# light intensity and distance of color sensor

Discussion in 'The Projects Forum' started by thavamaran, Mar 3, 2009.

1. ### thavamaran Thread Starter Active Member

Feb 21, 2008
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Hi, im Thavamaran and currently in final year of my degree, so im using TCS230, its a CMOS color sensor whereby im doing various types of test. TCS230 output is frequency and its digital. so i was doing a test recently whereby i place my sensor about +-5cm from a surface, which the surface consists of a particular color paper.

So from 5cm when i slowly decrease to 4 cm ,3 cm and so on till i stick my sensor to the paper, the output frequency was slowly decreasing when the distance decrease. and when i increase my distance from 5cm, like say 6 cm and onwards, the frequency output increase.

Can i know why its characteristic is like that? what is the relationship between light intensity and distance?

PS: the illumination for the sensor was the fluorescent light in my lab, no external illumination.

2. ### KMoffett AAC Fanatic!

Dec 19, 2007
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Per the data sheet:
As you move the sensor closer the lighted surface appears brighter to the sensor. Think about the "inverse square law" of radiation.

Ken

Apr 20, 2004
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4. ### thavamaran Thread Starter Active Member

Feb 21, 2008
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Hey KMoffett, im sorry for bothering you, but i dont really know what is inverse square law of radiation, so can you explain to me in a least detailed way.

beenthere, thanks for the link, i went through it.

Thanks guys.

5. ### KMoffett AAC Fanatic!

Dec 19, 2007
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Google is always my friend and yours:
http://en.wikipedia.org/wiki/Inverse_square_law

Basically if you double the distance between the sensor and the light source (your colored paper), the intensity of the light will be reduced to 1/4th the initial intensity...1/(2x2). If you moved it three times the original distance, the sensed intensity would be only 1/9th the original intensity...1/(3x3). If you moved the sensor to only 1/2 the original distance the sensed intensity would be 4 times the original...1/(0.5x0.5).

Ken

Last edited: Mar 4, 2009

Apr 20, 2004
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