The fluorescence which is stimulated an ultraviolet radiation is a special form of the luminescence. Thereby, electrons of fluorescent molecules reach a higher energy level by absorbing photons. Such a stimulated condition is energetically unstable. The electrons return immediately into their ground state where the absorbed energy is released again. At the same time an emission of the fluorescence light takes place. Due to the fact that a part of the energy is dissipated into heat, the emitted radiation has less energy and so a longer wavelength. The wavelength of the emitted light is belongs to the range of visible blue light and depends on the absorption curve and the strokes displacement. Organic materials which are exposed to the UV light, often show a high self-fluorescence. For this reason it is possible to detect contamination in the form of oil and grease films as well as surfactants on surfaces. Furthermore, you can detect defined wax and corrosion protective layers as well.

When fluorescent-active materials get excited to fluoresce, it comes to the so called photo-bleaching effect. The lifetime of fluorescent molecules limited due to an irreversible photochemical processes. The photo-bleaching effect is caused by a photo-oxidation where excited molecules with molecular oxygen from the ground state react in a chemical destruction process. This chemical destruction process produces excited singlet-oxygene where the electrons of the oxygen reach a higher energy level. Under this condition, the molecule can be oxidized irreversibly from the oxygen. The lifetime of excited fluorescent molecules depends on the intensity of the excited radiation and the temperature.
The SITA CleanoSpector was designed in a way so that the detecting duration of one measuring point does not provoke a significant photo-bleaching effect in general. If you repeat the detection of the cleanliness at one point, it happens that the device displays an increased cleanliness value.

An increase of the measuring distance causes an increase of the excited surface and a decrease of the intensity of the excitation radiation. Furthermore, the part of the detected fluorescence radiation decreases as well because it is emitted diffusely in all directions. For this reason, the intensity of the measured fluorescence decreases and the output cleanliness rises.
A decrease of the measuring distance causes an increase of the detected fluorescence radiation so that the output cleanliness decreases. The measuring distance (end cap – part’s surface) should amount to 4 mm +- 0,5 mm. If you want to use spacer, you should position them on the surface.