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Research ArticleOptimization of Helium Inflating on Heat Dissipation andLuminescence Properties of the A60 LED Filament Lamps
Yizhan Chen , Qingguang Zeng, Lite Zhao, Yuanxing Li, Guangyao Huang, and Bingqian Li
School of Applied Physics and Materials, Wuyi University, Jiangmen, Guangdong, China
Correspondence should be addressed to Yizhan Chen; [email protected]
Received 15 September 2018; Revised 12 January 2019; Accepted 14 February 2019; Published 2 April 2019
Academic Editor: Alberto Álvarez-Gallegos
Copyright © 2019 Yizhan Chen et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
LED filament lamp has the characteristics of nearly 360° lighting angle, high brightness, and low energy consumption, turning itgradually into the best substitute for traditional incandescent lamps. At present, due to the limitations of heat dissipation, thedevelopment of high-power LED filament lamp is restricted. Helium is a rare gas with small density and high heat transfercoefficient. It can be used as a cooling and protective gas for LED filament lamp. In this paper, we investigated the effects ofhelium on the heat dissipation and luminescence performance of the A60 LED filament lamps by detecting the changes ofjunction temperature, color temperature, and luminous flux of different ratios helium inflating in the different power A60 LEDfilament lamps. Through the experiment, we found the most cost-effective ratio of helium gas in the A60 LED filament lampswithout improving the lamp size and the filament diameter.
1. Introduction
The LED filament lamp has both the appearance of thetraditional incandescent lamp and the higher photoelectricconversion of LED lamp. In 2008, Ushio Lighting introducedthe first LED filament lamp [1]. Panasonic described a flatarrangement with modules similar to filaments in 2014 [2].Unfortunately, the products did not gain widespread marketacceptance due to the poor thermal dissipation and luminousflux. This paper investigates the heat dissipation to increasethe luminescence of LED filament lamp. The LED filamentlamp was usually made up of chips, transparent substrate,and phosphors [3]. According to the development of sub-strate materials, LED filament lamps have undergone threegenerations from transparent ceramics, quartz glass tosapphire [4, 5].
Although the LED filament lamp has the basic structuresimilar to the traditional incandescent lamp, its luminousstructure is essentially different from the incandescent lamp.The incandescent lamp relied on the tungsten filament toemit visible light at high temperature, while the LED filamentlamp relied on filaments of the LED. However, because thephosphor completely wrapped around the filament, the heatdissipation effect of the filament was limited [6], which
was also the main reason to restrict the high power ofLED filament lamp [7].
Besides the lamp size, the filament phosphor diameter,and ionic wind [8, 9], this paper mainly explored the applica-tion of helium inflating to enhance the heat dissipation effectof LED filament lamp. As the helium is one of the inert gases,with its low density and high thermal conductivity, it wasvery suitable to be used to extract heat from the LED fila-ments [10, 11]. In this paper, the influence of helium on theheat dissipation and luminous performance of LED filamentlamps was explored by detecting the change of the tempera-ture and luminous flux of different helium ratios at the A60LED filament lamps with different power.
2. Experimental and Theoretical Details
2.1. Thermal Conductivity of Helium. This paper explored theheat dissipation and luminescent properties of LED filamentlamps filled with helium. Helium is a colorless and tastelessinert gas. Under normal pressure and temperature, thedensity of helium is 0.178 g/L. The helium molecule is verysmall and is just placed behind the hydrogen with the smal-lest density. As shown in Table 1, the thermal conductivityof helium is 0.144W/(m·°C) which is a little smaller than
HindawiInternational Journal of PhotoenergyVolume 2019, Article ID 6292036, 5 pageshttps://doi.org/10.1155/2019/6292036
the thermal conductivity of hydrogen 0.163W/(m·°C). As aninert protective gas, helium does not react with the materialin the LED filament lamp. In Table 1, the thermal conductiv-ity of helium is higher than argon, neon, oxygen, nitrogen,and air. This was the reason why helium was chosen for heatdissipation and gas protection.
2.2. Convective Heat Dissipation Mechanism of the A60 LEDFilament Lamp. The A60 LED filament lamp was the spher-ical shell with a maximum diameter of 60mm, as shown inFigure 1. In our experiment, the power values of the A60LED filament lamps were 4W, 7W, and 8W. The chips werespot welded in series on the holder of filament to form theLED filament. The holders of the filament and LED filamentare shown in Figure 2. These four LED filaments were inseries to form the A60 LED filament lamp. A linear drivewas provided in the lamp holder to support a stable currentinput for the LED lamp. The driving currents of 4W, 7W,and 8W in the A60 LED filament lamps were 13.5mA,22mA, and 25mA, respectively.
In the whole lamp, the heat is transferred from theLED filament to the helium when the helium is passingthrough the LED lamp in the high-temperature work.The density of the heating helium is smaller than thehelium at the low temperature, so the expansion rises.And the heat is transferred to the glass shell from the fila-ment, and then the next cycle starts. In the whole process,gas heat conduction followed Fourier law [12]. This phe-nomenon is affected by the natural factors of the fluid itself.When applied to fluid cooling, convection calculation isshown as follows:
Q = hAΔT 1
Among them, Q is the convection heat dissipation (theunit is W), and h is the thermal conductivity (the unit isW/m·°C). A is an effective heat transfer area. The tempera-ture difference between the heat transfer surface and thefluid is ΔT . The Fourier law can be applied to the convec-tion heat transfer process. In the process of heat convectionin the lamp, according to equation (1), the thermal conduc-tivity is the key factor affecting convective heat transferunder the condition of the same temperature differenceand the same area.
2.3. The Effect of Chip Junction Temperature on thePerformance of LED. The relationship between the mainwavelength of LED filament lamp and the junction tem-perature of the chip is shown as follows:
λ0 T = λ0 T0 + ΔT × 0 2 nm/°C 2
Table 1: Thermal conductivity of several common gases.
Gas Hydrogen Helium Argon Neon Oxygen Nitrogen Air
Thermal conductivity (W/(m·°C)) 0.163 0.144 0.018 0.049 0.024 0.023 0.023
(a)
104±
2
60±1 (mm)
(b)
Figure 1: (a) The A60 LED filament lamp and (b) its structure parameters.
Figure 2: (a) Holder of the filament and (b) LED filament in theA60 lamp.
2 International Journal of Photoenergy
In equation (2), λ0 T and λ0 T0 are the mainwavelengths of the emitted light at T and T0, respectively.ΔT is the temperature difference, that is to say the mainwavelength of the chip changed correspondingly with thetemperature difference, thus changing the spectral compo-sition of the chip [13]. The increase of the junction tem-perature also affected the color temperature of the LEDfilament lamp, making the color temperature drift. Thelifetime of LED chip increased exponentially with thedecrease of the junction temperature. When the temperatureof the chip rises from 40°C to 50°C, the life span of the chipcould be shortened from 42,000 hours to 18,000 hours[14]. In this paper, through the influence of helium onthe heat dissipation, luminescence performance and colortemperature of the A60 LED filament lamps were exploredby detecting the change of the junction temperature andluminous flux in the A60 LED filament lamps with dif-ferent powers.
2.4. Testing Measurements. The instrument LEDT300/H wasspecially designed and developed for measuring the junctiontemperature of LED filament lamps. The main test methodwas to put the test lamp in the chamber of the LEDT300B/Hand then connected the thermocouple with the current inputline of the lamp to test the junction temperature. That wasbecause the junction and the current input line connecteddirectly, the temperatures between them were the same.When the lamp was working in the normal working voltagerange, the exact value of the working voltage was obtainedwhen it reached the stable state, and the junction temperatureof the lamp in the stable operation was obtained by com-bining the value of the voltage temperature coefficient.
The spectrum integration sphere PMS-80 was mainlyused to test the photoelectric parameters of the LED filamentlamps. The working way of the integral ball was to placethe test light source or lamp in the center of the integralball. After applying the working voltage, the light wasreflected multiple times on the inner wall of the integratingsphere and finally concentrated on the window hole. Theexternal connecting device of the integrating sphere con-centrated the light at the window hole and finally calculatedthe photoelectric parameters of the test light source or thelamp, which included the parameters of luminous fluxand color temperature.
3. Results and Discussion
The positive chip mode was used in the A60 LED filamentlamps to meet the process stability in this experiment. Thetransparent ceramic substrate was used to improve theirperformance price ratio in this lamp. The A60 LED filamentmet the European state standard. The A60 LED filament witha power of 4W had a size of 38mm × 1 5mm, with 24 LEDchips in series. The LED filaments with the powers of 7Wand 8W both had the sizes of 50mm × 1 8mm, containing25 LED chips in series inside. The difference between themwas the power of the internal LED chips. The followingfigures are about the junction temperature and luminousproperties of the A60 LED filament lamps (powers of 4W,
7W, and 8W) under different helium inflating quantities(50%, 60%, 70%, 80%, and 90%) with the different pressuresranged from 0.5 Pa to 0.9 Pa. The junction temperature,luminous flux, and color temperature data diagram weretested at room temperature of 25°C.
3.1. Influence of Different Helium Inflating Ratios on theJunction Temperature of the A60 LED Filament Lamps. Itcan be seen from Figure 3 that with the increase of heliumgas inflating, the junction temperature of all the A60 LEDfilament lamps decreased. For the 8W power LED filamentlamp, the lowest helium inflating ratio of 50% got the highestjunction temperature of 113.5°C. In the same inflated heliumproportion, the 4W filament lamp had the lowest junctiontemperature. This was because the power value of 4W waslower, the working current was smaller, and the heat alsoreduced accordingly. Compared with the A60 LED filamentlamp with different power charge, the higher inflating ratiowas conducive to the heat dissipation of the filament andthe junction temperature.
