[ QUOTE ]
Solomon said:
Could someone please give me an explanation about...
Lux?
Lumens?
Candlepower?
...and how they are measured? For example, does a 500 lumen flashlight equate to 500,000 candlepower?
Thanks in advance!
[/ QUOTE ]
This is complicated and confusing. Here is the fairly rigid explanation. Candlepower is a measure of luminous intensity when specifically measured in units of candelas. This is like "mileage" is a measure of distance when the unit of measure is in miles. Luminous intensity is a measure of light [flux] passing through a unit of *solid angle*. A candela is the intensity produced where there is one lumen [flux]per steradian [the measure of solid angle]. Lux is a unit of measure of illumination which is a measure of light [flux] *falling on a flat area*. One lux is the illumination produced when there is one lumen [flux] falling on a square meter. Lumens are a measure of total light [flux]. Think of a focusable flashlight. As the beam is adjusted from broad to narrow, the total flux [lumens] stays the same but the illumination of a surface or intensity [lux or candelas] within the beam increases. Illumination [Lux] or candlepower [candelas]can be measured with relatively simple instruments. Flux [lumens] is much more complicated. Most commonly an integrating sphere is used to capture all of the light emitted by a source and then the illumination is measured at a fixed point in the sphere. Through complicated calibrations this illumination measurement is then correlated with a flux value.
Some folks incorrectly think that candelas [candlepower] and lux are units of measure of the same thing but this is not quite correct. It is true that a point source with an *intensity* of one candela will produce an *illumination* of one lux at a distance of 1 meter but this does not make them measures of the same thing.
>For example, does a 500 lumen flashlight equate to 500,000 candlepower?<
No. They are measures of different things.