equivalent luminance (of a field of given size and shape, for a radiation of arbitrary relative spectral distribution) [Leq]

luminance of a comparison field in which radiation of frequency 540×1012 Hz has the same brightness as the field considered under the specified photometric conditions of measurement; the comparison field must have a specified size and shape which may be different from that of the field considered

Unit: cd·m-2

NOTE 1 Radiation at a frequency of 540×1012 Hz has a wavelength in standard air of 555,016 nm.

NOTE 2 A comparison field may also be used in which the radiation has any relative spectral distribution, if the equivalent luminance of this field is known under the same conditions of measurement.

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