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Electronics/Science fair project on LEDs.

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Question
Dear ZZ, My name is Caleb. I am an 8th grader and I am doing a science fair project on how temperature effects the strength of LED. Do shifts in temperature effect how bright LED car headlights are? Such as the difference between the temperatures of Barrow, Alaska and the temperatures of Miami, Florida.

Answer
LED lamps or lights are temperature dependent; not only for light output but color.

As a general rule the cooler the junction of the LED the brighter the light output.  As the junction temperature increases the light output will reduce gradually.  If the junction temperature gets too high the LED may fail or the light output will drop to zero.  But, this high temperature is much higher than would be seen in automotive use.

The temperature of the LED diode junction is a function of the environment it is in and the current passing through it.  In an automobile it is housed or encased in a protection shell with the clear or translucent covering in the front for the passage of light out to the road.  The back portion on the inside of the housing is a curved reflective surface to reflect the illumination outward.  Therefore, there is some limitation of the extreme temperatures due to the covering around the LED lamp assembly and the heat of the engine.

It is my opinion that the amount of light output level or color change that might be cause by temperature variations between Alaska and Florida would not be substantial and perhaps not even visible to the naked eye.  In other words it would take greater variations in temperature to bring about noticeably visible changes.

Here is a rather technical treatise on LED characteristics but it will be interesting for you to glance through it. About 1/3 down is where temperature is discussed.

http://en.wikipedia.org/wiki/Light-emitting_diode

and here is a very good discussion about the use of LED headlamps in automobile applications. One section of interest is about using them in cold temperature climates; an external heater may be needed to melt the ice away from the front lens whereas filament based headlamps put out their own heat.  And so on.  Happy Reading:

http://www.ebay.com/gds/LED-Headlights-Buying-Guide-/10000000177633515/g.html


Hope this helps.

Good Luck with your project.

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Expertise

Electronics questions about AC, DC and digital theory.

Experience

Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

Organizations
IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

Education/Credentials
BSEE University of North Dakota

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