J. Mod. Phys., 2010, 1, 196-199
doi:10.4236/jmp.2010.13029 Published Online August 2010 (http://www.scirp.org/journal/jmp)
A Cooling System with a Fan for Thermal Management of
High-Power LEDs
Ruishan Wang1,2, Junhui Li1,2,3
1School of Mechanical and Electronical Engineering, Central South University, Changsha, China
2Key Laboratory of Modern Complex Equipme nt Desi g n an d Extr eme Manufacturing,
Ministry of Education, Changsha, China
3State Key Lab of Digital Manufacturing Equipment & Technology, Wuhan, China
Received May 27, 2010; revised July 18, 2010; accepted July 30, 2010
Abstract
To improve the heat dissipation of high-power light-emitting diodes (LEDs), a cooling system with a fan is
proposed. In the experiment, the LEDs array of 18 W composed of 6 LEDs of 3 W is used and the room tem-
perature is 26ºC. Results show that the temperature of the substrate of LEDs reaches 62ºC without the fan,
however, it reaches only 32ºC when the best cooling condition appears. The temperature of the LEDs de-
creases by 30ºC since the heat produced by LEDs is transferred rapidly by the fan. The experiment demon-
strates that the cooling system with the fan has good performance.
Keywords: High-Power Leds, Cooling System, Heat Dissipation, The Fan, Data Acquisition Card
1. Introduction
Light emitting diodes (LEDs), generally used for indicator
lights, have been developed for the past 50 years. Recently,
with the emerg ence of high po wer LEDs, they are receiv ed
more and more attention, and have begun to play an im-
portant role in many applications. Typical applications
include back lighting for cell phones and other LCD dis-
plays, interior and exterior automotive lighting including
headlights, large signs and displays, signals and illumina-
tion, traffic lights, spot lights, and so on [1,2].The extensive
applications are due to the distinctive advantages towards
incandescent lamp and daylight lamp, such as high bright-
ness, small size, ease of integration, anti-mechanical dam-
age, all solid-state, environmental protection, lower power
cost, long life, and high efficiency, good reliability, vari-
able color, etc. So, LEDs are called the fourth generation
light or green light [3,4], and have been foreseen as an “ul-
timate lamp” for the future [5]. However, based on the
current semiconductor manufacture technology, only 5%-
10% of the input power will transfer into light energy, the
remainin g will transf er into he at while the ch ip size i s only
1 × 1 mm-2.5 × 2.5 mm, the heat flux is very high. If the
heat can not dissipate in short time, it will lead excessive
temperature, shorten the life, and thermal stress will dam-
age the LEDs chip. So, effective thermal management is
the critical factor for the efficiency, reliability, and life of
LEDs, especially for high power LEDs, thermal manage-
ment has become the development bottleneck of LEDs
[6-8].
To address the thermal problem of LEDs, many investi-
gators have researched in terrelated ther mal management of
LEDs:
LUO and LIU [9] proposed a closed microjet cooling
system for LEDs thermal management. By optimizing the
microjet array device’s parameters, the cooling system was
used for cooling a 220 W LED lamp, and the temperature
tests demonstrate it can effectively cool the total system.
Zhang et al. [10] used MWNT and carbon black to im-
prove the thermal performance of TIM in high-brightness
light emitter diode (HB-LED) packaging. Thermal inter-
face material was developed to achieve the thermal con-
ductivity of about 0.6 W/m·K with 2 wt% nitric acid
treated CNT and 10 wt% carbon black. The output light
power of the 1 × 1 mm 2 HB-LED device with the devel-
oped TIM can achieve 62 mW with the input current of
300 mA. Yuan et al. [11] described a process of applying a
FEA technique to simulate and analyses a light emitting
diode (LED) array integrated in microchannel cooler mod-
ule. The cooling module with different internal configura-
tions, heat source density, and heat dissipation capacity
corresponding with different flow velocity are investigated.
From the analysis, the special design of internal staggered
fins in microchannel cooler could reduce the average die
temperature, the difference in temperature and the flow
resistance compared to straight fins in microchannel cooler.

R. S WANG ET AL. 197
Liu et al. [12] introduced a method of thermal design and
module of thermal resistance of High-power LED; and
describes heat dissipation design for illumination High-
power LED arrays. The results proved that the radiator
designed can control the maximum junction temperature of
LED chip within 70 under the condition that all chips ℃
work in full- lo a d an d the envir onment temp er ature is 40. ℃
Zhang et al. [13] studied the effect of thermal conductive
coating on the thermal management of LED lamps with
different color and packing number used in a close un-
der-water environment. Experiment result shows that the
thermal conductive coating used on LED integrated circuit
board can increase the thermal release efficiency of LED.
