The Effect of Different Filament Arrangements on Thermal

applied sciences

Article The Eﬀect of Diﬀerent Filament Arrangements on Thermal and Optical Performances of LED Bulbs

Wei Wang 1, Jun Zou 1,*, Qiaoyu Zheng 1, Yuefeng Li 1 , Bobo Yang 1, Mingming Shi 1, Yang Li 2, Xinyu Li 3, Canyun Zhang 1, Cao Li 4 and Difei Chen 5 1 School of Science, Shanghai Institute of Technology, Shanghai 201418, China; [email protected] (W.W.); [email protected] (Q.Z.); [email protected] (Y.L.); [email protected] (B.Y.); [email protected] (M.S.); [email protected] (C.Z.) 2 School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, China; [email protected] 3 School of Science and Engineering, Curtin University of Technology, Kent Street, Bently 6102, Australia; [email protected] 4 Hangzhou Silan Azure Technology Co., Ltd., Hangzhou 310018, China; [email protected] 5 Zhejiang MKOPTO Co., Ltd., Shaoxing 312073, China; [email protected] * Correspondence: [email protected]; Tel.: +86-18957392108

Received: 24 December 2019; Accepted: 21 January 2020; Published: 18 February 2020

Abstract: The influences on thermal and optical performances of light emitting diode (LED) bulbs with three different filament arrangements are investigated in detail. The average junction temperature, temperature of the surface of the bulb, and luminous flux of three samples all increased with increasing power. The thermal performance test results show that between the average junction, temperature and power were linear. The junction temperatures of the three samples at a power of 3.5 W were 102.48, 98.46, and 88.88 ◦C. The optical performance test results revealed that the luminous flux and efficiency in the two vertical filament arrangements were closely related to each other and higher than that of the horizontal filament arrangement. A numerical model of LED filament bulbs was established by the Floefd 17.2 software for analyzing the temperature distribution of the cross section and the gas flow path inside the bulb. The simulation results illustrated that the average temperatures of three samples were 105.88, 101.83, and 96.12 ◦C. Additionally, the gas flow inside the bulb of the two vertical filament arrangements was subject to forming a thermal cycle during operation work more than that of the horizontal filament arrangement. As a result, the flexible spiral LED filament bulb is feasible as a new light source.

Keywords: thermal; optical; ﬁlament arrangement; led ﬁlament bulb

1. Introduction As a new light source, light emitting diodes (LEDs) are regarded as the fourth generation of solid-state lighting sources owing to their advantages of environmental friendliness, energy saving, long lifetime, quick start up, and so on [1–4]. So far, environment protection and energy saving have generated considerable research interest, the white light emitting diodes (WLEDs) have been developed rapidly in the commercial market and widely used in various lighting fields [5–7]. Early devices only provided lighting in one direction and could not meet the requirements for omnidirectional luminescent applications [8–10]. The flexible spiral LED filament bulbs combine the bulb shell of traditional incandescent bulbs with a new LED filament to achieve 360-degree illumination [11,12]. However, there is no effective radiator installed in the limited space, which seriously affects the thermal and optical performance of the filament. The heat generated by the chip is difficult to dissipate from inside of the bulb to the environment [13–16].

Appl. Sci. 2020, 10, 1373; doi:10.3390/app10041373 www.mdpi.com/journal/applsci Appl. Sci. 2020, 1, x 2 of 10

