Luminous exitance

Luminous exitance (Luminous emittance)t M, (M ) M = d(t>ldA lumen per square foot Im/ft ... 

In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance. In Sl-derived units, these are both measured in lux (lx) or lumens per square meter (cdsrm ). In the CGS system, the unit of illuminance is the phot. One phot is equal to 10,000 lx. Illuminance was formerly often called brightness, but this leads to confusion with other uses of the word. 

Hydrogen forms three isotopes protium, deuterium, and tritium. Protium and deuterium can be separated by a variety of physical and chemical processes. Ordinary light hydrogen in H-X bonds can be replaced by deuterium, which then provides a means of following the progress of a variety of reactions. Heavy water is used as a moderator in fission reactors. Tritium, produced naturally in the upper atmosphere and artificially in fission reactors, is a mild beta emitter and is used as a tracer and to make luminous paints and self-luminous exit signs. 

New example of tritium in self-luminous exit signs... 

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