Most people can see a wide range of coloured light, from around 350 up to 750nm. But, our sensitivity is not the same for all colours.
Our human retina sees different colours differently. The graph below shows how this is – we see violet very poorly. Likewise with the ‘deep’ reds, out at 700+ nm.
The y-axis (on the left) is a logarithmic scale – 100 is 1. We call this a ‘normalised’ graph. All the sensitivities are related to 1. The graph shows that we see the green wavelength at 555nm, better than all other colours (obviously, there will always be a variation between people depending on various factors). So, this measurement is set to the maximum of 1.
Violet light drops from a sensitivity of around 0.04 (at 455 nm) to zero (at 375 nm) – in other words, at best, our sensitivity of violet is only around 4% that of green at 555nm. We can hardly see this colour! Blue is a bit better – we see it from a sensitivity of 0.04 up to 0.2 (at 490 nm).
This means that even our ‘best’ view of blue light is still only around 20% that of green at 555 nm.
At the other end of the spectrum, we see red from around 0.3 (at 625nm) to zero.
This might be surprising, but it’s what we’re used to. We don’t realise that our violet, blue and far red vision is so poor, because we don’t know it!
How does this relate to lasers and treatments?
Well, it means that we are really quite poor at ‘judging’ colours in the skin. To add to that poor judgement, dermal scattering doesn’t help either!! It just confuses the matter even more.
As a consequence, we have to realise that our eyes are often not a good indicator of what is actually going on in the skin. When we see some colours, we may ‘perceive’ some particular colour, but it might easily be something else, which we simply cannot detect with our puny vision! However, laser and IPL light energy will “see” those colours as they are, and trigger the various responses accordingly.
Oh well, never mind…
Mike.
Mike Murphy's Blog 