Rofin Polilight Flare PLUS, Руководство пользователя

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Polilight Flare Plus 2 manual –
11
FLUORESCENCE IMAGING
Fluorescence occurs when a substance absorbs a specific band of light (energy), turns part of the
energy into heat and then transmits the remainder of the energy out as new light. This new light
has lower energy and hence a different colour when compared to the original illumination light. The
intensity or amount of fluorescent light is always small compared to the intensity of the original light.
Example 1: Fingerprints treated with fluorescence powders or chemicals will fluoresce under certain
lighting conditions. This enables very faint fingerprints which could not be photographed under normal
light, to be captured with high contrast under fluorescent lighting conditions.
In the example shown in Fig. 4, the view under daylight conditions is on the left and the view when
illuminated with 450 nm Flare+2 head viewed through BP530 is on the right.
Figure 4. Fluorescence
Example 2: A number of substances and materials fluoresce naturally without any chemical treatment.
Semen, urea, fibres, grease, lipstick, paper, gunshot residues and inks are examples of materials that
can naturally fluoresce and hence be located on other background material.
REFLECTION IMAGING
Specular Reflection
A surface appears shiny because of specular reflection. The surface acts like a mirror and light hitting
the surface is reflected away at the same incident angle.
Untreated fingerprints or shoe prints on shiny surfaces can often be seen when viewed from a suitable
angle, so that light reflection to the eye or camera from the background is significantly different to the
reflection from the latent print ridges. Images can be captured from a variety of shiny evidence such as
cups, glasses, cans and knives.
Example: Untreated fingerprints on glass illuminated with low angle white light. As the glass is highly
reflective, the fingerprint looks black as no light is reflected from it towards the eye. Alternatively when
the light is ancident at a low angle the fingerprint ridges scatter the light and they appear bright against
the background.
Diffused Reflection
Some surfaces and evidence will reflect light in a diffuse manner known as random scatter. If evidence has
different reflection characteristics to its background it can be resolved under specific lighting conditions.
Light from the background is reflected at different angles. The sample may appear lighter or darker
compared to the background when viewed from above, depending upon the relative difference in
diffused reflections from the surfaces.
LIGHT APPLICATIONS