Appl. Sci. 2020, 10, 1373 2 of 10 The study of the effect of filament overheating, is of great value to the thermal design and management of LED filament bulbs. The properties of phosphors, such as the diameters, shapes, thickness,The study and concentration, of the effect may of filament affect the overheating, luminous flux is and of greatjunction value temperature to the thermal [11,17]. Liu design [17] andet al. management reduced the average of LED junction filament temperature bulbs. The of propertiesthe LED filament of phosphors, by optimizing such the as thesize diameters,of the bulb shapes,and the thickness, structure andof the concentration, phosphor. Moreover, may affect heat the luminousgenerated fluxfrom and LED junction chips temperatureis transferred [11 to, 17the]. Liusurface [17] etof al.the reduced filament the by average conduction, junction then temperature transferred of to the the LED bulb filament shell by by convection, optimizing and the sizefinally of thedissipated bulb and to the the structure environment of the [18,19 phosphor.]. LED Moreover, filament bulbs heat generatedmainly rely from on convection LED chips isheat transferred dissipation to theand surface have a of poor the filamentheat dissipation by conduction, performance then transferred [17,20,21]. to The the previous bulb shell report by convection, put forward and several finally dissipatedplans. to the environment [18,19]. LED filament bulbs mainly rely on convection heat dissipation and haveHigh a poorthermal heat conductive dissipation materials performance and [17 high,20, 21th].ermal The previousconductive report gases put are forward chosen several to decrease plans. the averageHigh thermal junction conductive temperature materials of the andLED high filament thermal [15,22,23]. conductive To increase gases are the chosen flow of to gas decrease inside thethe averagebulb, Xu junction [24] et al. temperature used ionic wind of the to LED improve filament the [heat15,22 dissipation,23]. To increase ability the of LED flow filament of gas inside bulb. theIt was bulb, also Xu necessary [24] et al. usedto consider ionic wind the optical to improve and thermal the heat properties dissipation with ability various of LED currents filament [24–26]. bulb. ItNevertheless, was also necessary they did to not consider study thethe opticaleffect of and different thermal filament properties arrangements with various on currentsthe thermal [24– 26and]. Nevertheless,optical performances, they did nor not did study they the design effect and of di simulatefferent filament the temperature arrangements distribution on the and thermal gas flow and opticalpath inside performances, the bulbs, norso it did was they worthwhile design and to an simulatealyze the the thermal temperature and optical distribution performances and gas during flow paththe operating inside the time. bulbs, so it was worthwhile to analyze the thermal and optical performances during the operatingHence, the time. purpose of this paper is to investigate the thermal and optical performances of flexibleHence, spiral the purposeLED filaments of this paper bulbs is towith investigate three different the thermal filament and optical arrangements. performances The of junction flexible spiraltemperature, LED filaments temperature bulbs of with surface three bulb, different luminous filament flux, arrangements. and luminous Theefficiency junction of LED temperature, filament temperaturebulbs are studied. of surface In bulb, addition, luminous for flux,better and analysis luminous and effi understandingciency of LED filamentof the bulbsprinciple are studied.of heat Indissipation addition, forof LED better filament analysis bulbs, and understandingsimulation models of the were principle carried of out. heat dissipation of LED filament bulbs, simulation models were carried out. 2. Experimental Method 2. Experimental Method 2.1. Flexible Spiral Light Emitting Diode (LED) Filament Bulb Structure 2.1. Flexible Spiral Light Emitting Diode (LED) Filament Bulb Structure The main work of this paper is to examine the thermal and optical performances of LED bulbs withThe different main work filament of this arrangements. paper is to examine In addition the thermal to the and driving optical equipment performances and ofthe LED lamp bulbs cap, with the ditypicalfferent flexible filament spiral arrangements. LED filament In addition bulb is tomain thely driving composed equipment of two and parts: the lampa flexible cap, thespiral typical LED flexiblefilament spiral with LEDmade filament by aluminum bulb isor mainly aluminum composed alloy and of twoa glass parts: bulb a shell flexible with spiral filling LED air. There filament are with99 chips made evenly by aluminum distributed or aluminum on the flexible alloy spiral and a glassfilament bulb substrate shell with with filling a length air. There of 26 are cm. 99 A chips few evenlycommercially distributed available on the LED flexible filament spiral filamentbulbs, which substrate rate withtheir a voltage length of at 26 260 cm. V, A were few commerciallybought from availableZhejiang LEDEmitting filament Optoelectronic bulbs, which Technology rate their voltageCo., Ltd at., and 260 V,tested were to bought obtain fromvalid Zhejiang and reliable Emitting data. OptoelectronicAs mentioned Technology above, Co.,the flexible Ltd., and spiral tested LED to obtainbulbs have valid three and reliabledifferent data. filament arrangements, namelyAs mentioneda horizontal above, filament the flexiblearrangement spiral LEDand two bulbs vertical have threefilame dintfferent arrangements filament arrangements,with different namelystretch height, a horizontal as shown filament below arrangement in Figure 1. and two vertical filament arrangements with different stretch height, as shown below in Figure1.

FigureFigure 1.1. Three different different filament filament arrangements arrangements of of flexib flexiblele spiral spiral light light emitting emitting diode diode (LED) (LED) bulbs. bulbs. (1) (1Horizontal) Horizontal filament filament arrangement arrangement with with a stretch a stretch height height of 3 ofcm. 3 cm.(2) Vertical (2) Vertical filament filament arrangement arrangement with witha stretch a stretch height height of 3 ofcm. 3 ( cm.3) Vertical (3) Vertical filament filament arrangement arrangement with with a stretch a stretch height height of 5 ofcm. 5 cm. Appl. Sci. 2020, 10, 1373 3 of 10

