Illuminance (usually 'E' in formulas) is the total luminous flux incident on a surface, per unit area.This word has been proposed by the Colorimetry Committee of the Optical Society of America to replace the term illumination.
In SI Iiluminace is measured in lux (lx) or lumens per square metre (cd·sr·m-2). In the CGS system, the unit of illuminance is the phot. One phot is equal to 10000 lux.Illuminance is defined:
Illuminance Ev = Luminous intensity Iv /radius
Illuminance is a very important factor when we talking about the quality of light in a working environment or at home. The table below shows some examples from the CIE Code for Interior Lighting :
| Category | illuminance [lux] | Example | ||
|---|---|---|---|---|
| General areas that are not in permanent use or that do not demand a high visibility of the task | 20 |
30 |
50 |
public areas |
50 |
100 |
150 |
orientation during short stop |
|
100 |
150 |
200 |
rooms that are not in permanent use |
|
| General lighting for indoor work | 200 |
300 |
500 |
details easy to see |
300 |
500 |
750 |
(offices) |
|
500 |
750 |
1000 |
quality control |
|
| Tasklighting for highly demanding work | 750 |
1000 |
1500 |
demanding task undertaken for an extended time |
1000 |
1500 |
2000 |
extremely fine details |
|
>2000 |
special tasks (surgery) |
|||
| Recomended for reading | 300
| |||
Illuminace is measured with a photometer.Most photometers are based on a photoresistor or photodiode.
In general, photometers may be divided into two classifications: laboratory photometers, which are usually fixed in position and yield results of high accuracy; and portable photometers, which are used in the field or outside the laboratory and yield results of lower accuracy.