Operation Manual

144 GMC-I Messtechnik GmbH
Appendix
Basic Light Technology Theory
Illuminance indicates with how much intensity an area is illumi-
nated. The unit of measure for illuminance is the lux (abbreviated
lx). The lux is defined as follows: a light source with a luminous in-
tensity of 1 candela (abbreviated cd) at a distance of 1 meter has
an illuminance value of 1 lux. The candela represents luminous in-
tensity in a specific direction from the source of radiation which
emits monochromatic radiation with a frequency of 540 x 10
12
Hz, and whose radiant intensity in the direction in question is
equal to watts divided by steradian (1/683).
The footcandle is another unit of measure for illuminance, and is
especially common in England and the USA. The footcandle is
equal to illuminance resulting from a light source with a
luminous intensity of 1 candela at a distance of one foot.
The following relationships exist between the lux and the footcandle:
1 footcandle = 10.76 lux
1 lux = 0.0929 footcandles
Correct measurement necessitates an evaluation of the emitted
light on the basis of eye sensitivity in accordance with
internationally standardized spectral sensitivity V() of the light-
adapted eye. This curve represents the mean value which has
been ascertained with a large number of test persons.
The utilized silicon photo cell has been adapted so closely to the
spectral sensitivity of the human eye by means of correction
filters, that it can be assigned to accuracy class B in accordance
with DIN 5032, part 7, for the MAVOLUX 5032 B USB.
Further details are included in DIN 5032.