M, N

The maintained illuminance Ē_m is the (local) average of the installation below which the average illuminance must not fall at any time. The illuminance values defined for various occupations in the European standards such as EN 12464-1 are maintained values. If they are reached during the operation period due to lamp and luminaire degradation and dust, the installation must be maintained, i.e. cleaned, and the lamps must be replaced where necessary.

Unit: lux (lx)

The maintained luminance L_m is the (local) average of the installation below which the average illuminance must not fall at any time. Theluminance values defined for various occupations in the European standards such as EN 12464-1 are maintained values. If they are reached during the operation period due to lamp and luminaire degradation and dust, the installation must be maintained, i.e. cleaned, and the lamps must be replaced where necessary.

Unit: cd/m²

(MF) The maintenance factor accounts for lamp (or integral light source) and luminaire deterioration and soiling as well as soiling of reflection surfaces during the operation period of the lighting installation. It determines the initial value of illuminance/luminance and consequently the number of lamps and luminaires required. It can be defined as a reference maintenance factor based on standardised operating conditions or based on particular parameters of lamps and luminaires according to the lighting installation in question. Definition according to EN 12665: The maintenance factor is the ratio of average illuminance on the working plane produced by the lighting installation after a certain period to the average illuminance produced by a new installation under the same conditions.

The average vertical illuminance E_v on a cylinder surface yields the cylindrical illuminance E_z. The relation between cylindrical and horizontal illuminance E_h  defines the shadow detail E_z/E_h at this point. The shadow detail determines the perceptibility of three-dimensional objects and is also called modelling. In indoor spaces, its value at 1.2 m above the floor should be between 0.3 and 0.6.

see Regulation