lux and light intensity for pharmaceutical
The lux (symbol: lx) is the SI derived unit of illuminance, measuring luminous flux per unit area.[1][2] It is equal to one lumen per square metre. In photometry, this is used 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 watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used as both the singular and plural form
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total "amount" of visible light present, and the illuminance as 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 when the luminous flux is held constant.
One lux is equal to one lumen per square metre:
A flux of 1000 lumens, concentrated into an area of 1 square metre, lights up that square metre with an illuminance of 1000 lux. However, the same 1000 lumens, spread out over 10 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 to the same level of lux requires a greater number of lumens.
As with other SI units, SI prefixes can be used, for example a kilolux (klx) is 1000 lux.
Here are some examples of the illuminance provided under various conditions:
| Illuminance (lux) | Surfaces illuminated by |
|---|---|
| 0.0001 | Moonless, overcast night sky (starlight)[4] |
| 0.002 | Moonless clear night sky with airglow[4] |
| 0.05–0.3 | Full moon on a clear night[5] |
| 3.4 | Dark limit of civil twilight under a clear sky[6] |
| 20–50 | Public areas with dark surroundings[7] |
| 50 | Family living room lights (Australia, 1998)[8] |
| 80 | Office building hallway/toilet lighting[9][10] |
| 100 | Very dark overcast day[4] |
| 150 | Train station platforms[11] |
| 320–500 | Office lighting[8][12][13][14] |
| 400 | Sunrise or sunset on a clear day. |
| 1000 | Overcast day;[4] typical TV studio lighting |
| 10,000–25,000 | Full daylight (not direct sun)[4] |
| 32,000–100,000 | Direct sunlight |
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