Comparing two units of light output can be confusing when they are measured in differing units and have similarities yet are different. When it comes to quantities of light, you often see either lumens or candlepower.
The lumen (lm) is a unit of measurement for luminous flux, that is used to show how strong or intense a light source is. It measures the total quantity of visible light emitted from a light source regardless of its direction.
So lumens measure the amount of light that is produced by a light bulb, flashlight or lighting fixture. The more lumens, the brighter the light will be.
Candlepower (c) is the unit of measurement for luminous intensity. It measures the amount of light that is emitted in a particular direction, particularly the brightest central location of a focused beam.
Candlepower refers to the common and uniform output of light from when the candle was the main source of light.
Despite the term candlepower still being used today by flashlight and torch manufacturers today, it was officially changed to the term and unit of candela in 1948.
1 candlepower is equal to 1 candela.
1 candlepower is equal to the amount of light produced by 1 candle.
Lumens measure the total amount of light created by a source, whilst candlepower typically measures the amount of light in a focused beam.
For example, though lasers have a high candlepower because the light is concentrated into one point, it would have a low lumen value because it does not give off much light.
In terms of light bulbs and general lighting, you will always see the lumen measurement as this is the more accurate indication of how bright a light will be.
However, with flashlights, spotlights other focused beams of light, manufacturers may still use candlepower to show the strength of their product.
It’s important to check which unit of measurement is being used before you buy a flashlight as candlepower can be much higher than lumens, making it appear as though it will be brighter.
As lumens and candlepower measure two different things, converting between them isn’t wholey accurate but for estimation purposes there is an approximate relationship between the two:
1 candlepower = 12.57 lumens
1 lumen = 0.796 candlepower
Despite 1 candlepower being more lumens and looking brighter at it’s focused point, the intensity of that light and it’s perceived brightness is dependant upon the color temperature of that light.
The human eye will perceive a whiter color as brighter than a more yellow one. More specifically, a 5000K color of white light will feel brighter than 1500K, which is the color of candle light.
So the intensity of candlepower vs lumens is also dependant on the color temperature.
Candlepower is useful as a measurement as it describes the strength of light in a focused beam which can be useful for products such as torches, lasers and spotlights.
However, when it comes to general lighting around the home and for making general comparisons between light sources, lumens are always the best indication of how bright a light will be.
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