2.2. ExperimentalAppl. Sci. Measurement 2020, 1, x 3 of 10 To obtain2.2. the Experimental thermal and Measurement optical data, two experiments were done. In one experiment, the average junction temperature,To obtain temperature the thermal of and the surfaceoptical data, bulb two and ex thermalperiments resistance were done. of threeIn one di experiment,fferent filament the arrangementsaverage were measuredjunction temperature, by instrument temperature (LED-T300B, of the surface as shown bulb inand Figure thermal2a) resistance with an accuracyof three of 0.15 C fromdifferent LEETS filament Lighting arrangements Shanghai were Co., measured Ltd., which by instrument is based (LED-T300B, on the forward as shown voltage in Figure mothed. 2a) ± ◦ Figure2b showswith the an thermocouplesaccuracy of ±0.15 attached °C from LEETS to the Lighting surface Shanghai of the vertically Co., Ltd., placed which is bulb. based The on the relationship forward between thevoltage temperature mothed. and Figure power 2b shows of these the thermocouples LED devices wasattached recorded to the surface at steady of the state vertically and is placed shown bulb. The relationship between the temperature and power of these LED devices was recorded at in Figure3. Thesteady temperature state and is wasshown measured in Figure by3. The at leasttemper twoature thermocouples was measured by during at least the two operation, thermocouples so the data is the meanduring value. the operation, In another so experiment,the data is the themean optical value. performance In another experiment, of these the LED optical devices, performance including luminous fluxof andthese luminous LED devices, effi cacy,including was testedluminous through flux and an luminous integrating efficacy, sphere was from tested the through EVERFINE an corporation,integrating with the results sphere from as shown the EVERFINE in Figure corporat4. ion, with the results as shown in Figure 4.

Appl. Sci. 2020, 1, x 5 of 10 Figure 2. (a) JunctionFigure 2. temperature (a) Junction testing temperature instrument testing (LED-T300B). instrument (LED-T300B). (b) LED filament (b) LED bulb filament with thermocouple. bulb with thermocouple.

2.3. Simulation Model A 3-D computational model was established to enable a more intuitive observation and analysis of the temperature distribution and the gas flow of inside the bulb. Figure 5 shows the multi-block unstructured meshes which was generated by FLOEFD 17.2 software in all the domains. The computational model is composed of 3842886 grids for thermal behavior simulation. Some hypotheses completing the numerical model were made as shown below: (1) Wires are neglected in the simulation model. (2) The thermophysical properties of each material are independent of temperature. (3) All the material interfaces in the spiral flexible LED filament are perfectly connected. (4) The thermal radiation of the LED filament can be ignored owing to its small contact area. (5) The GaN chip is a volume heat source with a power of 2.45 W. (6) The laminar flow was three dimensional and steady. (7) The ideal gas flow was used to compute the densities of gases, whose other physical characteristics of gas depend on temperature and pressure. (8) The ambient temperature is set at 20 °C. The major thermal physical parameters of LED filament bulbs were shown in Table 1. At present, the efficiency of LED converting input power into heat is 70%–80% [17,27,28], so the total heat dissipation rate is 2.45 W when the power is 3.5 W for the thermal design. The simulation results of temperature distribution and gas flow path of three different filament arrangements are shown in Figure 6.

Figure 3. FigureTemperature 3. Temperature performances performances of three of dithreefferent different filament filament arrangements: arrangements: (a )( Junctiona) Junction temperature under ditemperaturefferent powers. under different (b) Steady powers. state (b) Steady process state process of junction of junction temperature temperature at a apower power of of 3.5 W. (c) Temperature3.5 W. (c) of Temperature surface bulb. of surface (d) Thermalbulb. (d) Thermal resistance. resistance.

3.2. Illuminance Performance of LED Filament Bulbs Figure 4 shows the optical performance of three different filament arrangements with increasing power. The luminous flux and luminous efficacy of LED filament bulbs were all considered. The luminous flux of LED filament bulbs increases with the increase of power. However, the luminous efficacy is opposite to the luminous flux, and decreases with the increase of power. The luminous flux and efficacy of sample 1 at all input powers is lower than that of the others owing to its high junction temperature and poor heat dissipation. Without appropriate heat dissipation, the junction temperature of the chip increases with the increase of power, which seriously reduces the efficiency of the photoelectric conversion of the chip. In addition, the luminous flux and efficacy curves of sample 2 and 3 are very closely related to each other and higher than that of sample 1, indicating that the vertical filament arrangement seems to be effective for the illuminance performance of flexible spiral LED filament bulbs. Appl. Sci. 2020, 10, 1373 4 of 10 Appl. Sci. 2020, 1, x 6 of 10

Appl. Sci. 2020, 1, x 6 of 10

Figure 4.4. Luminous fluxflux (a) and luminous eefficiencyfficiency (b) of the three didifferentfferent filamentfilament arrangementsarrangements under didifferentfferent powers.powers.

