Allard's Law

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2-1-265

A formula relating the illuminance produced on a normal surface at a given distance from a point source of light, the intensity of the light and the degree of transparency of the atmosphere (assumed uniform).

The law may be expressed as follows

Allard1.gif

where E is the resulting illuminance on this surface

I is the intensity of the incident light in the direction of measurement.

T is the atmospheric transmission factor (assumed uniform) for specified Unit: distance.

x is the distance of the surface from the light source, measured in the specified units of distance.


Note: Another form of Allard's Law is

Allard2.gif

where V = meteorological visibility (2-1-280 and 2-1-290, Note:).




Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)

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