Inverse Square Law

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A formula relating the illuminance (E) produced on a plane surface element at a given distance (x) from a light source to the luminous intensity (I?1) of the source in the direction of the element. If the normal to the element makes an angle ?2 with the direction of the incident light, the law may be expressed as


In this form, the cosine law of illuminance is also expressed.

Ch2 Fig4.jpg

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



charge current


nertia of the water plane

International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM