Optical and thermal design of light emitting diodes omnidirectional bulb

Zhi Ting Ye; Hao-Chung Kuo; Cheng-Huan Chen

doi:10.1364/AO.54.000E94

Applied Optics
Vol. 54,
Issue 28,
pp. E94-E101
(2015)
•https://doi.org/10.1364/AO.54.000E94

Optical and thermal design of light emitting diodes omnidirectional bulb

Zhi Ting Ye, Hao-Chung Kuo, and Cheng-Huan Chen

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Zhi Ting Ye, Hao-Chung Kuo, and Cheng-Huan Chen, "Optical and thermal design of light emitting diodes omnidirectional bulb," Appl. Opt. 54, E94-E101 (2015)

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Abstract

The penetration of LED light bulbs into the lighting market is growing quickly in recent years due to significant increase of LED efficiency and reduction of cost. One major issue to be improved is the overall light bulb efficiency, which can fulfill “Energy Star for Lamps” while keeping sufficiently high efficiency. The efficiency issue results mainly from the high directionality of the LED sources and the corresponding solutions to make the emission more diverse. In this paper, a diffusion white reflection sheet (DWRS) with an array of holes is proposed as a high efficiency solution for modulating a light emission profile with SMD type LED source. The hole size is adjusted with fixed hole pitch to both maximize the efficiency and meet the omnidirectional specification. In addition, the concept of thermal plastic insertion molding metal is proposed for thermal management without fins for cooling. The prototype demonstrates the efficiency (Ef.) of 87.6% and LED pad temperature of 85°C, which shows the feasibility as a total solution for high efficiency LED omnidirectional bulbs.

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	Specifications
Components	Surface Characteristics	Material
Lampshade top	Transmissive diffusion	PC $in dex = 1.59$ Bulk scatter: Human uterus Tissue Anisotropy $(g) = 0.69$ Scatter Coefficient (1/mm) $= 39.4$
Diffusion White Reflection Sheet	Transmissive diffusion	Absorptance: 10% Integrated BRDF: 90% BRDF A: 0.315126; BRDFB: 0.1
Lamp Shade bottom	Transmissive diffusion	PC $index = 1.59$ Bulk scatter: Human uterus Tissue Anisotropy $(g) = 0.69$ Scatter Coefficient $(1 / mm) = 39.4$
MCPCB (Metal Core PCB)	Absorptance: 30% BRDF: 67%	Al
Heat Sink	Absorptance: 100%	Al and Nylon
E26	Absorptance: 100%	Al

Parameter	Value
A	3.50047
B1	−0.03118
B2	0.00535
B3	−9.58551E-4
B4	3.83036E-5
B5	−4.61321E-7

Holes Size Diameter (mm)	Light Efficiency (%)	Meet “Energy Star for Lamps” Standard (Y or N)
2	85.8	N
2.5	87.8	N
3	89.5	N
3.5	93.8	N
Adjusted from 3.5 to 2 mm	88.3	Y

Conditions	Specification Values	Actual Value	Pass or NG
The lamp (polar) axis in maximum increments of 22.5° from 0 to 180°	$< 22.5 °$	$< 22.5 °$	pass
Measured intensity values may by no more than 25% from average value from 0 to 135°	$< 25 %$	19.9%	Pass
	$< 25 %$	9.7%	Pass
At least 5% of total flux (l m) in 135 to 180° zone	$> 5 %$	11.6%	pass

Component	Material	Thermal Conductance K	Radiant Emissivity Coefficient
Lamp shade	PC	0.25 W/(m*K)	0.9
DWRS	PET	0.25 W/(m*K)	0.9
Light board	MCPCB	$Y = 3 W / (m * K)$	0.9
Light board	MCPCB	$X = 200 W / (m * K)$ $Z = 200 W / (m * K)$	0.3
Insertion molding metal	AL-1050	200 W/(m*K)	0.3
Thermal plastic	Nylon base	1.3 W/(m*K)	0.9
E26	ADC-12	96 W/(m*K)	0.3

Measuring Point (at 10 W $Ta = 26 °C$ )	Thermal Plastic Insert Molding Metal Base Temperature (°C)
LED pad	85.56
The top point of cooling part	78.81
The middle point of cooling part	77.80
The bottom point of cooling part	75.84

Condition (Normalized)	CCT (K)	Ra	Watt (w)	Luminous Flux (lm)	Ef. (%)
LED light source	3111	83	9.4	880	100
Omni-directional bulb complete module	3058	83	9.4	771	87.6

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Applied Optics