For an outdoor system I'm designing, I'm looking for a sensor able to detect a signal light from a distance of 50-150 metres and provide an output to a low-end microcontroller (i.e. not enough processing power to deploy CV). Cost might be high if reliability also is. Key features of the setup are:
-the signal light is diffused inside a cube whose side is approx. 12-15cm long. I will measure light intensity on a side of that cube;
-the diffused light is not significantly stronger than ambient daylight and the system will operate during the day;
-the light is colored and I can choose the color as long as it's in the visible spectrum;
-the light works in an on-off fashion and I have all the time in the world to determine any threshold values if the system needs them;
-response times of 0,1s or less are acceptable;
-it's ok if the sensor will have to be stationary.
A ready-made sensor is a luxury I can ditch easily - I investigated collimators and other optical components and I think I could devise a custom solution myself, but my knowledge of optics is limited. I think what I need might be compared to a single-pixel camera; if I'm correct, the sensor in a custom solution would probably be a simple photoelectric one, but the optics would be the most complex part, the one I need most pointers for.
My creative instincts seem to have died down when investigating this issue, so I'll be most grateful for any advice. Thanks!