And the higher the thermal conductivity is, the better the
effect of thermal management is.
In this paper, a cooling system with a fan is proposed.
Several conditions at different input power of the fan are
conducted to investigate its effect on thermal management
of high power LEDs. For achieving relatively exact tem-
perature in LEDs, a K-type thermocouple is welded into
the substrate of LEDs, and its signal is collected by using
data acquisition system. Based on the detected temprature,
the cooling ability of the system is evaluated.
2. Experimental
Figure 1 demonstrates the cooling system. It composes
of a radiator including cooling fins and a fan. In the sys-
tem, the LEDs and cooling fins is connected through
thermal conductive silicone grease. It can be seen that
the system is very simple and convenient, and the room it
required is very small.
The light source module is composed of six LEDs in
tandem mode. (The LED, which type is XL-HP3WHWC,
the diameter of substrate is 20 mm, the emitted color is
white, and the limit power is 3 W). The total power con-
sumption of the 2 × 3 array is added up to be 18 W. The
radiator is 80 mm × 95 mm. The fan’s model is 3110KL-
04W-B50. The temperature of heat dissipation substrate
of LEDs is measured by K-type thermocouple, the mea-
surement error of which is about 0.5ºC at the temperature
range from –30ºC to 150ºC.
Experimental system is constructed as shown in Fig-
ure 2 DC power supply of LEDs is special electrical
source of LEDs, and its power is 6 × 3 W = 18 W. In the
experiment, the junction temperature could not be
achieved directly, so, the substrate of LEDs is measured.
Although there is difference temperature between the
heat dissipation substrate of LEDs and the junction tem-
perature, it is feasible using the former to check the
cooling ability of the proposed concept since it can re-
flect the latter intuitively. At the beginning, in order to
study the heat dissipation effect of the fan, a couple of
comparative experiments are conducted under the condi-
tion without the fan and the input power of the fan is
Figure 1. The cooling system.
Figure 2. The experimental system.
2.13 W respectively. Then, a set of experiments are con-
ducted to study the effect of different inpu t power of the
fan on the thermal management of high-power LEDs.
In the experiment, a temperature transmitter is u sed to
transform the signal of temperature from the thermocou-
ple into that of voltage which can be acquired by using
the data acquisition card (PCI-1710). The acquisition
frequency is 0.1 s. Then, the signal of voltage is trans-
formed into the signal of temperature through the for-
mula describing the relationship between the temperature
and the voltage. After the signal o f temperature is filtered
with the software of MATLAB, the temperature graph
can be found which demonstrates the cooling effect of
the system.
3. Results and Analysis
After the signature of temperature is filtered with the
software of MATLAB, the temperature graphs of LEDs
are found as follows:
3.1. Without the Fan and the Input Power of the
Fin is 2.13 W
Figure 3 shows the temperature variations of substrate of
LEDs with time without the fan and at the input power of
the fan 2.13 W. It can be seen that the temperature of
substrate of LEDs increases continuously up to 62ºC and
still has a rising trend without the fan, however, it reach-
es the maximum about 32.5ºC in short time and remains

R. S WANG ET AL. 198
Figure 3. The temperature variations of substrate of LEDs
with time without the fan and at the input power of the fan
2.13 W.
steady by using the fan. The above result is easy to un-
derstand that the heat generated by LEDs conducts to the
cooling fins, if the heat of cooling fins does not released
into the environment in time, the temperature of LEDs
will increases continually. In the designed system, the
main approach of heat exchange between the system and
environment is natural convection though cooling fins
when the fan is not used. However, when the fan works,
it is forced convection, and the effect of heat exchange
will be effectively improved. This indicated that the fan
has a good performance on the thermal management of
high-power LEDs.
3.2. The Different Input Power of the Fan
Figure 4 shows the temperature variations of substrate of
LEDs with time at different input power of the fan. It can
be seen that the temperature of substrate of LEDs will
reach a steady value within 5 mins when the fan is used,
and the steady temperatures are different with the differ-
ent input power of th e fan. The ma ximum a nd mini mum
Figure 4. The temperature variations of substrate of LEDs
with time at different input power of the fan.
temperature is 35.6ºC and 32ºC when the input power is
0.23 W and 3.22 W respectively. The higher the input
power is, the lower the steady temperature is. As the en-
largement of input power, forced convection enhanced,
fluid can quickly remove LED heat, leading to the lower
temperature of the substrate of LEDs, while the running
cost is correspondingly increased. In the practical appli-
cations based on the above experiment, a choice should
be made to achieve a balance between the cooling effect
and the power consumption of the system. Figure 4
shows that 0.83 W and 1.2 2 W of the system is appropr i-
ated.
