Lumen, Lux and Candela
Question to Knivesandtools:
You often see the terms Lux, Candela and Lumen in the features of torches. What do they mean and are they connected?
Answer of Knivesandtools:
Lumen, Candela and Lux are 3 measures for measuring light. They cannot be compared directly however.
Lumen is a measure for the total quantity of light radiating from a lamp. Indications in lumen do not take into account how the light is bundled. Two torches that supply the same number of lumen are not necessarily as bright as each other, or shine as far.
Lumen is a measure currently used a lot in the specifications of torches. However the number of Lumen does not say anything about how far a light shines. You then at least have to involve the shape of the bundle at least.
Fortunately many manufacturers now also indicate how far a torch shines, in addition to the number of Lumen, and we have also measured ourselves. Read more here: Overview strongest torches
Lux is a measure for the strength of the light falling in a specific place. For example on a wall or the floor of an office. 1 Lux is approximately the strength of light of a candle at 1 metre's distance.
You can add up Lux, i.e. if 1 candle produces 1 Lux at 1 metre's distance, 2 candles give 2 Lux light at 1 metre's distance.
If the distance of a light source doubles, the number of lux on a surface is 4x smaller. I.e. an average candle produces approx. 0.25 lux at 2 metres' distance. This is because the surface to be lit is then 4x larger.
Lux is not a unit that can be used to express the light strength of a light source like a torch. However it is a unit on which the units candela and lumen, which are used in the specifications of torches, are based.
Candela / Candle Power
Candela, or Candle Power is the number of lux that a light source produces at 1 metre's distance, in the brightest spot of the light bundle. It is a measure that was often used in the past for specifying the light strength of torches. Candela says something about the light strength but not about the total quantity of light. With a reflector or lens you can bundle the light to obtain more light strength (and therefore more Lux) without having to use a more powerful lamp.