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