Illumination 29.02.2020 16:49 04.03.2020 18:50

The intensity of lighting (also illuminance in accordance with ČSN EN 12665) is a photometric value defined as the luminous flux incident on a particular surface. It is the quotient of the luminous flux (in lumens) and the area (in square meters). It is denoted as E. Its unit is a lux (lx), which is illumination caused by luminous flux 1lm incident on an area of 1 m².


A normal value of indoor light ranges from 100 ÷ 2,000 lx, on a sunny summer day outdoors it can reach up to 70,000 lx (at the latitude of the Czech Republic).
A clear moonlit night with the full moon represents the illumination of up to 0.5 lx.

Human sight is so adaptable that a person is able to read a clear text at approx. 10-8 lx.


Requirements for artificial lighting

Illuminance [lx]

The place and the activity


Communication in a flat


Living kitchens, bathrooms, toilets


Halls, reading in bed

50 ÷ 100

Total or graded illumination of the living room with local lighting

200 ÷ 500

Total or graded illumination of work areas without local lighting

200 ÷ 300

A common meal


Studying, writing, drawing, kitchen work, etc.


Delicate manual work, homework, blackboard in the classroom, office



The recommended ranges of illumination defined by the International Commission on Illumination (CIE):

Illuminance [lx]


20 ÷ 50

Basic orientation in the environment

50 ÷ 100

Simple orientation, short simple activities

100 ÷ 200

Social spaces, short-term work

200 ÷ 500

Routine work-related tasks (offices, schools)


The main requirements and criteria for the lighting of the interior of flats are: good orientation in space, visual comfort and colour rendering fidelity. This is what the parameters of lighting intensity are based on, as well as the type of lighting fixtures (incandescent bulbs, fluorescent lamps, discharge lamps, LEDs). The recommended maximum ratio of illuminance of adjacent spaces in the flat is 1:5.


The level of outdoor lighting and indoor illumination is measured by the C-RI-0401S module, or its variants, e.g. the C-RI-0401R-design, or the C-RI-0401I.