Allard's Law: Difference between revisions
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'''2-1- | '''urn:mrn:iala:dic:2-1-0265''' | ||
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). | 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). | ||
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The law may be expressed as follows | The law may be expressed as follows | ||
[[File:Allard1.gif]] | |||
where E is the resulting illuminance on this surface | where E is the resulting illuminance on this surface | ||
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I is the intensity of the incident light in the direction of measurement. | I is the intensity of the incident light in the direction of measurement. | ||
T is the atmospheric transmission factor (assumed uniform) for specified | T is the atmospheric transmission factor (assumed uniform) for the specified unit distance. | ||
x is the distance of the surface from the light source, measured in the specified units of distance. | x is the distance of the surface from the light source, measured in the specified units of distance. | ||
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Note: Another form of Allard's Law is | Note: Another form of Allard's Law is | ||
[[File:Allard2.gif]] | |||
where V = meteorological visibility (2-1-280 and 2-1-290, Note | where V = meteorological visibility (2-1-280 and 2-1-290, Note). | ||
{{IALAFooter}} | {{IALAFooter}} | ||
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[[Category:Alphabetical Index]] | [[Category:Alphabetical Index]] | ||
[[Category:IALA Dictionary 1970-89 Edition]] | [[Category:IALA Dictionary 1970-89 Edition]] | ||
[[ | [[Category:IALA Dictionary 2023 Revision]] | ||
Latest revision as of 08:06, 17 September 2026
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
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 the 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
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)
