First let us know more about illumination
Illuminance means the illuminated object’s luminance fluxes per unit area. (lm/㎡), the unit is Lux. It can be measured by illuminometer/luxmeter and can be classified as horizontal illuminance and vertical illuminance.
1Lux means the brightness that 1 lm averagely distribution in 1 square metre place. (1 Lux = 1 lm/m2).
And there is another unit of illuminance which is foot-candle. It conveys “the illuminance cast on a surface by a one-candela source one foot away”, the abbreviation is 1ftc (1lm/ft2) that is the illuminance when the luminance flux is 1lm per square foot. And 1ftc=10.76lux.
In order to have more perceptual understanding to illuminance, take an example to calculate it as follow:
A 100w incandescent bulb will give out the whole luminance fluxes of 1521lm, if those luminance fluxes uniformly distribute on a hemisphere, if we do not consider the reflection of light on the surface of hemisphere, then we can calculate the illuminance of 1m away from light source( the 100w incandescent bulb) and the illuminance of 5m away from light source as follow:
The hemisphere’s radius is 1m, so the area of it is 2π*12=6.28 m², the illuminance of 1m away from light source is 1521lm/6.28m²=242.2Lux.
In the same way, The hemisphere’s radius is 5m, so the area of it is 2π*52=157m², the illuminance of 5m away from light source is 1521lm/157m²=9.7Lux.
The application of illuminance and the reference standard of lighting design
Illuminance can show the received luminance flux in the surface of some objects. Because the illuminance can directly show the brightness of object’s surface, so all country are set up the lighting design standards according to the illuminance.
Here I will introduce some illuminance standards for home use in some countries, the unit is Lux. You can refer to this in the daily life, and based on the different situations, illuminance is flexible.
Find it helpful and interesting? Recommend this blog to your friends. Let us learn more everyday together.