A lumen is a measure of radiant light emitted by a light bulb. A candela describes how much luminous energy a bulb emits per second in a given direction. Luminance, generally expressed in foot-lambert or candelas per square meter, measures the amount of light emitted by a surface. The candela is a light level based on the light produced by a single lit candle. The American National Standards Institute bases the lux light measurement on one candela of brightness. A lumen equals 1/683 watt at 555 nanometres of radiant flux.
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Things you need
Calculate the screen area in square meters.
Measure the incident flux in lux (lumens per square meter) with a photodetector. According to Charles Swartz, ANSI requires the measurement of flux in nine areas of the screen.
Average the nine incident flux measurements to determine the average incident flux.
Multiply the average incident flux in lux by the screen area to calculate the projector's output in lumens.
Locate a photodetector rated for the light wavelength to be measured. According to "International Encyclopedia of Ergonomics and Human Factors," lumens may be measured using a photodetector, based on either a current or a voltage in response to the rate of incident electromagenetic energy or light.
Calibrate the photodetector for the wavelength of light to be measured or determine the wavelength of light to be measured and apply an adjustment factor from the 555 nanometre standard.
Measure the lumen level of the desired light source with the photodetector. If the photodectector has already been calibrated to the light wavelength, no further action is necessary.
Tips and warnings
- According to "Automated Lighting" by Richard Cadena, the specification for the ANSI lumen is no longer supported by ANSI as of 2003; however, it is still in widespread use in the projector industry. The ANSI standard for lumens was directly replaced with IEC standard 61947-1. So if you have the IEC lumen measure, you have the ANSI lumen measure.
- ANSI standard C78.377 gives the recommended chromacity or colour range for white-light-emitting diodes. ANSI standard C82.77 lists the acceptable power quality requirements for all solid state lighting. ANSI standard RP-1 gives the recommended lighting levels for offices.
- According to "International Encyclopedia of Ergonomics and Human Factors," the candela is defined as watts of 555 namometer radiant flux per steradian without reference to a particular source.
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- "Automated Lighting"; Richard Cadena; 2010
- "Introduction to Human Factors and Ergonomics for Engineers"; Mark Lehto, James Buck; 2007
- "International Encyclopedia of Ergonomics and Human Factors, Volume 1"; Waldemar Karwowski; 2006
- "Understanding Digital Cinema"; Charles Swartz; 2004
- "Smart Guide: Basements"; Mark Feirer; 2003