Light Sensors

Your question doesn't make sense. Please explain more.

I don't think you'll find any photodiode that will do this without some clever electronics. The big problem is that you could easily have 3 or more orders of magnitude difference between the output in sunlight and streetlight - that's a factor of at least 1000.

What I think you'd need would be a logarithmic amplifier, which would give you, say, 4V output in sunlight and 1V output in streetlight. You'd then need to detect the change in output as a car passes - say from 5V to 4V in full sunlight and 2V to 1V under streetlight. You'd need to calculate a rolling average of the output level as it slowly changes from mid-day through afternoon and evening to night, and your system would need to be triggered only by the rapid changes as a vehicle passes over.

An interesting project. I'm sure what you want to do is possible, using e.g. a silicon PIN photodiode & appropriate electronics, but I'm afraid you have a lot of work ahead!

Good luck,

John

As John says, log amp is the way to go for sure if you want to use the same diode.

I have some links to useful information on my other computer that has simple trigger circuits used for lighting, car light etc. detection. A web search would be fruitful too. The circuits are hooked up to a camera, but that load could change to anything limited by your imagination.

From a photographic point of view, using the same diode receptor for both sunlight and street light will require at least 16 stops (like the "order of magnitude") and a crazy "factor" many more times than 1000.

Best to use two diodes and equilavent circuit for each, one for sun light and the other for street light etc..

...and it is my view that any quality light diode receptor will do. It will be the circuit that determines your end result.

AFAIK, f stops are arranged in a sequence of factors of 2, e.g. f/2 lets through half as much light as f/1. So 16 stops would be 65536, which is between 4 & 5 orders of magnitude.

I agree that one decent photodiode would cover the range - one of our products is an optical densitometer which measures density up to 5 (that's 100,000 to 1 in terms of transmitted light) - using a PIN diode with an autoranging amp/ADC. A previous model did the same job using a (now obsolete) log amp IC.

crikies, gonna have to think on this one after a coffee