On Thu, 27 May 2021 20:26:49 +0100, Jeff Layman
wrote:

snip

Thanks for all the suggestions so far guys. A few things to try there.

Have you considered an old camera lens glass for the cover?

No, I hadn't (so thanks). I had thought of similar in the form of a
microscope slide but I can remember buying 'daylight filters' for my
SLR cameras to (sacrificially) protect the lens from physical damage.

If you don't
have one, a camera shop selling secondhand film cameras might have some
old partially-broken lenses which could serve as a source, or even an
old UV filter.

Our last camera shop went a few years ago but we do have a 'Cash
Converters' that may have a bits n bobs bin.

However, depending on what spectral range you are trying
to measure the light level of,

According to the spec I believe it covers the range of 300-1000 nm
(even though I understand we can only see around 380 to 750 nm etc)
but what I would describe as 'daylight' is all I'm really interested
in re managing general light levels indoors. Given this sensor seems
to be designed to 'see' the sort of thing we see, I think that as long
as whatever light it gets isn't filtered at all, it should be ok.

you might want to have a look at this first:
https://petapixel.com/2020/06/04/why-uv-filters-are-basically-useless-on-modern-cameras/

Interesting.

Whilst I had a few film cameras along the way I never really used them
much because of the time delay between taking the / 'a' picture and
getting the result. Ignoring my time with Kodak (microfilm / fiche)
and the Polaroid and a scanner on my PC, my first digital (A Fuji
DX-5) revolutionised it all for me and the fact that it was only
640x480 didn't matter for my needs, 'instant reference photographs'
(engineering stuff).

I hadn't thought of a round 'window' but one makes sense and one I
could easily incorporate in a 3D printed box.

I'm not trying to actually 'measure' anything (although the sorts of
levels are interesting if they are correct and when compared with the
stated light output levels of domestic lighting) but to just get the
comparable levels that could be useful to automate what might equal
'it's a bit dark outside, better turn the light on', or enable the
'turning on a light on in the hall automatically with a PIR during an
overcast day and before sunset' ... sort of thing. ;-)

Cheers, T i m