4. Conclusions
A cooling system with a fan is presented to improve the
heat dissipation of high-power LEDs. Several conditions
at different input power of the fan are conducted. The
experimental result demonstrates that the cooling system
with the fan has a good performance on the thermal
management of high-power LEDs. The minimum tem-
perature is only 32ºC when the fan is applied and the
environment temperature is 26ºC, while it reaches 62ºC
without the fan. With the increasing of the input power,
however, the cooling performance improves slightly, so,
in practical applications, appropriate input power should
be selected to achieve a good balance between the cool-
ing effect and the power consumption of the system.
5. Acknowledgements
This work was supported by National Natural Science
Foundation of China (No. 50975292, 50705098), the
China High Technology R & D Program 973 (No. 2009
CB724203), Hunan Natural Science Foundation of China
(No. 07JJ3091), State Ke y Lab of Digital Manufacturing
Equipment and Technology of China (No. 2007001),
National S & T Major Project of China (No. 2009ZX020
38), and Program for New Century Excellent Talents in
University (No. NCET-08-0575).
6. References
[1] W. H. Chi, T. L. Chou, C. N. Han and K. N. Chiang,
“Analysis of Thermal Performance of High Power Light
Emitting Diodes Package,” International Conference on
Electronics Packaging Technology, Nanjing, 2008, pp.
533-538.
[2] X. Luo, W. Xiong and S. Liu, “A Simplified Thermal
Resistance Network Model for High Power LED Street
Lamp,” International Conference on Electronic Packag-
ing Technology & High Density Packaging, Shanghai,
2008, pp. 1-7.
[3] B. Li, “Lumen Efficiency of 1 W-Level High Power
White LED,” Semiconductor Optoelectronics, Vol. 26,
No. 4, 2005, pp. 314-316.

R. S WANG ET AL. 199
[4] X. He, B. Cheng, L. Yin and J. Zhang, “Testing System
for Thermal Resistance of High-Power LED,” Electronic
Measuremient Technology, Vol. 31, No. 9, 2008, pp. 17-
20.
[5] N. Holonyak, “Is the Light Emitting Diode (LED) an
Ultimate Lamp?” American Journal of Physics, Vol. 68,
No. 9, 2000, pp. 864-868.
[6] W. Dai, J. Wang and Y. Li, “Transient Thermal Analysis
of High-power LED Package,” Semiconductor Optoelec-
tronics, Vol. 29, No. 3, 2008, pp. 324-328.
[7] B. Yu and Y. Wang, “Junction Temperature and Thermal
Resistance Restrict the De veloping of High-power LED,”
Chinese Journal of Luminescence, Vol. 26, No. 6, 2005,
pp. 761-766.
[8] N. Narendran and Y. Gu, “Life of LED-Based White
Light Source,” IEEE/OSA Journal of Display Technology,
Vol. 1, No. 1, 2005, pp. 167-171.
[9] X. Luo and S. Liu, “A Microjet Array Cooling System for
Thermal Management of High-Brightness LEDs,” IEEE
Transactions on Advanced Packaging, Vol. 30, No. 3,
2007, pp. 475-484.
[10] K. Zhang, G. Xiao, C. Wong, H. Gu and B. Xu, “Study
on Thermal Interface Material with Carbon Nanotubes
and Carbon Black in High-Brightness LED Packaging
with Flip-Chip Technology,” 55th Electronic Compo-
nents and Technology Conference, Lake Buena Vista,
2005, pp. 60-65.
[11] L. Yuan, S. Liu, M. Chen and X. Luo, “Thermal Analysis
of High Power LED Array Packaging with Microchannel
Cooler,” 7th International Conference on Electronic
Packaging Technology (ICEPT '06), Shanghai, 2006, pp.
1-5.
[12] Y. Liu, G. Fu, C. Gao, X. Li and S. Wang, “Thermal
Analysis of Illumination High-Power LED,” Chinese
Journal of Electron Devices, Vol. 31, No. 6, 2008, pp.
1716-1719.
[13] S. Zhang, L. Fang, G. Fu, X. Tan, J. Dong, Y. Chen and
L. Gao, “Effect of Thermal Conductive Coating on Ther-
molysis Property of LED,” Semiconductor Optoelectron-
ics, Vol. 28, No. 6, 2007, pp. 793-796.