2.3.3.3. Simulation ModelResults of LED Filament Bulbs AFigure 3-D 5 computational shows the multi-block model was unstructured established meshing to enable which a morewas generated intuitive observationby FLOEFD and17.2 analysissoftware ofin theall the temperature domains. The distribution simulation and result thes gas of flowthe three of inside different the filament bulb. Figure arrangements5 shows the are multi-blockshown in Figure unstructured 6. The simulation meshes which average was generatedjunction temperatures by FLOEFD17.2 of the software three indifferent all the domains.filament Thearrangements computational are 105.88, model 101.83, is composed and 96.12 of 3842886°C, and gridsthe error for thermal with the behavior actual results simulation. of the Somethree hypothesesdifferent filaments completing arrangement the numerical are 3.21%, model 3.31%, were made and 7.53% as shown respectively. below: Therefore, these models aere available. (1) WiresFigure are4. Luminous neglected flux in the(a) and simulation luminous model. efficiency (b) of the three different filament arrangements (2) Theunder thermophysical different powers. properties of each material are independent of temperature. (3) All the material interfaces in the spiral flexible LED filament are perfectly connected. (4)3.3. SimulationThe thermal Results radiation of LED of Filament the LED Bulbs filament can be ignored owing to its small contact area. (5) TheFigure GaN 5 shows chip is the a volume multi-block heat source unstructured with a power meshing of 2.45 which W. was generated by FLOEFD 17.2 (6)softwareThe laminarin all the flow domains. was three The dimensionalsimulation result and steady.s of the three different filament arrangements are (7)shown The in ideal Figure gas flow6. The was simulation used to compute average the junction densities temperatures of gases, whose of otherthe three physical different characteristics filament arrangementsof gas depend are 105.88, on temperature 101.83, and and 96.12 pressure. °C, and the error with the actual results of the three

(8)differentThe ambientfilaments temperature arrangement is setare at3.21%, 20 ◦C. 3.31%, and 7.53% respectively. Therefore, these models aere available.

Figure 5. Mesh of the numerical simulation model.

FigureFigure 5.5.Mesh Mesh ofof thethe numericalnumerical simulationsimulation model.model.

The major thermal physical parameters of LED ﬁlament bulbs were shown in Table1. At present, the eﬃciency of LED converting input power into heat is 70%–80% [17,27,28], so the total heat dissipation rate is 2.45 W when the power is 3.5 W for the thermal design. The simulation results of

Figure 6. Temperature distribution of three different filament arrangements.

Figure 6. Temperature distribution of three different filament arrangements. Appl. Sci. 2020, 1, x 6 of 10

Figure 4. Luminous flux (a) and luminous efficiency (b) of the three different filament arrangements under different powers.

Appl. Sci. 2020, 10, 1373 5 of 10 temperature distribution and gas flow path of three different filament arrangements are shown in Figure6.

Table 1. Thermal physical parameters of LED ﬁlament bulbs.

Item Thermal Conductivity Reference LED chip 150 [7,12,13] Substrate (Al) 237 [13 ,16] Phosphor 0.3 [7,11] FigureGlass bell5. Mesh of the numerical 0.9 simulation model. [15,16]

Figure 6. Temperature distribution of three different filament arrangements. Figure 6. Temperature distribution of three different filament arrangements. 3. Results and Discussions In order to illustrate that the thermal and optical performances of three different filament arrangements of flexible spiral LED bulbs, the average junction temperature, temperature of the surface bulb, and thermal resistance were measured for analyzing the effects on heat dissipation. The luminous flux and luminous efficacy were also measured to analyze the optical characteristics. Furthermore, the design and simulation of three different filament arrangements was carried out to analyze the temperature distribution and the gas flow inside the bulb. Due to the different filament arrangements, the LED filament bulbs exhibit different thermal and optical properties.

3.1. Temperature Performance of LED Filament Bulbs Figure3 shows the temperature performance of three di fferent filament arrangements at different power levels. Both experiments were carried out at room temperature of 20 ◦C. As shown in Figure3a, the average junction temperature of three different arrangements has a wide gap, which all increased with increasing power and are linear. The temperature–power coefficients of the sample 1, 2 and 3 are 22.87, 22.24, and 22.10 K/w, respectively. Table2 lists the linear fitting expressions of the three different filament arrangements. The linearity is the absolute difference between the actual value and the theoretical value divided by the actual value, and the formula is δ = (∆Y/Y) 100%. As given in × Figure3b, the average junction temperature at a power of 3.5 W for the three di fferent filaments is 102.48, 98.46, and 88.88 ◦C, respectively.

