question for LHR technicians - spot size and fluence

For the technicians on this board, when a machine is set to 40J - that means 40J of energy per squared cm, right? So it should be a constant energy density regardless of spot size, correct?

I’m a little concerned about this because I am considering have more LHR done, and am debating between the GentleLase and the LightSheer. The GentleLase that I got a test patch done with had a huge spot size - if I’m remembering correctly it was rectangular and about 3cm by 2cm (although I’ve been for a number of test patches with different systems, so I could be getting them mixed up. Is it possible there was a different lens fitted over the handpiece? This spot size seemed massive.)

Do some machines have (removable) handpiece attachments that would cause the output energy to be distributed over a larger spot size, thereby decreasing the energy density? I’m a big fan of larger spot sizes, but not at the price of underpowered treatment.

Also, are fluence levels comparable between different types of machine? (ie. is 40J from an Nd:YAG equivalent to a 40J setting on an IPL or a diode laser?) I suppose it would depend on whether this power rating is measured at the device output or at the light generator - and whether some machines would be more lossy than others. I’d guess it would also depend on operating frequency - the higher the frequency of the light emitted, the higher the power you need for the same depth penetration. Any info here?

Fluences are not comparable between machines. Spot sizes on the GentleLASE are adjustable. The largest is usually 18mm which maxes out at 20 joules. 15mm maxes out at 30 joules, etc. There are different “heads” of various spot sizes that fit on. Large spot sizes cover larger areas, so the treatments are faster; also less chance of missing spots. Effective treatments are at 14-16joules and above.

LightSheer has a smaller spot size, depending on the model it’s 9mm or 12mm I believe. Joules are not comparable to the GentleLASE. Effective treatments at LightSheer is usually at above 25 joules. RC2001 has had good results with it at around 35-40 joules at least.

Thanks for the info. I had really been wondering about this.

Okay - I may be having a false memory here … but this is what I remember:

I went for a test patch at a GentleLASE clinic. The handpiece had a rectangular spot size (which I though was cool, because I always had concerns about overlap with a round spotsize - but I was also concerned about the transformation of a round beam into a rectangular footprint).

Anyways - the spot size seems massive; easily 2cm x 3cm. Which seemed great if I was going to do my entire body. However, looking on the manufacturer’s website - I could not find a handpiece with this spotsize, which confused the heck out of me.

In all honesty - it looked like they had put a rectangular attachment on the end of their handpiece.
Maybe I just need to pay them another visit. I could be wrong about all of this.

Does this sound familiar to anybody who has used a machine matching this spot size description?

I’m kinda obsessing about this because I have a fear of using too low of a setting on my first couple of visits and screwing myself over by just damaging the folicles and making the hair finer, rather than killing them.

you shouldn’t worry about this too much. first of all, you should find an experienced tech to do this, who would already know what settings to use. GentleLASE comes with various heads of 18mm, 15mm, etc heads. Low settings are under 14 joules on the GentleLASE. Whatever they use will be fine if it’s above that. And yes, overlapping is important, no matter which “head” they use. Bottom line, find someone who knows what they’re doing. These are very detailed things that don’t matter as much, especially if you find a good place. They need to overlap no matter what and you’ll be able to tell if they missed spots 3 weeks after the treatment, so you can ask for a touchup on those places.

The 12 mm spot size maxes out at 40 Joules. Big spot size is good but if your hair has become finer and thinner, you may then want to use a smaller spot size with higher energy in order to get the results you want.A smaller spot size concentrates more energy on the surface and would work better on finer hair, if your hair is finer.

A smaller spot size concentrates more energy on the surface and would work better on finer hair, if your hair is finer.

Thanks for the reply, but I’m not sure if I follow this part of it. Fluence is a measure of energy per unit area, ie. 40 Joules per squared cm.
My understanding was that spot size is limited at higher fluence settings because the machine doesn’t have the power to put out, for example, 40J/cm^2 over an 18mm diameter area (and maybe because putting out that much light energy into your skin per pulse has a greater chance of damaging you?)
I think a smaller spot size would work better with finer hair simply because you have upped the fluence and are bombarding it with twice the amount of light energy; rather than focusing the energy closer to the surface of the skin.
I don’t mean to be splitting hairs, just want to make sure my understanding of this is correct.

Both are correct. Finer hair is closer to the surface so you do not need a bigger spot size to go deeper. Also, a smaller spot size allows you to use higher fluences.