COMPARABLE BRIGHTNESS OF H³ LIGHT SOURCES

A simple method of expressing the intensity (or level of brightness) of GTLS (Gaseous Tritium Light Source) devices is to compare them with known objects and scenes, as in the following table:

Approx. Brightness (in Foot-Lamberts)	Comparable Visual Object or Scene	Approx. Text-Effect
100,000	Upper limit of visual tolerance	BLACK - GREY - WHITE
10,000	Fresh snow on a clear day	BLACK - GREY - WHITE
1,000	Average earth on a clear day	BLACK - GREY - WHITE
100	Average earth on a cloudy day	BLACK - GREY - WHITE
10	White paper in good reading light	BLACK - GREY - WHITE
1	White paper 1 foot (34cm) from standard candle	BLACK - GREY - WHITE
0.1		BLACK - GREY - WHITE
0.01 (= H3 upper)	Snow in full moonlight	BLACK - GREY - WHITE
0.001 (= H3 lower)	Average earth in full moonlight	BLACK - GREY - WHITE
0.0001	Snow in starlight	BLACK - GREY - WHITE
0.00001	Grass in starlight	BLACK - GREY - WHITE
0.000001	Absolute threshold of sight	BLACK - GREY - WHITE

GTLS devices are measured by luminous intensity rather than brightness. The term "brightness" is merely the degree to which a unit surface area appears to emit light in the direction of an observer.

For GTLS devices, the corresponding physical measurement of the light actually emitted is called the luminance. This is the measure of the light actually emitted (i.e. the luminous intensity) per unit projected area of surface, the plane of projection being perpendicular to the direction of view.

In engineering, the luminance of an ideally diffusing surface emitting or reflecting one lumen per square foot is called one foot-Lambert (ft-L). And on this scale, H³ light sources [ie. tritium/hydrogen lamps] lie between 0.01 and 0.001 ft-L (equivalent to full moonlight, as in the above table).

For more, read Permaglo Signs: Intensity of GTLS Devices.