Table 2. Linear fitting results of three different filament arrangements.

Item Linear Fitting Linearity (δ) Sample 1 Y = 22.87X + 22.44 1.05% Sample 2 Y = 22.24 X + 21.34 1.07% Sample 3 Y = 20.09X + 19.50 1.16% Appl. Sci. 2020, 10, 1373 6 of 10

The average junction temperature of sample 1 was increased by 4.08% and 15.30% compared with sample 2 and 3. This is because when the filament bulb is placed vertically, it is more difficult for a horizontal filament arrangement to form convection within the bulb. Additionally, the heat source volume of samples 1 and 2 is larger than that of sample 3. Figure3c shows the temperature of the surface of the bulb of the three different filament arrangements rising slowly with increasing power. Figure3d shows the thermal resistance characteristics of the three di fferent filament arrangements at different power levels. Thermal resistance decreases slowly with the increase of power. This is because the thermal power consumption of LED filament bulbs increases with the increase of power. According to the expression of thermal resistance and power:

Tj Ta R = − (1) th P where Tj is the junction temperature of the LED ﬁlament, and Ta is the temperature of the surface bulb. As can be seen, the thermal resistance of sample 3 is the lowest compared to sample 1 and 2, which is attributed to good convection heat dissipation. Generally, it can be concluded that the lower junction temperature and thermal resistance is associated with the vertical ﬁlament arrangement with a stretch height of 5 cm.

3.2. Illuminance Performance of LED Filament Bulbs Figure4 shows the optical performance of three di fferent filament arrangements with increasing power. The luminous flux and luminous efficacy of LED filament bulbs were all considered. The luminous flux of LED filament bulbs increases with the increase of power. However, the luminous efficacy is opposite to the luminous flux, and decreases with the increase of power. The luminous flux and efficacy of sample 1 at all input powers is lower than that of the others owing to its high junction temperature and poor heat dissipation. Without appropriate heat dissipation, the junction temperature of the chip increases with the increase of power, which seriously reduces the efficiency of the photoelectric conversion of the chip. In addition, the luminous flux and efficacy curves of sample 2 and 3 are very closely related to each other and higher than that of sample 1, indicating that the vertical filament arrangement seems to be effective for the illuminance performance of flexible spiral LED filament bulbs.

3.3. Simulation Results of LED Filament Bulbs Figure5 shows the multi-block unstructured meshing which was generated by FLOEFD 17.2 software in all the domains. The simulation results of the three different filament arrangements are shown in Figure6. The simulation average junction temperatures of the three di fferent filament arrangements are 105.88, 101.83, and 96.12 ◦C, and the error with the actual results of the three different filaments arrangement are 3.21%, 3.31%, and 7.53% respectively. Therefore, these models aere available. The left-hand of Figure7 illustrates the temperature distribution of cross sections of LED filament bulbs. As can be seen, the heat of samples 2 and 3 is mainly concentrated on the top end of the filament due to the filament formed by the geometry of the chimney prompting heat convection, and that of sample 1 concentrated on the middle of the filament due to the lack of thermal cycling inside the bulb. The intermediate figures in Figure7 illustrate the gas flow path inside the bulb of three di fferent filament arrangements. The plume of heated gas rose from the bottom of the bulb shell, then turned downward along the inner surface of the bulb shell, and then arrived at the top part of bulb shell. Comparing sample 2 with sample 3, we find that the thermal cycling path inside the bulb is relatively longer and symmetrical resulting in a large aspect ratio of heat source volume, further promoting natural convection to improve heat dissipation performance [19]. Moreover, the heat of sample 1 rises from both ends of the filament to the top of the bulb and falls along the inner surface of the bulb shell, but it is difficult to pass through the filament to form a thermal cycle in limited space. Appl. Sci. 2020, 1, x 7 of 10

The left-hand of Figure 7 illustrates the temperature distribution of cross sections of LED filament bulbs. As can be seen, the heat of samples 2 and 3 is mainly concentrated on the top end of the filament due to the filament formed by the geometry of the chimney prompting heat convection, and that of sample 1 concentrated on the middle of the filament due to the lack of thermal cycling inside the bulb. The intermediate figures in Figure 7 illustrate the gas flow path inside the bulb of three different filament arrangements. The plume of heated gas rose from the bottom of the bulb shell, then turned downward along the inner surface of the bulb shell, and then arrived at the top part of bulb shell. Comparing sample 2 with sample 3, we find that the thermal cycling path inside the bulb is relatively longer and symmetrical resulting in a large aspect ratio of heat source volume, further promoting natural convection to improve heat dissipation performance [19]. Moreover, the heat of sample 1 rises from both ends of the filament to the top of the bulb and falls along the inner surfaceAppl. Sci. of2020 the, 10 bulb, 1373 shell, but it is difficult to pass through the filament to form a thermal cycle7 of in 10 limited space.

