If the source emitted uniformly in all directions, the total radiant flux would be about 18.40 mW, since there are 4π steradians in a sphere. Lux is basically the unit of illumination and is equal to one lumen per square metre. y Light intensity at the product surface, described by the term irradiance, is a measure of momentary exposure and is most often quantified in milliwatts/cm2. Its value is similar to candela as well. Lux (lx) Unit of … While it can get quite complicated, let’s look at some of the few measurement units below. 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Candela is the basic SI unit of luminous intensity. The output of artificial lights can be measured in lumens. a unit adopted in 1979 as the international standard of luminous intensity, defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 x 10 12 hertz and that has a radiant intensity of 1/683 watt/steradian. Luminous intensity should not be confused with another photometric unit, luminous flux, which is the total perceived power emitted in all directions. The energy unit of light intensity is generally expressed by J/m2 and mJ/cm2, that is, the light energy per unit area. λ Unfortunately there are many different units used to measure intensity: lumens, candle power, watts/m^2, etc. The curve which measures the response of the human eye to light is a defined standard, known as the luminosity function. 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