On 27/05/2021 15:47, T i m wrote:
I have added an ambient light level sensor to my Home Assistant setup
and it seems to work very well (snapshot taken just now).

https://ibb.co/QHfKhv9

I've currently got it on an internal South facing windowsill so it
will already be looking though the double glazing [1] but I want to
print a case for it with it's own 'window' to keep the dust out I just
tried putting some plastic cut from a blister pack over it to see if
it would have any impact to the reading. It did, it went from about
11,000 lux to about 9,000 so I'm guessing it's only 'translucent' and
whilst I'm really only interested in the change of lighting levels
(for general lighting automation) I'd rather any such window didn't
impact the reading more than necessary.

The actual sensor is a TSL2561:
https://cdn-shop.adafruit.com/datasheets/TSL2561.pdf

And it suggests it combines the output of two sensors ...

"Each device combines one broadband photodiode (visible plus
infrared) and one infrared-responding photodiode on a single CMOS
integrated circuit capable of providing a near-photopic response
over an effective 20-bit dynamic range (16-bit resolution)."

So I was wondering if anyone could recommend a source of a small piece
of something as a 'window' that would be transparent for this role?

I have not read the spec on the sensor, but normal glass is opaque to
some wavelengths of IR, so that may account for the reduction in level.

(for thermal imaging cameras they often have to use lenses machined from
germanium).


--
Cheers,

John.

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