FigureFigure 7. 7. TheThe cross-section cross-section temperature temperature distribution distribution and and th thee gas gas flow flow path path of of three three different different filament filament arrangementsarrangements ( (aa)–(–cc)) of of LED LED bulbs. bulbs.

BasedBased on on the the above above experiment experiment and and simulation, simulation, the the orientation orientation of of the the bulb bulb has has an an important important influenceinfluence on on the the junction junction temperature temperature [24]. [24]. As As shown shown in in Figure Figure 8,8, when the direction of gravity was the same as the direction of the filament, the bulb has the lowest junction temperature and exhibits excellent convective heat dissipation performance. The LED filament bulb with a stretch height of 5 cm has the lowest temperature in all three directions. The results show that the heat source formed by the filament was smaller and easier to release heat. Appl. Sci. 2020, 1, x 8 of 10 the same as the direction of the filament, the bulb has the lowest junction temperature and exhibits excellent convective heat dissipation performance. The LED filament bulb with a stretch height of 5 cm has the lowest temperature in all three directions. The results show that the heat source formed byAppl. the Sci. filament2020, 10, 1373was smaller and easier to release heat. 8 of 10

Figure 8. The junction temperature of LED filaments in various measuring orientations. (a) Measuring Figure 8. The junction temperature of LED filaments in various measuring orientations. (a) Measuring orientations of LED filament bulb; (b) Simulation results of three different filament bulbs. orientations of LED filament bulb; (b) Simulation results of three different filament bulbs. 4. Conclusions 4. Conclusions This paper investigated the thermal and optical performances for examining heat transfer characteristicsThis paper of investigated LED bulbs with the threethermal different and filamentoptical performances arrangements, for which examining including heat a horizontal transfer characteristicsarrangement andof LED two bulbs vertical with arrangements three different with filament different arrangements, stretch heights. which including The average a horizontal junction arrangementtemperature, and temperature two vertical of surface arrangements bulb, thermal with resistance,different stretch luminous heights. flux, andThe eaveragefficiency junction of these temperature,devices were temperature measured and of compared.surface bulb, The thermal average resistance, junction temperatureluminous flux, of threeand efficiency different filamentof these devicesarrangements were measured all increases and with compared. rises of The power average and arejunction linear. temperature The junction of temperature three different of samplefilament 1 arrangementsand sample 2 atall aincreases power of with 3.5 W rises were of improvedpower and by are 47.24% linear. and The 10.78% junction compared temperature with of sample sample 3 at1 and90 sample. The luminous 2 at a power flux of of 3.5 the W three were di improvedfferent filament by 47.24% arrangements and 10.78% also compared increases with with sample increasing 3 at − ◦ −power,90°. The but luminous the thermal flux resistanceof the three and different luminous fila ementfficiency arrangements of three di alsofferent increases filament with arrangements increasing power,decreased but due the tothermal the increased resistance power and consumption. luminous effi Meanwhile,ciency of three the different optical characteristics filament arrangements of samples decreased2 and 3 are due close to the to each increased other power and higher consumption. than that Meanwhile, of sample 1, the indicating optical characteristics that the vertical of samples filament 2arrangement and 3 are close has to the each best other thermal and and higher optical than performances. that of sample 1, indicating that the vertical filament arrangementSimulation has modelsthe best oftherma the LEDl and bulbsoptical with performances. three different filament arrangements were built to analyzeSimulation the temperaturemodels of the distribution LED bulbs ofwith the three cross di sectionfferent andfilament air flowarrangements path of the were inner built bulb. to analyzeThe simulation the temperature of average distribution junction temperature of the cross of threesection di ffanderent air filament flow path arrangements of the inner were bulb. 120.99, The simulation of average junction temperature of three different filament arrangements were 120.99, 101.83, and 96.12 ◦C. Compared to sample 1, the gas inside the bulbs of samples 2 and 3 is subject to 101.83,forming and a thermal 96.12 °C. cycle. Compared From the to resultssample of 1, the the analysis, gas inside the the vertical bulbs filament of samples with 2 aand stretching 3 is subject height to formingof 5 cm showeda thermal excellent cycle. From thermal the andresults illuminance of the analys performanceis, the vertical characteristics. filament with The a stretching presented height results ofmay 5 cm serve showed as a guideexcellent in the thermal heat dissipation and illuminance design pe ofrformance high-power characteristics. LED filament The bulbs. presented results may serve as a guide in the heat dissipation design of high-power LED filament bulbs. Author Contributions: Resources, software and writing—original draft, W.W.; Funding acquisition, J.Z.; AuthorData Curation, Contributions: Q.Z., B.Y., Resources, M.S., Y.L. software (Yang and Li), writing-original X.L., C.Z., C.L. anddraft, D.C.; W.W.; Software Funding and acquisition, Data Curation, J.Z.; Data Y.L. Curation,(Yuefeng Li).Q.Z., All B.Y., authors M.S., haveY.L. read(Yang and Li), agreed X.L., C.Z.; to the Soft publishedware and version Data Curation, of the manuscript. Y.L. (Yuefeng Li). All authors have read and agreed to the published version of the manuscript. Funding: The work was supported by the Science and Technology Planning Project of Zhejiang Province, Funding:China (2018C01046), The work was Enterprise-funded supported by the Science Latitudinal and Technolo Researchgy Projects Planning (J2016-141), Project of Zhejiang (J2017-171), Province, (J2017-293), China (2018C01046),(J2017-243). Enterprise-funded Latitudinal Research Projects (J2016-141), (J2017-171), (J2017-293), (J2017-243). Conflicts of Interest: The authors declared that they have no conflict of interest to this work. We declare that we Conflictsdo not have of Interest: any commercial The authors or associative declared that interest they that have represents no conflic ats conflict of interest of interest to this inwork. connection We declare with that the wework do submitted.not have any The commercial funders had or provided associative equipment interest andthat datarepresents analysis a conflict in the study. of interest in connection with the work submitted. The funders had provided equipment and data analysis in the study. References

