1. Electricity Consumers: LED Lighting
461 billion kW of energy goes toward lighting in the US
AHELI CHATTOPADHYAY, ARIEL MARBER, ZYGIMANTAS STRAZNICKAS

2. Background: What is an LED?
An LED includes an anode and cathode of opposite charges – a voltage is applied, which causes light to be given off; LED does this very efficiently

3. Advantages of LED Lighting
Ultra-long lifetime
No toxic mercury content
No UV or IR radiation
Small size
Digitally controllable
Fast-changing light intensity

4. LED Applications for a Home
Replace incandescent and fluorescent light bulbs in homes
Light sensors – responding to changing light levels
TV - more dynamic images
Outdoor lighting – for gardening

5. Problem
LED lighting tends to have a high junction temperature, or operating temperature.

6. Relationship Between Junction Temperature and Lifetime
Relative Light Flux
Decreasing the junction temperature leads to a significant increase in the bulb’s life time.
Lifetime
Junction Temperature 74 C
Junction Temperature 64 C

7. Light Flux vs. Junction Temperature
Relative Light Flux
Decreasing the junction temperature leads to a significant increase in the bulb’s emitted light flux. Energy saving for producing the same light flux is 20 % less
Junction Temperature (C)

8. Goal / Purpose
To increase LED efficiency by reducing LED junction temperature through the use of:
- aluminum nitride (AIN) substrate
- Phase-Change Material (PCM)
- aluminum heat sink

9. Why AlN? Laser AlN Al . AlN is not electrically conductive material
Laser
AlN
AlN is not electrically conductive material
When lasers hit the AlN, the nitrogen is removed, leaving behind the Al (laser evaporation of N)
A circuit can be drawn using the laser
The resultant circuit on the material can conduct both electricity and heat, as opposed to regular circuits which can conduct only electricity
Because they can conduct heat, they can absorb the heat released by the LED, thereby cooling the LED and allowing it to function at a lower junction temperature (prevents overheating) Al

10. Why Phase Changing Material?
PCMs use the heat given off by semiconductors to melt a solid to a liquid.
The melting point temperature is maintained as heat is added and the phase change occurs.
Heat released by LEDs goes towards changing the solid PCM to liquid, instead of towards a T change\
This also cools the LED and allows it to perform at a lower junction T

11. Why a Heat Sink?
A heat sink is a passive heat exchanger that cools a device by dissipating heat into surrounding air.
By releasing heat, a heat sink can accelerate the freezing process when liquid PCM turns back into solid PCM.
Heat sink releases excess heat into the air
This accelerates the process of turning liquid PCM back into solid
IMPROVES LED LIFETIME

12. Standard LED Cooling

13. Our Design: PCM-cooled LED Using AlN Substrate and Heat Sink

14. Efficiency Related to Cost
Paraffine PCMs, AlN, and Al come at low cost
Although these lights are more expensive, the high upfront cost is compensated by improvement of LED lifetime.
All three components might not be necessary to lower-power LEDs.

15. Conclusion
The use of AlN substrate, PCM cooling, and a heat sink in a single system can:
decrease the junction temperature of the LED
improve the lifetime of the LED
improve LED efficiency (by up to 20 %)
be economically feasible

16. References http://ledsmagazine.com/features/2/5/8
2010 Philips solid-state lighting solutions, Inc.
Evaluating Light Output Technical brief (Philips)
U.S. Department of Energy

17. Acknowledgements
A special thank you to the advisors, Dr. Mark Geller and Dr. Eli for their feedback and guidance.

18. PCM LED Cooling Parameters of the Led: Led power consumption is 80 W
Input voltage is 220 V
Junction temperature is 650C
Dimension is 370*285*195 mm
Typical parameters of the PCM material:
Melting point is 300C
Specific latent heat is 200 kJ/kg
Thermal conductivity is 0.3 W/m0C
Density is 850 kg/m3
Specific heat capacity is 2200 J/kg0C
The estimations were provided for NIBBE Led Model: NB- FDL02-80 of SHENZEN NIBBE TECHNOLOGY CO., LTD

19. Calculations The mass of the PCM equal:
m = ρ*V, where ρ is PCM density, V is PCM volume.
m = (.37*.285*.195)*850 = 17.5 kg
The input power P = 80*08 = 64 W (80% of the led power transforms to the heat).
The melting time of the PCM is:
t = 17.5*250000/64 = 19 hours
It means that in above mentioned case during 19 hours the temperature in the pcm material300C. The junction temperature can be easy estimated if we know the heat resistance junction to case:
Tj =Tc + P*R, where R is heat resistance in 0C/W, Tc is case temperature. For example if R = 0.1 0C/W the junction temperature will be 360C.
5 kg of PCM is needed for the LED to operate for 4.5 h