I'm currently trying to measure the light intensity of a LED that flashes rapidly (my flash lasts 200ms). I was initially planning to use a photoresistance (a classic light sensors, like the Adafruit VEML7700) but I don't think its response time is good enough. I need to be able to measure the maximum of the light intensity during this brief flash. Could a photodiode or a phototransistor be the solution? I'm using the Arduino Nano card. The light intensity expected should be around 6000lux.
A phototransistor is easier to use than a photodiode. It doesn't need as much gain and it doesn't need a transconductance amplifier. You might not even need an amplifier, but I don't have a feel for that...
You'll need a known-good light meter. Obviously it doesn't need to be as fast.
Not that with the Arduino you only "sample" the analog input for an instant every time it's read (usually in a loop). But 200ms should be long-enough as long as the loop isn't doing too much "extra".
There is an op-amp circuit called a peak detector that can "hold" the peak analog voltage for a period of time. (I use peak detectors for audio.)
I built and tested this circuit so I know it works.
Photodiodes produce a leakage current that is directly proportional to
the intensity of the light. The output current vs. incident light can be
linear over 6-9 orders of magnitude.
I do have a light meter but its sample rate is 2,5 time/sec which is not so good, but that could do I think. Though the precision of my measurements won't be so great in the end, which is why I was hoping I could use a calibrated light sensor directly (VEML7700). But thank you for your help!
Obviously it doesn't need to be as fast.