How do I convert between candelas and lumens?

You can’t directly convert since they measure different things. The most useful explanation I’ve found is that lumens measure light output at the source, while candelas measure the light that falls on a surface. As the area of the surface increases, the number of candelas will decrease even as the number of lumens remains constant. So, they measure different things, and there’s no direct conversion. Update: I didn’t find that answer very satisfying either, so I worked out the conversion details and made a conversion calculator for you to use.

Light bulbs and LEDs sold for illumination tend to carry ratings in lumens. Indicator LEDs tend to be rated in candelas.

You can also use this table to get an approximate conversion from candelas to lumens. Find your LED beam width in degrees, and divide the candelas number in your specs by the cd/lm factor listed for that beam angle to get lumens.

beam angle	cd/lm
5		167.22
10		41.82
15		18.60
20		10.48
25		6.71
30		4.67
35		3.44
40		2.64
45		2.09

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