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### Author Topic: Calculate how far light beam can travel in air  (Read 971 times)

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#### airman00

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##### Calculate how far light beam can travel in air
« on: May 28, 2009, 10:40:49 AM »
I have an IR led with a radiant intensity of 19mW. Wavelength of 950nm. How do I calculate how far the beam will travel in air before becoming really weak.
basically how can I calculate the intensity of the IR light over air per distance?
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#### guncha

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##### Re: Calculate how far light beam can travel in air
« Reply #1 on: May 28, 2009, 10:48:24 AM »
Light intensity drops off with inverse square of distance. Just like gravity and electromagnetic something. Don't remember the exact formula though. Anyway, if you have some amount of light at one meter (lux?), you'll have nine times less at three meters.

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##### Re: Calculate how far light beam can travel in air
« Reply #2 on: May 30, 2009, 12:07:28 PM »
It has a lot to do with the air: pressure, purity, humidity, temperature, etc.

Too many factors.

You'd do better running an experiment in a realistic situation, graphing it in excel, then extrapolating the data for the distance your curious about.

As guncha said, its probably roughly proportional to the inverse square of distance.