Page 72 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
 Figure 37: Light in the skin - Source: ANDERSON RR, PARRISH JA.
The Optics of Human Skin. The Journal of Investigative Dermatology 1981; 77:14.
Let’s go through these one by one......
Absorption
● ‘White’ light is a mixture of many wavelengths. The human eye cannot discriminate these colours, so, we ‘see’ white.
● However, when white light falls onto a surface some of the energy is absorbed by the atoms/molecules.
● The remaining energy is either transmitted through the material or reflected back into the environment.
● The reflected energy will contain only those wavelengths which were not absorbed by the material – this determines its ‘colour’ (see figure 38 below and animation).
  Absorption can be thought of as a ‘subtraction’ process – the object which is illuminated by the light will absorb, or subtract out, some of the incident wavelengths.
This is a photo-chemical process which depends on the atoms in the object.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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