Stranica 57 [57]
OCR
CHA, BR 7 Grant Agreement n" 228330 examination location) should also be carefully controlled, as they can significantly interfere with the interpretation of the luminescence. Filter in front of the camera: For UV-reflected images a filter is reguired which will block radiation in the visible and IR regions (400 - 1100 nm). This would reguire a filter with properties similar to the Schott glass DUGI1IIX filter (see Figure 2-8 for transmittance curve and recommendations for alternatives above). 1e+0 BLB UV lamp 1e-1 Excitation wavelength 10-2 300 — 385400 500 600 700 800 900 1000 wavelength (nm) 350 400 700 1100 Wavelength range of a typical camera CCD/CMOS sensor Figure 2-7. Schematic representation of the spectral output distribution (SPD) of a BLB ultraviolet light compared to the wavelength range of a CCD/CMOS sensor. Shading shows wavelengths to be excluded (filtered) in the acquisition of UV-reflected images. Note that although the sensitivity of camera sensors is typically 200 — 1100 nm, the range will be attenuated to the quoted 350 — 1100nm (in the modified cameras described in this work) because of the widespread use of glass lenses. This would yield “UV-reflected” images in the range 350 — 400 nm, with the filters recommended above. In order to collect images that can truly be referred to as UV-reflected, quartz lenses would need to be used, which would make the range of acquisition of these images) approximately 225 — 400 nm with the filters recommended above. However, it should be noted that the sensitivity of camera sensors drops off significantly at the extremes of its wavelength range (see Figure 2-2). Version No. 1.0 49 Date : 14/10/2013
