What is meant by Candela/m2?

[sarith]

@MaxMarschall

It is getting clearer for me now, though I’m still having trouble with the “/m2”. You mentioned the “impact of light at a point”, and the “illuminance produced at the measurement point” - where do the m2 come into play, if we’re talking about a measurement point receiving light from another point?

Both luminance and illuminance are measured for infinitesimal areas (as per definition). So, the m2 comes from there. For empirical measurements, this area is the area of the transducer(sensing element) in the illuminance or luminance meter. I would suggest referring the 10th Edition of the IES Lighting Handbook for an exact definition and derivation. Actually, wikipedia does a decent job of explaining the definition too.

@MaxMarschall

Let me ask it this way: is the following diagram accurate?

Conceptually, yes. They do convey that illuminance is a quantity measured on a surface and luminance is quantity measured in a specific direction based on the observer/measuring device. However, besides the Photopic efficiency curve/luminous efficiency function, the empirical measurement of luminance and illuminance have nothing to do with the eye. Both these quantities are calculated by weighting the electromagnetic radiation in the visible spectrum with the V(λ) function.

@LiamRuvio

Dear @sarith, are you aware if there are any standards/code, with minimum or maximum requirements not to reach and/or exceed, according with the type of use, for example psychological or physiological glare?

It’s been a while since I looked up any of the standards, but metrics like UGR, DGP etc. all account for luminance, contrast and source size. The dissertation work by Kevin Wymelenberg and the related papers published by him contain a thorough discussion on this topic.

Regards,
Sarith