I found an acrylic round, screw-top box, 2.75 inches in diameter, which will work great as a housing for the sensor. It is available online, http://www.consumercrafts.com/store/...torage/1125-53
Unfortunately, only one lid comes for the 4 boxes, but it also only cost me $2.25 at Michaels. Here is what it looks like:
I will have to cut the sensor housing down in length but it is empty in that area anyway. Now, how to make the sensor watertight? I'm thinking I could essentially pot it with silicone, so the hole for the electric cable will also be sealed. The lid will have to be cemented on, either with silicone or with acrylic cement.
The acrylic lid attenuates the meter reading from 99 to 89 lux with it sitting on my desk and the overhead CFL light lighting the room. That would be a 10% loss due to the lid, which would just change the conversion factor from 60.6 to 67. Not a problem, that I can see.
There is a tiny "instruction manual" with the luxmeter, which has this chart on it:
Clearly this is not consistent with a true PAR meter, but calibration against a PAR meter for specific light sources should take care of this easily enough.