Join Date: Aug 2006
Location: Christchurch, New Zealand
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For what it is worth, the calibration industry is semi self regulated with foundations in the USA which intern follows imperial measurement, typically fl =foot lambert and hence the domination of the term fl used in calibration software.
The international SI unit is cd/m^2
Lumen (lm) is also an SI unit, and so is Lux (lx)
1Lux = 1 lumen/m^2 (abreviated as 1 lx =1 lm/m^2)
(m^2 = metre square)
1Lux = 1 cd/m^2
Lux is a measure of intensity as perceived by the eye
The difference between Lumen and Lux is that Lux takes into account the spread of luminous flux over an area such as a screen.
Lumen is output from the projector, Lux is what you see as a whole.
The standard method for screen measurement is based upon luminous flux per solid angle, candela per area, which brings us back to footlamberts (fl) for US motion picture industry or SI-unit(international standard) candela per square metre (cd/m^2)
For home theatre it is typical to find (10fl)(34cd/m^2)~(14fl)(48cd/m^2) range, even as low as (7fl)(24cd/m^2) when bulbs age.
Masterpiece Calibration Ltd