I have two sealing needs. One is around the joint between the cap and the box, or jar, both of which are acrylic plastic. The other is around the guts of the lux meter to hold it in place, and also to seal the pass thru hole for the electric cable. I was considering silicone for the second , and acrylic cement for the first (not methacrylic super glue).
My present plan is to leave the lid off the box until the silicone cures around the luxmeter guts, which would also reduce the volume of air in the box, but not in contact with any of the electric elements. Also a fillet of silicone outside around the electric cable. After the silicone cures, probably 2 days later, screw on the lid and apply high viscosity acrylic cement around the joint to seal it permanently. Would that adequately protect the diode, etc. from any fumes? And, do you think the limited adhesion of silicone to acrylic would be enough to seal up the electric cable hole - the cable fits pretty tight in the hole, so it is just the tiny surrounding gap the would be sealed.
Before I consider playing around with optical filters or other methods for changing the response of the diode, I want to try this as is, relying on calibrations using a PAR meter, for each type of lighting I will use it for. If that doesn't work well enough, then I can buy another lux meter and play with it further.