# Thread: Candle power to lumens?

1. ## Candle power to lumens?

Are they convertible?

2. The technical answer is yes - you need convert candlepower to candela (1 candlepower = 0.981 candela. Next you need to know the radiation angle in degrees, then the formula is

luminous flux (lumens) = luminous intensity (in candelas) 2π (1 - cos(A/2)), where A is the radiation angle in degrees.

So in short, while it is technically possible, in practice no-one does.

The reason for the complexity is that candlepower and lumens are measuring 2 different but related things. The way I get my head around it is to think of 2 identical LEDS, at the same current & temperature these identical LEDs will emit the same amount of light measured in lumens.

If you focus one LED through a 30 degrees and the other through a 10 degree lens. Your eyes will tell you that the 10 degree lens is brighter, but has a narrower beam. The amount of light (lumens) stays identical but the candlepower measurement of the 10 degree lens will be much higher, matching what you saw with your eyes.

Or if you prefer even less technical, take two cans of beer. Pour one into a short, wide glass, the other into a tall skinny glass. Lumens is a measurement of the total volume of beer, candlepower is a measurement of the depth.

Now drink the two beers

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