Uniformity U0 is defined as the quotient Ēmin/Ē of minimum and average illuminance in the visual task area, keeping in mind that this minimum value must not be undercut at any time. Where the decrease in minimum illuminance due to degradation or premature failure of individual lamps progresses more rapidly than the decrease in average illuminance, maintenance or cleaning of the installation must be effected as soon as minimum uniformity is reached. The uniformity of illuminance U0 for the immediate surrounding area should be at minimum 0,40. The determination of uniformity requires a sufficiently close sequence of calculated or measured localised illuminance values to be able to determine minimum illuminance. For details, see chapter "Lighting measurement".
