International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8668-8672
© Research India Publications. http://www.ripublication.com
Thermal Performance and Light Distribution Improvement of a
Lens-Attached LED Fog Lamp for Passenger Cars
W. S. Sim1 and Y. L. Lee2*
Department of Mechanical Engineering, Graduate school, Kongju National University, Korea.
1
Department of Mechanical and Automotive Engineering, Kongju National University, Korea.
*Corresponding Author
2
than 60 to 70% of input power into heat, and the junction
temperature increases with power supply [6].This increase in
junction temperature is known to be a cause of reduced optical
power. Chip failure also occurs when the junction temperature
exceeds 150℃, thus severely shortening the LED lifespan [7].
Many studies have been conducted to improve the heat
dissipation performance of LEDs. Sökmena et al. [8]
optimized the heat dissipation performance of a cylindrical fin
type heatsink at various temperatures. Kim et al. [9] applied
copper oxide (CuO) to an aluminum-alloy heatsink to improve
the heat dissipation performance by enhancing thermal
radiation emission. Wang et al. [10] improved the heat
dissipation performance of LED headlamps through the heat
dissipation analysis of a heatsink combined with heat pipes.
Figure 1 shows the light distribution patterns of a halogen fog
lamp and a regular LED fog lamp. Since the light distribution
pattern of LED fog lamps are easily distinguished from that of
halogen fog lamps, it is not possible to achieve the same light
distribution as the latter without introducing a light
distribution lens. The light distribution of light from the LED
lamp has a large area, causes glare in drivers’ eyes, and has
poor intensity in certain areas. In order to use LED fog lamps,
such issues must be resolved.
This study seeks to develop a 10W LED fog lamp that has the
same light distribution performance as a halogen fog lamp.
Heatsink optimization was carried out to enhance the heat
dissipation performance, and a light distribution lens was
introduced to improve the light distribution. Heat dissipation
analysis was performed to optimize junction temperatures for
various heatsink shapes, and light distribution analysis was
used to improve the shape of the light distribution lens and
reflector.
Abstract
Halogen light sources, which have seen significant
developments since the invention of the tungsten filament
lamp in 1916, are beginning to be replaced by LED light
sources. The purpose of this study was to develop a 10W LED
fog lamp that has the same light distribution performance as a
halogen fog lamp. Heatsink optimization was carried out to
enhance heat dissipation performance, and a light distribution
lens was introduced to improve light distribution. The analysis
showed that the 16 board-fin type heatsink had the best heat
dissipation performance. In addition, the lens-attached LED
fog lamp exhibited a similar light distribution performance to
that of a halogen fog lamp.
Keywords: Fog lamp, light distribution lens, light emitting
diode, heatsink, junction temperature
INTRODUCTION
Halogen, the most widely used light source in automobiles,
relies on light emitted during thermal radiation by the tungsten
filament when the current passes through a lamp filled with
halogen and a noble gas. Halogen lamps involve a simple
mechanism and produce natural-looking light, but 95% of
energy is released as heat and only the remaining 5% is
converted into light. While luminous efficiency and color
temperature increase with heat, the filament continues to
evaporate and eventually breaks [1].As such, the
disadvantages of halogen include poor efficiency and a short
lifespan.
If fog lamps are produced with LED as a light source, the
small size of the LED chip will allow a 60 to 75% size
reduction compared to halogen fog lamps. Differentiated
designs are also possible through multi-chip modules [2].
LED lamps have a lifespan 100 times longer than halogen
lamps due to their smaller energy consumption [3]. Their fuel
consumption decreases by 19.5% when driving with lights on,
and CO2 emissions are lowered by 19.6% [4].
In 2007, Toyota and Lexus became the first cars to use LEDs
in low beam headlights [5]. Recently, Europe has attempted to
replace LED with halogen as a light source for not only
headlamps, but also fog lamps. In line with this trend, research
on LED fog lamps has become popular in Korea. Recent
developments in automotive lighting technology have led to
high brightness, low power, and high efficiency, as well as the
acquisition of characteristics suited to the lighting device.
While the aforementioned advantages can be achieved by
replacing halogen with LED fog lamps, LED converts more
(a) Halogen fog lamp
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8668-8672
© Research India Publications. http://www.ripublication.com
(b) LED fog lamp
Figure 1: Light distribution patterns of the halogen fog lamp
and LED fog lamp
NUMERICAL
METHODS
AND
LIGHT
DISTRIBUTION LENS
The LED fog lamp of this study was comprised of an LED
module, silicone mold, PCB, light distribution lens, and a
heatsink. Figure 2 shows the schematic diagram of the three
heatsinks used to enhance heat dissipation performance. The
three shapes used were the circular-fin type, cross-fin type,
and board-fin type, and they each had a heat dissipation area
of 0.0139m2. The flow was steady-state, three-dimensional,
and laminar, and thermal radiation was considered in the heat
dissipation analysis. Catia[11] was used for the geometric
modeling of the LED fog lamp, while Fluent [12] was
employed for the heat dissipation analysis. The heatsink shape
with the most outstanding heat dissipation was determined
through heat dissipation analysis before optimizing the
number of fins.
