I'm not familiar with the studio formula lighting idea. By that is it meant that the ratio of light intensities is specific instead of eyeballed?

How does falloff distance come into play with the formula lighting idea?

And did you mean (main=1,fill=2,ambient=4)? That seems odd.

The meter measures illumination from light sources. Unless you enable IDL, the amount of light or luminance from an object in the scene is not included in that measurement.

Real light meters when held close to an object measure the perceived luminance of that object. If the object is dark, this can be very low even in the presence of strong lighting. If the object is white (like snow), it can be very high even in the presence of weak lighting.

The light meter measures the lighting intensity (illumination), not the object luminance (reflected light). 

It would be possible to measure the object luminance, but only if IDL is enabled and you point the meter at the object and swing your camera around so you can see the meter.

Having said that, the meter could be modified to measure and report luminance using the zone system, although that would get into an interesting problem of visual representation. Ideally, the meter would display a zone number. It would be possible to do so with a suitably arranged image with the roman numerals on it. Also the shape of the meter should be flat and use a Clay node as the sensor, instead of a Diffuse node, so that it can more consistently measure the luminance independant of angle of incidence.

 

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)