Radiometer/Light Meter


I am trying to create a digitally controlled garden. My first step in this project is to create a Radiometer to measure the available light in the garden. I am planning on taking hourly readings from at least one sensor and push that to a database to monitor changes over the season.

I want the sensor to be accurate; I have been researching different types of light meters. I have read that to be accurate I should use a solar cell not a photo-resister and measure the current from the solar cell not the voltage.

If I hook up the solar cell to a small fan, what is the easiest way to measure the current in that circuit as something I can read on an Arduino pin?

Any help would be very much appreciated :)


You can “meassure” 2 things with Arduino, either digital 0 (=0V) or 1 (=5V) on the digital pins, or 0 - 5V on the analog pins, Arduino vil convert this voltage to a number in the range 0 - 1023.

So your best bet is to find a way to convert current to voltage. some info here

Another option would be to find a light sensor that can communicate using serial communication.

These people have many solutions for you:

Those Light-To-Voltage devices look like just what I need. Now I just need to figure out how to display the input as "Foot Candles" :o


Well 1 watt/cm2 is 634528 foot candles at 555nm wavelength.

Where in the world did you find that? Is there a table or something?


I did a Yahoo search but unfortunately, I didn't bookmark the site.

Just to add back to the group, I think this is the site JaguarJoe used. I think accuratly measuring solar radiation is going to be difficult, but I am not giving up yet.