1. Luo, X.; Hu, R.; Liu, S.; Wang, K. Heat and ﬂuid ﬂow in high-power LED packaging and applications. Prog. Energy Combust. Sci. 2016, 56, 1–32. [CrossRef] Appl. Sci. 2020, 10, 1373 9 of 10

2. Krames, M.R.; Shchekin, O.B.; Mueller-Mach, R.; Mueller, G.O.; Zhou, L.; Harbers, G.; Craford, M.G. Status and future of high-power light-emitting diodes for solid-state lighting. J. Disp. Technol. 2007, 3, 160–175. [CrossRef] 3. Jang, D.; Park, S.; Lee, K.S. Thermal performance of a PCB channel heat sink for LED light bulbs. Int. J. Heat Mass Transf. 2015, 89, 1290–1296. [CrossRef] 4. Peng, Y.; Li, R.; Wang, S.; Chen, Z.; Nie, L.; Chen, M. Luminous Properties and Thermal Reliability of Screen-Printed Phosphor-in-Glass-Based White Light-Emitting Diodes. IEEE Trans. Electron. Dev. 2017, 64, 1114–1119. [CrossRef] 5. Weng, C.J. Advanced thermal enhancement and management of LED package. Int. Commun. Heat Mass Transf. 2009, 36, 245–248. [CrossRef] 6. Montoya, F.G.; Peña-García, A.; Juaidi, A.; Manzano-Agugliaro, F. Indoor lighting techniques: An overview of evolution and new trends for energy saving. Energy Build. 2017, 140, 50–60. [CrossRef] 7. Shyu, J.C.; Hsu, K.W.; Yang, K.S.; Wang, C.C. Orientation effect on heat transfer of a shrouded LED backlight panel with a plate-fin array. Int. J. Heat Mass Transf. 2013, 42, 51–54. [CrossRef] 8. Park, S.J.; Jang, D.; Yook, S.J.; Lee, K.S. Optimization of a chimney design for cooling efficiency of a radial heat sink in a LED downlight. Energy Convers. Manag. 2016, 114, 180–187. [CrossRef] 9. Chi, W.H.; Chou, T.L.; Han, C.N.; Yang, S.Y.; Chiang, K.N. Analysis of Thermal and Luminous Performance of MR-16 LED Lighting module. IEEE Trans. Compon. Packag. Technol. 2010, 33, 713–721. [CrossRef] 10. Huang, B.J.; Tang, C.W. Thermal-electrical-luminous model of multi-chip polychromatic LED luminaries. Appl. Therm. Eng. 2009, 19, 3366–3373. [CrossRef] 11. Li, S.; Chen, H.; Tan, S.C.; Hui, S.R.; Waffenschmidt, E. Power Flow Analysis and Critical Design Issues of Retrofit Light-Emitting Diode (LED) Light bulb. IEEE Trans. Power Electron. 2014, 30, 3830–3840. [CrossRef] 12. Liu, Z.Y.; Liu, S.; Wang, K.; Luo, X.B. Studies on Optical Consistency of White LEDs Affected by Phosphor Thickness and Concentration Using Optical Simulation. IEEE Trans. Compon. Packag. Technol. 2010, 33, 680–687. [CrossRef] 13. Liu, S.M.; Chen, C.F.; Chou, K.C. The design and implementation of a low-cost 360-degree color LED display system. IEEE Trans. Consum. Electron. 2011, 57, 289–296. [CrossRef] 14. Park, S.J.; Jang, D.; Lee, K.S. Thermal performance improvement of a radial heat sink with a hollow cylinder for LED downlight application. Int. J. Heat Mass Transf. 2015, 89, 1184–1189. [CrossRef] 15. Feng, W.; Feng, B.; Zhao, F.; Shieh, B.; Lee, R. Simulation and optimization on thermal performance of LED filament light bulb. In Proceedings of the 2015 12th China International Forum on Solid State Lighting, Shenzhen, China, 2–4 November 2015; pp. 88–92. 