In Table 2, the A60 LED filament lamps were drivenunder the power 4W and the voltage 270V. Compared withthe LED filament lamps of 4W power, the A60 LED filamentpowers and junction temperatures of 7W and 8W obviouslyreduced. Because the substrate size of the 7W and 8W powerfilaments was much larger than the 4W power filament, theheat dissipation was faster. The 7W and 8W power filamentshad the length of 50mm, while the 4W power filament had
50 60 70 80 9090
95
100
105
110
115
Ratio of helium gas (%)4W7W8W
Tem
pera
ture
of j
unct
ion
(°C)
Figure 3: Junction temperatures of the A60 LED filament lamps(4W, 7W, and 8W) with different helium inflating ratios.
Table 2: A60 LED filament lamp junction temperatures andfilament lamps under 4W-driven power.
Lamp type/W 4 7 8
Junction temperature/°C 92.40 79.9 69.12
Filament power/W 3.807 3.55 3.445
3International Journal of Photoenergy
only 38mm. Apart from that, the heat exchange area of4W power filament was smaller. Therefore, both thehelium gas inflating and the size of filament influencedthe heat dissipation.
3.2. Influence of Different Helium Inflating Ratios onLuminous Flux of the A60 LED Filament Lamps. Figure 4 isthe luminous flux data of the three different power A60LED filament lamps under different ratios of helium inflat-ing. For the same power level, the luminous flux increasesas the ratio of helium inflating increases. It can be explainedby the fact that the junction temperature decreases with thehelium inflating ratio.
In this experiment, we found that with 80% helium inflat-ing, the luminous flux of the A60 LED filament lamps were480 lm, 815 lm, and 1070 lm for the power values of 4W,7W, and 8W, respectively. These values were higher thanthe nominal luminous flux of the commercial A60 LEDfilament lamps of 470 lm, 806 lm, and 1055 lm also for thepower values of 4W, 7W, and 8W, respectively. At the valueof 80% helium gas inflating, these series of the A60 LED fila-ment lamps can maintain the nominal luminous flux valuerequirement, saving more energy than the lamp with heliumratio of 90% and improving the performance price ratio.
3.3. Influence of Different Helium Inflating Ratios on theColor Temperature of the A60 LED Filament Lamps.Figure 5 shows the color temperature of the three powerA60 LED filament lamps at different helium inflating ratios.The inflating ratio affected the junction temperature of thefilament, and the junction temperature affected the colortemperature change. From the data, it can be seen that thecolor temperature of the A60 LED filament lamp of everypower decreased with the increase of the inflatable ratio,which was in accordance with equation (2) that the temper-ature of the filament affected the color temperature ofthe filament. Of course, the main factor determining thecolor temperature of LED filament was the ratio of blueand yellow phosphor.
4. Conclusions
From the experimental analysis, it was found that the higherhelium inflating ratio had a significant effect on the heatdissipation and luminous properties of the A60 LED fila-ment lamps. In the case of low helium inflating ratios,the increase of helium volume can brought obvious perfor-mance improvement. The direction for the improvement ofLED filament lamp is to develop high-power LED filamentlamps. The greater power value means that the filamentneeds to carry higher current, leading to higher junctiontemperature. The high junction temperature had a heavyinfluence on the luminous flux, color temperature, and lifeof the A60 LED filament lamp. Therefore, the thermal analy-sis of LED was very important for judging the feasibility ofLED filament lamps. A good balance between luminous fluxand helium inflating volume helped enterprises to reduce thecost of LED filament lamps and improve their performance.In our research, we found that with 80% of helium inflating
without changing the size of the lamp and filament, theA60 LED filament lamp can maintain the nominal luminousflux value requirement. Consequently, it can reduce morecosts than a lamp with helium ratio of 90% and improvesthe performance and market competitiveness of the A60LED filament lamp with different power values.
Data Availability
The data used to support the findings of this study areincluded within the article.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
50 60 70 80 90400
500
600
700
800
900
1000
1100
4W7W8W
Lum
inou
s flux
(lm
)
Ratio of helium gas (%)
Figure 4: Luminous flux changed with different helium inflatingratios in the A60 LED filament lamp.
50 60 70 80 902720
2760
2800
2840
2880
Colo
r tem
pera
ture
(K)
Ratio of helium gas (%)4W7W8W
Figure 5: Color temperature changed in the A60 LED filamentlamps of different helium inflating ratios.
4 International Journal of Photoenergy
Acknowledgments
The authors greatly appreciate the support of the KeyLaboratory of Optoelectronic Materials and Applications inGuangdong Higher Education (No. 2017KSYS011), theKey Platform Construction Center Project in GuangdongDepartment of Education (No. GCZX-A1411), and theYouth Fund Project in Wuyi University (No. 2015zk13).The authors appreciatively acknowledge discussions withand manuscript editing by Prof. Norbert Willenbacher andPh.D. candidate Bruna R. Maciel at Karlsruhe Institute ofTechnology in Germany.
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