in the body Vitamin D = (8) through the proposed general indoor lighting. MED [J/m2] At this time, the expected amount of vitamin D synthesis was calculated by applying 0.003245 5. Conclusions and Future Research W/m2 of EUVB irradiance, 16 h (57,600 s) of exposure time (Etimes), Skin Type 3 (Korean), and 15% of theThis exposed study area proposes (face, neck, general hands, indoor and arms) UVB forLED the lighting proposed that lighting. produces As avitamin result, itD was for confirmedthe human bodythat by 374 reproducing IU of vitamin solar D can UV be characteristics. generated by providing UV ray intensity an EUVB was dose measured of approximately in summers 187 (noon), J/m2 and the characteristics of solar UVB were confirmed. To provide a safe level of UVB light, we measured and analyzed, based on distances and applied currents, the irradiance of two kinds of UVB LED light sources of 20 and 100 mW output specifications that could control the output of the applied current. To provide the UVB dose via indoor lighting, the application plan of each UVB LED light source was derived. We proposed general indoor UVB LED lighting with four 20 mW UVB LED light sources. The proposed lighting was controlled to have a brightness of 500 lux at a distance of 150 cm. EUVB irradiance of 0.00266 W/m2 was provided by applying a current of 200 mA to the UVB LED light source. The proposed lighting was then measured using a spectral radiometer (CAS 140CT) in a lighting box in which extraneous light was cut off. Additionally, a chemical hazard UV light item AUV and near‐UV light NUV, which are the UV rays’ hazard items of IEC 62471, were calculated. AUV and NUV were shown to be 0.001 and 0.002 W/m2, respectively; thus, both were found to be in the safest grade, Exempt. Moreover, the EUV calculation value to find out the incidence of erythema Appl. Sci. 2019, 9, 826 10 of 12 through the proposed lighting. The Korean Nutrition Society recommends a daily vitamin D intake of 200 IU per day for individuals aged from 20 to 49 and 400 IU for the remaining age groups [34]. Therefore, it was confirmed that it is possible to support the synthesis of vitamin D in the body through the proposed general indoor lighting.

5. Conclusions and Future Research This study proposes general indoor UVB LED lighting that produces vitamin D for the human body by reproducing solar UV characteristics. UV ray intensity was measured in summers (noon), and the characteristics of solar UVB were confirmed. To provide a safe level of UVB light, we measured and analyzed, based on distances and applied currents, the irradiance of two kinds of UVB LED light sources of 20 and 100 mW output specifications that could control the output of the applied current. To provide the UVB dose via indoor lighting, the application plan of each UVB LED light source was derived. We proposed general indoor UVB LED lighting with four 20 mW UVB LED light sources. The proposed lighting was controlled to have a brightness of 500 lux at a distance of 150 cm. EUVB irradiance of 0.00266 W/m2 was provided by applying a current of 200 mA to the UVB LED light source. The proposed lighting was then measured using a spectral radiometer (CAS 140CT) in a lighting box in which extraneous light was cut off. Additionally, a chemical hazard UV light item AUV and near-UV light NUV, which are the UV rays’ hazard items of IEC 62471, were calculated. AUV and NUV were shown to be 0.001 and 0.002 W/m2, respectively; thus, both were found to be in the safest grade, Exempt. Moreover, the EUV calculation value to find out the incidence of erythema by UV was 0.003245 W/m2. If a person were exposed to the proposed lighting for 16 h, the EUV dose would be about 187.66 J/m2, which would not cause erythema for general skin types (Skip Types 1–6). Furthermore, if the vitamin D calculation formula were applied as in the previous studies, a EUVB dose of about 187 J/m2 would be provided to produce 374 IU of vitamin D, provided that an Asian (Skin Type 3) exposing 15% of their body were exposed to the proposed lighting for 16 h. This suggests that general indoor UVB LED lighting that can synthesize vitamin D in humans by providing safe UVB light using a UVB LED light source that can control the applied current should be developed. In the future, research will be required to build a lighting control system that works with UV smart devices to provide users with an optimal UVB dose via UVB LED general lighting and to offer UVB lighting services for individual users. In addition, it is necessary to validate the safety of the proposed system by conducting a clinical test for more varied skin types and by cooperating with the experts of photobiology and dermatology, and to commercialize the proposed technology to resolve health issues such as vitamin D deficiency.

Author Contributions: Investigation, methodology, and writing of the original draft: S.-T.O. Conceptualization and supervision: J.-H.L. Investigation: D.-H.P. Acknowledgments: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2017R1A2B2005601). The research was supported by the International Science and Business Belt Program through the Ministry of Science and ICT (2015-DD-RD-0068-04). Conﬂicts of Interest: The authors declare no conﬂict of interest.

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