16. Wang, L.P.; Li, W.B.; Xu, Y.C.; Yang, B.B.; Shi, M.M.; Zou, J.; Li, Y.; Qian, X.L.; Zheng, F.; Yang, L. Effect of different bending shape on thermal properties of flexible LED filament. Chin. Phys. B 2018, 27, 430–436. 17. Liu, J.; Xu, C.; Zheng, H.; Liu, S. Numerical Analysis and Optimization of Thermal Performance of LED filament Light Bulb. In Proceedings of the 2017 IEEE 67th Electronic Components and Technology Conference (ECTC), Orlando, FL, USA, 30 May–2 June 2017; pp. 2243–2248. 18. Luo, X.B.; Mao, Z.M.; Liu, S. Thermal design of a 16W LED bulb based on thermal analysis of a 4W LED bulb. In Proceedings of the Electronic Components & Technology Conference, Las Vegas, NV, USA, 1–4 June 2010; pp. 1906–1911. 19. Petroski, J. Advanced natural convection cooling designs LED bulb systems. J. Electron. Packag. 2014, 136, 041005. [CrossRef] 20. Tran, N.T.; Shi, F.G. Studies of phosphor concentration and thickness for phosphor-based white light-emitting-diode. J. Lightwave Technol. 2008, 26, 3556–3559. [CrossRef] 21. Yang, X.F.; Liu, J.; Chen, Q.; Shen, Y.P.; Liu, H.Z.; Lai, G.Q. A low temperature Vulcanized transparent silane modified epoxy resins for LED filament bulb package. Chin. J. Polym. Sci. 2018, 36, 114–121. [CrossRef] 22. Yu, X.; Xie, B.; Shang, B.; Chen, Q.; Luo, X. A Cylindrical Tuber Encapsulant Geometry for Enhancing Optical Performance of Chip-on-Board Packaging Light-Emitting Diodes. IEEE Photonics J. 2016, 8, 1–9. [CrossRef] 23. Li, B.; Baik, Y.J.; Chan, B. Enhanced natural convection heat transfer of a chimney-based radial heat sink. Energy Convers. Manag. 2016, 108, 422–428. [CrossRef] 24. Xu, C.; Zhang, Z.; Chu, J.; Wu, J.; Lei, X.; Zheng, H.; Liu, S. Thermal dissipation enhancement of LED filament bulb by ionic wind. In Proceedings of the International Conference on Electronic Packaging Technology, Wuhan, China, 16–19 August 2016; pp. 1212–1215. Appl. Sci. 2020, 10, 1373 10 of 10

25. Rao, F.; Ge, Z.C.; Zhu, J.L. Effect of Temperature and Current on luminous Efficiency of High-Power LED. Adv. Mater. Res. 2012, 347, 310–315. [CrossRef] 26. Wang, L.P.; Zou, J.; Yang, B.B.; Li, W.B.; Li, Y.; Shi, M.M.; Zhu, W.; Zhang, C.Y.; Wang, F.C.; Lin, Y.J. Optical and electrical properties of a spiral LED filament. J. Semicond. 2018, 39, 024003. [CrossRef] 27. Vairavan, R.; Sauli, Z.; Retnasamy, V.; Ismail, R.C.; Nor NI, M.; Nadzri, N.S.; Kamarudin, H. High power LED thermal and stress simulation on copper slug. In Proceedings of the Uksim International Conference on Computer Modelling & Simulation, Cambridge, UK, 10–12 April 2013; pp. 294–298. 28. Jang, D.; Park, S.J.; Yook, S.J.; Lee, K.S. The orientation effect for cylindrical heat sinks with application to LED light bulb. Int. J. Heat Mass Transf. 2014, 71, 496–502. [CrossRef]

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