Accurate assessment off₁′ value of fine photometer heads

Abstract

For an accurate assessment of the f 1 value of a photometer head it is important to determine the maximum step size for sampling and an appropriate bandwidth of the monochromator for an acceptable uncertainty contribution. A simulation is carried out to evaluate these uncertainty contributions for fine photometer heads, with a mismatch characteristic f 1 3% and uncertainty contributions f 1 0.1% taken as the limits for acceptance. Assuming a stable measurement set-up, the results show that a 5 nm step size and a 5 nm bandwidth or less are needed for this assessment. The uncertainty of the f 1 value caused by the wavelength uncertainty of the monochromator is analysed additionally. For extended bandwidths a method is proposed to correct the spectral responsivity data of the photometer head and reduce the bandpass uncertainty contribution effectively.

Spectrometer bandwidth correction for generalized bandpass functions

“…The effect of bandwidth has been investigated for determining the irradiance of LED and fluorescent sources [1,2], for determining the colour of materials [3] and for determining the responsivity of photometers [4]. For example, when measuring an LED with a spectral width of 25 nm using an instrument with a 5 nm bandwidth triangular bandpass function, the measured peak height is reduced by approximately 2% and the spectrum is broadened compared with the true spectrum.…”

LED near-field goniophotometer at PTB

“…In In order to evaluate the matching index between the luminous intensity distributions obtained from near-field and far-field measurements, the matching index f I is calculated using equation (10), see equation in table 1.…”

“…the average deviation is 3%). It has to be pointed out that both matching indices shown in equations (10) and (11) only describe a method to compare (displayed) values. However, these matching indices are not suitable to describe the quality of the measured quantity, because the physical difference between the radiation transfer expressed e.g.…”

“…Moreover, by substituting the photometer 2 with the fibre optic entrance of a spectroradiometer mounted on the rotary stage (see figure 4) adjacent to the photometer, the light source can also be spectrally characterized in the far field. This is necessary to correct the spectral mismatch of the detectors (camera and photometers) calibrated with respect to illuminant A [9,10].…”

Stray light errors in spectral colour measurement and two rejection methods

“…Neither the correction method nor the filter-wheel technology can reject the errors caused by the bandpass of the spectrometer. To correct the bandpass errors, the methods in [9,10] can be used.…”