Hey builder(and whoever else), I have a quick question for ya: are lux and candelas/lumen different?
YES
I need some good solid information to research about that but I just can't seem to find it haha, thanks!
The
lux (symbol:
lx) is the
SI unit of
illuminance and
luminous emittance. It is used in
photometry as a measure of the intensity, as perceived by the human eye, of
light that hits or passes through a surface. It is analogous to the
radiometric unit watts per square metre, but with the power at each
wavelength weighted according to the
luminosity function, a standardized model of human visual brightness perception.
Explanation
Illuminance is a measure of how much
luminous flux is spread over a given area. One can think of luminous flux as a measure of the total "amount" of visible light present, and the illuminance is a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area.
In SI, luminous flux is measured in
lumens. One lux is equal to one lumen per square metre:
Lux versus lumen
The difference between the lux and the
lumen is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. However, the same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single
fluorescent light fixture with an output of 12,000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
Lux versus footcandle
One
footcandle ≈ 10.764 lux. The footcandle (or lumen per square foot) is a non-
SI unit of illuminance. Like the
BTU, it is mainly only in common use in the United States, particularly in construction-related engineering and in building codes. Because lux and footcandles are different units of the same quantity, it is perfectly valid to convert footcandles to lux and vice versa.
The name "footcandle" conveys "the illuminance cast on a surface by a one-candela source one foot away." As natural as this sounds, this style of name is now frowned upon, because the dimensional formula for the unit is not foot · candela, but lumen/sq ft. Some sources do however note that the "lux" can be thought of as a "metre-candle" (i.e. the illuminance cast on a surface by a one-candela source one metre away). A source that is farther away provides less illumination than one that is close, so one lux is less illuminance than one footcandle. Since illuminance follows the inverse-square law, and since one foot = 0.3048 m, one lux = 0.30482 footcandle ≈ 1/10.764 footcandle.
In practical applications, as when measuring room illumination, it is very difficult to measure illuminance more accurately than ±10%, and for many purposes it is quite sufficient to think of one footcandle as about ten lux.
What it all boils down to is LUX is a measurement of all visable light, usable and unusable.
By the way the quantum meter should be here soon.
