The maintained illuminance Ēm 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)