Lumen (unit)
Lumen (Latin for light, lamp ) is the unit of luminous flux. As a photometric unit takes into account the lumen (abbreviated lm) the sensitivity of the human eye: Two identical light sources are perceived as equally bright when they emit the same luminous flux - regardless of their color.
The human eye has its maximum sensitivity in accordance with V- lambda curve at a wavelength of 555 nm ( yellow-green). One lumen is defined as the luminous flux of a strong 1,464 mW 555 - nm light source with 100% light output. A 1.464 mW strong red light source provides only about 0.1 lm, since the eye has only 10 % of its maximum sensitivity in the red.
The size of lumens per watt is often given as a measure for the luminous efficacy of a light source, because it is based on the useful portion of light by the human eye.
Formulas
The luminous flux is a measure of the total radiation emitted from a radiation source to visible radiation. Exuding a light source with a light intensity of I in a solid angle range of D? Then is the total luminous flux Φv:
For example, if an isotropic ( same in all directions ) radiating light source 1 Candela lights, ie transmits 1 lm per one steradian, one of the light intensity gets the luminous flux by the summation ( integral) over the whole solid angle surrounding the light source:
The illuminance measured in lux, can be converted into luminous flux and luminous intensity.
ANSI lumens
ANSI lumens is used when specifying the luminous flux of projectors (including video projectors) to say that the device according to the standard of the American National Standards Institute has been tested. The corresponding standard IT7.227 - 1998 but was withdrawn in July 2003 by the ANSI and finds himself no longer there. Valid, however, are virtually identical standards of " International Electrotechnical Commission (IEC) " as well as DIN EN 61947-1. In preparation for the measurement of the projector is set so that in front of a white background a 5% gray tinted field is indistinguishable from an 10% gray tinted box, two very light grays. The projection is then divided into three columns and three rows, and determines the average of the illuminance of all nine fields. The mean value multiplied by the projection gives the ANSI lumens.
In contrast to the illuminance of the luminous flux is independent of the size of the projected area. The information of most projector manufacturers refer to the standardized (formerly ANSI) maximum settings that are rarely optimal for the practice. The achieved with optimal settings for light currents are sometimes far less.