The luminous flux (english luminous flux ) is the photometric equivalent of the radiation power. He is lumen ( lm) given in the unit, taking into account the wavelength-dependent sensitivity of the human eye. The integration of the light intensity over space yields the luminous flux. The integration of the current over time results in the amount of light.
Luminous flux determination using an integrating sphere ( sphere photometer )
The common, but relative measurement using an integrating sphere leads to a relatively rapid results, which is present in Millisekunden-/Sekundenbereich. Taking into account the preparation time, as controlled aging ( 48 hours for halogen lamps) or thermal stabilization (2 h for LED luminaires and lamps) of the light source, the time advantage, however, reduced. A device attached to the integrating sphere photometer / spectrometer allows instant reading of the luminous flux. Precise measurements are carried out under two conditions. The ( relative) measured ball must have been calibrated by a suitable light source identical spatial radiation, since the light mixing is not sufficient in common photometer color ( inner lining of the ball ). An increase of the reflectance to values of greater than 90 % is no longer recommended by the CIE, as the long- time stability can not be ensured by inevitable dusting the lower half of the sphere. Furthermore, the ball must be either calibrated with a known light source spectral distribution of identical or the entire system " ball with mounted photometer head " must be similar to a spectral sensitivity have luminous efficiency function of the (human ) eye. This claim, however, is (fast read ) only for photometers with partial filtering and spectrometer ( much slower readout) satisfiable with integrated light scattering matrix correction. In summary it can be stated that the ball provides excellent measurement results when " equal to equal " and is thus relatively measured. Course, the spatial or spectral radiance or the design of the calibration light from the measuring object, the measurement uncertainty is significantly increased.
Luminous flux determination of the light intensity distribution ( Goniophotometer )
The much more accurate, because an absolute measurement of the light flux is mounted on a goniometer performed using an illuminance measuring head. The goniometer moves the photometer head (actually illuminance measuring head ) on a virtual spherical surface around the measuring object. Depending on the distribution of the angle-dependent intensity of the light source, the measuring time is in the range of minutes / hours. It is important to mention here that works to be measured, the light source via the measuring time stable. The goniometer driven by the railways have a historical background on rhumb lines ( spiral paths ) or form large circles / small circles after. If the light intensity distribution ( LID ) partially known, every conceivable grid can be scanned and thus the temporal measurement costs considerably reduced by CNC. If upon completion of the measurement value recording before a meaningful spatial distribution of the measured values , it is possible with the help of numerical methods to compute the luminous flux from the light distribution. As with the measurement of the sphere photometer spectral adjustment of the measuring head is important, according to DIN 5032 Part 7 results in a Class L measuring head only at a total error of less than 1.5 %. The use of illuminance measuring heads with partial filtering is necessary. Furthermore, make sure that a sufficiently narrow measurement grid.
Calculation of the spectral flow
To evaluate the light sensitivity of the human eye, the spectral flow is pointwise (per wavelength ) multiplied by the sensitivity curve. This is the photometric radiation equivalent. The integral over the wavelength Ultimately, the luminous flux