General About Illuminance; The Origin Of Light; Radiometric And Photometric Values; Basic Photometric Definitions - Benning B Handbuch

.1 Main application standards for field illuminance (lux) meters
There is a series of DIN (German Industrial Standards) standards with detailed
descriptions (definitions, precautions, measurements, worst values etc) of light
measuring in different privat and public places.
DIN 505 Illumination with artificial lights
- general precautions, measurements,
- terms, definitions and calculations,
- illumination in hospitals, schools, working places, offices,
- illumination in places with screens.
DIN 504
Daylight in indoor rooms
- general precautions, measurements,
- terms, definitions and calculations,
- definition of minimum window size apartmans and loft rooms.
DIN 507 Headlights
DIN 5044 Traffic illumination with street lights
DIN 400 Workplace definition
DIN 6756 Lighting for sport facilities
. General about illuminance
.1 The origin of light
Light is a part of the electromagnetic waves. The electromagnetic spectrum
covers an extremely broad range, from very low frequencies or infra-frequen-
cies over the radio waves with wavelengths of a meter or more on one side, to
x-rays and gamma-rays with wavelengths of less than a billionth of a meter. But
the part of the light which we are interested in is the optical portion of the elec-
tromagnetic spectrum (Figure 1). It lies between radio waves and x-rays, to be
exact, it borders on infrared light on one side and ultraviolet on the other.
UV-C UV-B
Ultraviolet light
X-rays
100-380 mm
Figure 1:
. Radiometric and Photometric values
The two approaches on how to measure light are:
- radiometric (based on energy),
- photometric (weighted to match the responsivity of the human eye).
The values that are weighted to match the responsivity of the human eye
(luminous flux, illuminance, luminance and luminous intensity) are measured by
photometric light units, the others (radiant flux, irradiance, radiance and radiant
intensity) by energetic units.
The lumen, for example, is the photometric equivalent of the watt. If one wants
to measure visible light, one must use photometric quantities. If one wants to
measure energy of light, one must use radiometric quantities.
. Basic photometric definitions
Luminous Flux P [lm]
Luminous flux is a measure of flow of visible light. The unit of the measure is
Lumen. There are two kinds of luminous flux:
- photopic flux (weighted to match the responsivity of the eye in normal light
condition)
- scotopic flux (weighted to the sensitivity of the human eye in the dark
adapted state)
Luminous intensity I[lm/sr]
Luminous intensity is a measure of luminous flux emitted per unit solid angle.
The unit of solid viewing angle is steradian. One steradian covers one square
meter on the surface of a sphere of 1 meter radius.
Illuminance E [lm/m2=lux]
Illuminance is the density of a luminous flux incident on a given point on a sur-
face and is measured in Lux. 1 Lux is caused by a light source with the intensity
of 1 candela at the distance of 1 meter.
Luminance L [lm/m2/sr=cd/m2]
Luminance is a measure of luminous flux emitted from an element of a surface
into a small solid angle per unit of projected area of the surface.
01/ 2007
UV-A
Visible light
380-770 mm
Electromagnetic spectrum
BENNING LUXMETER
Infrared light
770 mm - 1 mm
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Microwaves
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