- For other meanings, see Lux (disambiguation).
The lux (symbol: lx) is the SI unit of illuminance. It is used in photometry as a measure of the perceived intensity of light. In English, "lux" is used in both singular and plural[1].
Definition
1 lx = 1 lm/m2 = 1 m2·m–4·cd
SI multiples
| Multiple |
Name |
Symbol |
|
Multiple |
Name |
Symbol |
| 100 |
lux |
lx |
|
|
|
|
| 101 |
decalux |
dalx |
|
10–1 |
decilux |
dlx |
| 102 |
hectolux |
hlx |
|
10–2 |
centilux |
clx |
| 103 |
kilolux |
klx |
|
10–3 |
millilux |
mlx |
| 106 |
megalux |
Mlx |
|
10–6 |
microlux |
µlx |
| 109 |
gigalux |
Glx |
|
10–9 |
nanolux |
nlx |
| 1012 |
teralux |
Tlx |
|
10–12 |
picolux |
plx |
| 1015 |
petalux |
Plx |
|
10–15 |
femtolux |
flx |
| 1018 |
exalux |
Elx |
|
10–18 |
attolux |
alx |
| 1021 |
zettalux |
Zlx |
|
10–21 |
zeptolux |
zlx |
| 1024 |
yottalux |
Ylx |
|
10–24 |
yoctolux |
ylx |
Explanation
One lux is equal to one lumen per square metre.
| Illuminance |
Abbr. |
Example |
| 0.00005 lux |
50 µlx |
Starlight |
| 1 lux |
|
Moonlight |
| 400 lux |
|
A brightly lit office |
| 400 lux |
|
Sunrise or sunset on a clear day. |
| 1000 lux |
1 klx |
Typical TV studio lighting |
| 1000 lux |
1 klx |
Approximate minimum level required to reset the biological clock in humans |
| 32000 lux |
32 klx |
Sunlight on an average day (min.) |
| 100000 lux |
100 klx |
Sunlight on an average day (max.) |
Trivia: Unicode has a symbol for "lx": (㏓), but this is just a legacy code to accommodate old code pages in certain Asian languages, and it is not recommended for use in any language today.
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. 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 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 12000 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 with the same number of lux requires a larger number of lumens.
Relationship between illuminance and power
Illuminance is not a direct measure of the energy of light, but rather of the illumination it provides as perceived by the human eye. Thus, the conversion factor varies with the wavelength composition or color temperature of light. At 555 nm, the middle of the visible spectrum, one lux is equal to 1.46 mW/m².
SI photometry units
Non-SI units of illuminance
