Figure 2.

(a) Spectral content of the ceiling light, measured as the reflection from MgO-coated surface using a calibrated spectrometer (HSU-100S, Asahi Spectra, Tokyo Japan). (b) Spectrum of Xe light measured from the inside of the cage after passing through the diffusing screen without having other filters shown in C and D. (c) Transmittance spectra of neutral density (ND) filters. (d) Transmittance spectra of colour and polarization filters: B, blue; I, indigo; O, orange; P, pink; R, red; V, violet: POL, polarization filter.