Page 186 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The skin colour is hugely significant! Darker skins have much more melanin in the basal layer of the epidermis. This will absorb some of the incoming light energy – ‘black’ skin (ST6 absorbs around 6 times as much of this light energy as very pale skin, ST1. Not only does this reduce the amount of energy available for the hair, but it also over-heats the epidermis.
In addition, the skin colour also determines how light is backscattered out of the skin altogether. So, after all these losses, how much fluence is left to heat up the hair?
Table 45 shows that the loss of light energy can be very significant by the time it reaches the hair. It also shows the differences between different filters and skin colours.
Wavelength range (up to 1200nm)
ST1
ST6
400nm
67%
38%
500nm
56%
37%
600nm
45%
33%
700nm
36%
29%
Table 45 – The amount of light energy which can heat up the hair follicles
These losses must be taken into account when treating hair in different skin colours. 20 J/cm2 of IPL light using a 700nm filter in a very dark-skinned person is quite different to 20 J/cm2 with a 600nm filter in a pale-skinned person! In fact, the above table shows that only 5.8 J/cm2 will reach the hair in the dark-skinned person, while 9 J/cm2 will reach the hair in the pale-skinned person.
Figure 87 – IPL filter for hair removal in light skin
________________________________________________________________________ 186 Chapter 3 Laser/IPL Hair Removal
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