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light intensity and distance of color sensor

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thavamaran

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light intensity and distance

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.
 

what is intensity when speaking of color?

Think about what the sensor sees.
If you put it very near the paper, it sees a little square of (for example) white paper and this light (i mean the light that is reflected by the paper) is what the sensor measures. If you take it away, it sees a bigger square, so the light (i'm not sure if this is the correct word) is increased. Also you must consider what are you measuring, it's reflected light, if the square is bigger, then the light is bigger, right?. I'm not an expert, so maybe i'm wrong, but i'm pretty sure that the basic idea is right, i mean, it seems ok that it act in this way (¿or not?).

Regards, Diego.

Added: I think that this is true if the viewangle of the sensor is limited, if it is 180º then what i think is not true.
 

tcs230 example

[Added: I think that this is true if the viewangle of the sensor is limited, if it is 180º then what i think is not true.]

Hey diegobb, thanks for the reply, anyway i get your idea somehow, but what
actually u meant by the 180 degree in the above column. Please explain. thank
you. Thanks for your time dude.
 

distance of colors in light

thavamaran said:
[Added: I think that this is true if the viewangle of the sensor is limited, if it is 180º then what i think is not true.]

Hey diegobb, thanks for the reply, anyway i get your idea somehow, but what
actually u meant by the 180 degree in the above column. Please explain. thank
you. Thanks for your time dude.
Click to expand...

After searching for an image, i think that the correct term is "angle of vision", instead of "view angle". (I'm sorry, but i speak spanish, so sometimes i'm a little confused about some words)

I think with this image everything explains itself:
**broken link removed**

Also, i'm not sure that 180º is what i think it was. 90º is what was thinking about, see the attached picture.

Regards, Diego.
 

distance to see color

If you take it away, it sees a bigger square, so the light (i'm not sure if this is the correct word) is increased.
Click to expand...
Completely wrong, unfortunately. You may want to consult an optics text book to understand why.

I think, it's like this:
1. If the paper would be illuminated evenly
2. If the sensor angle of view doesn't exceed the paper area
3. If the illumination isn't affected by the sensor's shade or reflected light
then the frequency wouldn't change

Point 2 may be ensured, point 1 and 3 never can in a real setup. If you think, you're able to, kindly explain how you did it.

If you intend to operate the TCS230 as a color sensor, the uneven illumination always present in a real enviroment isn't an issue, cause you can measure relative spectral intensities by utilizing it's different channels. There's a rich offer of TAOSINC application notes, that tell how to.

P.S.: An additional remark regarding angular sensitivity. As the datasheet reveals, TSC230 has a directional characteristic similar to any flat detector without optics, basically +/- 90°, but with a cosine dependency according to lamberts law. Lateral light has only a small contribution to total measurement signal, but it's present anyway. So without an aperture that reduces the sensor's angle of view, above condition 2 also isn't true.
 

tsc230 +datasheet

FvM said:
If you take it away, it sees a bigger square, so the light (i'm not sure if this is the correct word) is increased.
Click to expand...
Completely wrong, unfortunately. You may want to consult an optics text book to understand why.

I think, it's like this:
1. If the paper would be illuminated evenly
2. If the sensor angle of view doesn't exceed the paper area
3. If the illumination isn't affected by the sensor's shade or reflected light
then the frequency wouldn't change

Point 2 may be ensured, point 1 and 3 never can in a real setup. If you think, you're able to, kindly explain how you did it.

If you intend to operate the TCS230 as a color sensor, the uneven illumination always present in a real enviroment isn't an issue, cause you can measure relative spectral intensities by utilizing it's different channels. There's a rich offer of TAOSINC application notes, that tell how to.

P.S.: An additional remark regarding angular sensitivity. As the datasheet reveals, TSC230 has a directional characteristic similar to any flat detector without optics, basically +/- 90°, but with a cosine dependency according to lamberts law. Lateral light has only a small contribution to total measurement signal, but it's present anyway. So without an aperture that reduces the sensor's angle of view, above condition 2 also isn't true.
Click to expand...

I agree with you in all the points, because i don't know too much about optic, but, how can you explain the behavior of the sensor in the experiment of the first post?

I mean, if the frecuency is increased, the total light that reaches the sensor must increase somehow. Maybe the sensor is receiving direct light from a lamp? or maybe light reflected? and what happens in the reverse direction? Why the frecuency drops, when the sensor is placed near the paper?

My appologies to thavamaran, my mistake. :oops:

Regards, Diego.
 

distance and color of light

Cause I don't know the illumination setup, I can only guess. Most likely the sensor is shading the paper. Or the mid area of the paper is less illuminated than one border, that comes into view range when increasing the distance. Generally an area appearing evenly illuminated to the human eye isn't in most cases, as a measurement reveals.
 

color intensity vs distance

Hey diegobob, No prob dude, u somehow tried to help me and i appreciate it. thank you man.

FvM, you are simply superb, thanks for guiding me through, the problem is frankly speaking i dont really understand your facts, i mean the spectral intensities which you meant, what is actually angular sensitivity, and what u mean by directional characteristics and cosine dependency.
 

color sensor distance

i dont really understand your facts
Click to expand...
Sorry for that. Angular sensitivity and directional characteristics e.g. are other words for what Figure 3 in TSC230 datasheet shows (they talk of angular displacement), it's a cosine function, as you can see. The same is discussed as Lamberts law in any optics text book.
 

sensor de color tsc230

Hey FVM, i will go through it first, thanks a lot for your guidance, do you mind if i pm you if i find any prob?
 

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