There are some seriously sophisticated (and inexpensive) light sensors available these days. I wanted to see how they'd work outdoors so I designed a weatherproof enclosure for them to augment my weather station data.
I wasn't quite sure if this would work so I thought I'd wait a little while before sharing because honestly, I didn't think it'd last a month. That was back in 2016. After multiple blizzards, hurricanes and extended heat waves it's still going so I figure it's ok to post the design at this point.
Enclosure Design and Construction
Instead of 3D printing the whole thing I used a piece of 4" PVC for the main body which is cheaper, faster and stronger.
The dome is an acrylic replacement security camera dome I found on Amazon for a couple bucks. The exact one I used isn't available anymore but anything close should work fine. In case yours is a little different I included STEP files so you can make modifications. I used some small screws and pipe thread compound (TFE paste) as a gasket to waterproof the dome.
Mount it to your mast with a U bolt.
Sensor Suite Design
Inside the enclosure is a Raspberry Pi with WiFi that pushes data from the I2C light sensors to an IoT Dashboard. It's all pretty straightforward stuff. If you want to recreate my build I've included a PDF of my design notes.
Acrylic is transparent to visible light but blocks certain other wavelengths so most, but not all of the sensors I used will work to their full potential. Quartz would be a better choice but, you can't find a dome in that material on Amazon for a couple bucks.
What you can find (not as cheap but still a reasonable price) is a 1/8 x 3-1/2 square ground and polished fused quartz plate. That'd be the ticket to taking this idea to the next level.