Page 219 - Blog Posts v1

E9 - How much light energy actually emerges from IPL filters and reaches the skin surface?
When we set a fluence on an IPL unit, it is based on ALL of the light energy coming from the handpiece. However, each filter will absorb some of that energy – it is supposed to! The filters are designed to ‘block’ certain wavelengths, so that only the desired wavelengths reach the skin surface.
So, to effectively treat blood vessels, we must apply green and yellow wavelengths. Hence, a filter in the region of 500 to 550nm is necessary for this treatment.
But, how much light energy is absorbed by these filters?
I built a computer model based on the spectral output of a Xenon lamp to answer this question. This model allows me to calculate the amount of energy will be absorbed by filters, based its distribution across the wavelength range 350 to 1200nm.
The table below shows how much light gets though each filter:
Filter cut-off wavelength (nm)
% light energy emerging
400
88%
500
75%
600
65%
700
51%
This is very interesting! Only 51% of all the light energy above 700nm gets through the filter. So, if the fluence on the screen is set to 20 J/cm2, then the actual energy emerging from the filter is only about 10 J/cm2.
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