Using long exposure to measure low luminance on a display

[spacediver]

thanks for the link, some of those instruments are wonderful

Yes, so quantum efficiency determines the proportion of photons that are converted into electrons by the sensor, and clearly, higher quantum efficiency means higher sensitivity to light.

But wouldn't a larger photosite (keeping fill factor constant) also mean that more photons are able to "innervate" each pixel? And don't larger sensors tend to have larger photosites?

Ideally, you'd want high quantum efficiency AND larger photosensitive regions per photosite... I wonder if the tradeoff is linear. So take two sensors:

A: CCD sensor with 80% quantum efficiency. Size = 400 square mm.

B: CCD sensor with 40% quantum efficiency. Size = 800 square mm.

I wonder if they'd be equally sensitive.

I do appreciate, however, that the fill factor of CCDs can be much larger than those in CMOS, so even though the CMOS sensors might be larger, the photosensitive regions in each photosite may be smaller.

 

[flood]

^should be equally sensitive. since we're averaging over all pixels, the size of each photosite doesn't matter, but the total size of the photo-sensitive regions would be the important thing.

yup without a doubt scientific/astro/non-general-purpose cameras would be better suited for this, but I'd also like to get something that is useful for other purposes. if the casio ex-zr700 is good enough, i'll just use it.

or.... are there any cheap (<$300) instruments specifically designed for measuring low luminances?

 

[spacediver]

^should be equally sensitive. since we're averaging over all pixels, the size of each photosite doesn't matter, but the total size of the photo-sensitive regions would be the important thing.

makes sense

or.... are there any cheap (<$300) instruments specifically designed for measuring low luminances?

The konica minolta LS-100 is used in many labs (including the lab I work in), and it can only read down to 0.001 nits (and it costs thousands of dollars used). The Klein K10-A can read extremely low, but again, thousands of dollars.

I wonder if a cheap sensitive lux meter could be used. I think (but not certain) that unlike a luminance meter, which has an aperture at a given solid angle, a lux meter measures illuminance over the hemispheric solid angle, so it should be more sensitive. And the scaling factor idea should work (you could probably directly infer luminance by measuring the distance of the lux meter from the screen).

My hunch is that long exposure with quality sensor is the best idea though.