Well, actually I didn't mean anything that fancy. I just meant a 1/2" diameter glass beaker with various percentage'mixtures of some powder that blocks light so you can vary the light intensity by varying the mixture percentage.I'm not a chemist or artist so I wouldn't have a clue what powder particles would work best. It only needs to be 1" high so size is not an issue. Most of the work would be experimenting to find a suitable powder.
Ok, but why? what does the result of this subtraction mean?
When the LED is ON the output is about 1000 and when it is OFF the output is about 30.I noticed that if I cover the phototransitor with my hand while the LED is OFF the readings decrease more, to about 3 a few times even 0.
You NEED to exclude outside light from your system. Thats why your "dark" reading is high as compared to this