"watt is a poor measurement for measuering the quantity of visible light"
Actually, it's a great measurement if you only work with the monochromatic ones. Knowing the LEDs efficiency at bin testing conditions will tell you what to expect - E.G. high-bin 3w 460n LED with 50% efficiency at 3w drive and typical operating temperatures (~70C junction temperature) means you can expect 1.5W of light. We toss in Avogadro's constant and a couple other formulas, do some multiplication, and suddenly we know roughly how many photons are being put out.
This gets harder with white LEDs as one must figure out the relative percentage of each wavelength comprising the light, basically forcing you to do the math a few hundred times over, but it's still rather reliable. I just do rough calculations in my head for White LEDs.
Actually, it's a great measurement if you only work with the monochromatic ones. Knowing the LEDs efficiency at bin testing conditions will tell you what to expect - E.G. high-bin 3w 460n LED with 50% efficiency at 3w drive and typical operating temperatures (~70C junction temperature) means you can expect 1.5W of light. We toss in Avogadro's constant and a couple other formulas, do some multiplication, and suddenly we know roughly how many photons are being put out.
This gets harder with white LEDs as one must figure out the relative percentage of each wavelength comprising the light, basically forcing you to do the math a few hundred times over, but it's still rather reliable. I just do rough calculations in my head for White LEDs.