To attain the same light distribution performance as a halogen
fog lamp, this study introduced a light distribution lens, as
shown in Figure 3. The condensing section at the bottom
collects light, and the reflecting section at the top has been
treated with Ag non-reflective coating. The material of the
light distribution lens was assumed to be polycarbonate. Light
distribution analysis was performed on the LED fog lamp
equipped with the reflector [13] shown in Figure 4.
Figure 3: Schematic diagram of the polycarbonate light
distribution lens
Figure 4: Schematic diagram of the LED fog lamp reflector
(a) Circular-fin
(b) Cross-fin
(c) Board-fin
RESULTS AND DISCUSSION
Heat dissipation performance of the LED fog lamp
Figure 5 shows the junction temperature contours for the
different heatsink shapes when a power of 8W is applied to
the LED fog lamp. The results for all three shapes fell below
the limit of 120oC, and the board-fin type had the most
Figure 2: Three heatsink shapes considered for the LED fog
lamp
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8668-8672
© Research India Publications. http://www.ripublication.com
outstanding heat dissipation, followed by the circular-fin type
and cross-fin type. The board-fin type is not only the most
efficient in heat dissipation, but can also be easily mass
produced using serration techniques. For these reasons, the
board-fin type heatsink was selected for the purpose of this
study.
Figure 6 shows changes in junction temperature after a light
distribution lens is added to the LED fog lamp. The junction
temperature of the lens-attached fog lamp rose by 0.3oC to
109.2oC, which can be considered a negligible increase. As
such, we can see that the light distribution lens has no
significant influence on the heat dissipation performance of
the LED fog lamp.
(a) Circular-fin type
(a) Without the light distribution lens
(b) Cross-fin type
(b) With the light distribution lens
Figure 6: Changes in the junction temperature of the fog lamp
To further optimize the heat dissipation performance of the
lens-attached LED fog lamp, heat dissipation analysis was
performed while varying the number of heatsink fins. As
shown in Figure 7, we can see that the junction temperature of
the fog lamp decreases with an increasing number of fins. The
junction temperature rapidly declines at first, but the rate of
decrease becomes more gradual as the number of fins
continues to increase. The most outstanding heat dissipation
performance was attained when there were 24 fins. Compared
(c) Board-fin type
Figure 5: Temperature contours in relation to heatsink shape
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8668-8672
© Research India Publications. http://www.ripublication.com
Figure 10 shows the irradiance of the halogen fog lamp and
LED fog lamp. The results for irradiance are similar to light
distribution patterns. When a light distribution lens is attached,
the LED fog lamp exhibits a similar irradiance to the halogen
fog lamp due to the enhanced light distribution performance.
However, the irradiance of the LED fog lamp still has room
for improvement.
to the case of 16 fins, the area of heat dissipation expanded by
35%, while the junction temperature dropped by 0.3oC. The
weight of the fog lamp at 24 fins was also 10% heavier.
Although heat dissipation is better at 24 fins, the 16-fin
heatsink is more practical given the weight difference and
negligible decrease in junction temperature.
Figure 7: Changes in junction temperature with the number of
fins
(a)Halogen fog lamp
Light distribution analysis of fog lamp with reflector
Figure 8 shows the principle of light distribution when light
from the fog lamp bounces off the reflector. Light is refracted
since it moves sideways instead of going straight due to the
light distribution lens, and a suitable light distribution pattern
is achieved.
Figure 9 shows the light distribution patterns of the halogen
fog lamp and the LED fog lamp using the same reflector. The
halogen fog lamp has a long and thin pattern suitable for the
fog lamp, whereas the LED fog lamp has a pattern
concentrated in the center. Compared to the regular LED fog
lamp of Figure 3, the lens-attached LED fog lamp has a light
distribution performance closer to that of the halogen fog
lamp. The light distribution performance is expected to
improve further through the use of multi-face LED fog lamps.
(b)LED fog lamp
Figure 9: Light distribution patterns of the halogen fog lamp
and LED fog lamp
(a) Halogen fog lamp
Figure 8: Principle of light distribution for the LED fog lamp
with a reflector
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8668-8672
© Research India Publications. http://www.ripublication.com
[2]
[3]
[4]
(b) LED fog lamp
[5]
Figure 10: Irradiance of the halogen fog lamp and LED fog
lamp
[6]
CONCLUSION
This study performed heat dissipation and light distribution
analyses of an LED fog lamp in relation to the heatsink shape
and the attached light distribution lens. Through the analysis,
the heat dissipation performance of the 10W LED fog lamp
was optimized and the light distribution performance
improved. The conclusions derived in this study are as follows:
1.
The LED fog lamp with the 16 board-fin type
heatsink offers the most outstanding heat dissipation
performance. In addition, the board-fin type is
suitable for mass production.
2.
When a light distribution lens is introduced to
improve light distribution performance, the junction
temperature remains almost the same, and the heat
dissipation performance is also satisfactory. Here, the
junction temperature is approximately 10.8oC lower
than the limiting temperature.
3.
The lens-attached LED fog lamp showed an
improved light distribution performance compared to
the regular LED fog lamp. However, to achieve the
same light distribution performance as the halogen
fog lamp, further improvements such as the use of
multi-face LED fog lamps are needed.
To enhance light distribution performance, optimization
studies can be performed on variables such as the position and
number of LED modules and LED chip arrangement.
ACKNOWLEDGEMENT
This study was supported by a grant of the SME R&D project
for the Start-up & Grow stage company. Small & Medium
Business Administration. (S2333652)
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