Here’s an example of how to use the table:
Page 89 of the widgetco catalog offers two white LEDs. The specs are listed as follows:
Ultra-bright white LED: 16,000mcd 5° beam angle
Mega-bright white LED: 9,000mcd 10° beam angle
You want to purchase the one that will give the most light flux in your solar accent light. Which one do you select?
Ultra-bright gives 16cd / 167 cd/lm = 0.10 lm
Mega-bright gives 9cd / 42 cd/lm = 0.22 lm
Wow, Mega-bright throws over twice the flux as Ultra-bright. Would you have guessed from the catalog listing?
The caveat is that you have no idea from the specs listed what angle the maker used to measure the intensity (millicandelas). Theis exercise assumed that it was measured over the entire beam angle. That’s reasonable–you would expect the manufacturer to publish the highest possible intensity spec. But there’s a couple sources of error in this approximation: first, there’s light outside the beam half-power angle, and second, the light inside the beam half-power angle isn’t guaranteed uniform by any means. So we’ll call this an approximate conversion. Your mileage may vary.
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