What would the possibility be of someone assembling and selling the sensor units which then could be attached to our own lux meter? Like most people I believe on this one, I would find acquiring the parts and putting everything together a little overwhelming. Yet making 10 would be litter harder than making one.
My guess they would sell like hotcakes at the right price. Sign me up.
Theoretically you could make just the sensors and let people splice them to their luxmeters. The problem with that is the difficulty in making all of the sensors exactly alike. That takes more accuracy in the dimensions than can be achieved with this design. Also, there is no guarantee that the several versions of that lux meter would all read the same with the same replacement sensor. DIY PAR Meter
is one approach that would stand a much better chance of being a true standardized sensor. If I could teach myself to do CAD drawings I would play around with this idea. I once knew how to use the very sophisticated CAD system Boeing uses for their commercial jet airplane design, but I have forgotten about all I learned about it.