Forensic dental photography 205
11.3 Properties of Illumination
When an object is illuminated with white light, four phenomena take place.^4
Reflection occurs when electromagnetic radiation strikes and bounces back
from the object. It is this reflection of visible light that accounts for the colors
seen by the human eye. Not all light energy that strikes an object is reflected.
Some of the light can be absorbed. It is the absorption of all colored light by
an object that makes that object appear black. A third reaction that occurs,
especially when light strikes human skin, is the transmission and scattering
of the energy associated with the light through successive layers of cells until
the energy of the light is spent and has dissipated. The final reaction, which
occurs when light energy strikes an object, is a molecular excitation called
fluorescence (Figure 11.1).
Table 11.1 Spectrum of Electromagnetic RadiationWavelength (nm) Defined Light
0.1 x-rayUltraviolet0.7 μm 0.6 μm 0.5 μm 0.4 μm
InfraredVisible Light Region
of the Electromagnetic Spectrum250–375 Ultraviolet
400 Violet
470 Blue
530 Green
600 Yellow
700 Red
750+++ InfraredWavelength (nm) Defined Light
0.1 X-ray
250–375 Ultraviolet
400 Violet
470 Blue
530 Green
600 Ye l l o w
700 Red
750+++ Infrared
Source: Data from Kochevar et al.,^4 with permission. Color
spectrum image from http://www.science.hq.nasa.gov/kids/
imagers/ems/visible.html.