A multilayer filter was used in conjunction with varying the separation between the source and solar cell to enable the desired illumination levels to be achieved. The filter material was used to add additional attenuation in the case of sources which provided a higher illumination level than was required at the target with the source and solar cell at maximum separation.
The filter material used shows a uniform spectral response over
the spectral range of 400–900 nm,
Fig. 6 shows the relative spectral power of the incandescent lamp when a number of different layers of filter were added between the source and the spectral measurement, the relative spectral powers have been normalised to the direct, non-filtered, values.