Reflective photoelectric sensor design issues

[Murugesh_89]

Hi,
I am designing photoelectric electric sensor of reflective type. I am detecting the objects of various colors.

When i place some objects of light colors like sky blue,grey... the detection is working. But when i place dark objects like red,black,green... the sensing is not happening for even a distance of about 10mm. I think these dark objects absorbs the light source and not reflect it back.

I am using a IR photo emitter with wavelength of 950nm by passing a current of 135mA (forward current of 150mA has given in datasheet).

What should i do to overcome this issue to detect dark color objects too..

Thanks,
Murugesh

 

[chuckey]

First of all make sure your light emitter is actually emitting light at these wavelengths, if not use a wideband source (light bulb!!). If the objects are not reflecting any light, you tell me how you are going to detect it!
Frank

 

[Murugesh_89]

Thanks for your reply.

Light color objects are reflecting the light. Dark color objects only not reflecting.
So what wavelength should i use to detect both light and dark color object.

 

[chuckey]

"o detect both light and dark color object." The lightness or darkness of a colour is its luminance. The wavelength of the reflected light is its colour. You can have a piece of black velvet with a spot of red on it, it reflects very little light but what light it reflects will be red. if you shine a green light onto the cloth it will not reflect anything at all. if you shine a red light on it it will reflect a little red light.
Frank