I understand that it’s J/cm^2, but when I read studies, it seems that most of them refer to fluences of 30-50. For a Candela GentleLase, 20J is the highest setting for an 18mm spot size. 20/25.4…that’s about .78. I’m guessing that’s probably not the fluence. The pulse duration is automatically set on this machine, but I don’t quite remember what that is. So…
How do you figure out what the actual fluence is?
Hmm…Well I was going to edit the thread and title to be something like “A couple of questions,” but it seems like you can’t edit threads once they reach a certain age.
Anyway, I had a quick question I wanted to add to the above.
I had a test spot done (GentleLase 18mm spot 18J)–which I tolerated well. Any redness subsided quickly, and within 24 hours, there’s no sign that the area was treated at all. It’s neither sensitive, sore, nor red.
How long should I wait to see if that was effective before I commit to a full treatment? It will be some weeks before I see any shedding. How does it work? I wait 2 weeks and, if I see shedding, I’m good to go? Or, should I wait a full 8 weeks or so to see if there is a noticeable reduction compared to surrounding areas?
Note, what I’m considering is just a single treatment. I’m not committing to a plan unless the single treatment is effective. Packages come in 5s, and I’m mostly likely going to take more than that to get me where I want to be.
Hmm… Fluence is measured in terms of units of J/cm2 in hair removal studies. That means you should not be bothered by the spot size; it is just because spot size is defined as a measurable amount by units of length. F.e. when they A fluence for x spot size, and B fluence for y spot size; it means Ax total energy for the former, and By total energy for the latter. So, IN TERMS OF DELIVERED ENERGY, if you keep the fluence constant and increase the spot size, you increase the energy directly proportional to the area. Let’s say we have 20J/cm2 fluence, and two different spot sizes: one with diameter 9mm and one with diameter 18mm. You would deliver 4 times much energy with 18mm one as you would do with 9mm one.
The above example may be deceiving and confusing as we look at the manufacturers’ recommendations as they say, effectiveness of the treatment is similar in “high fluence with small spot size” and in “low fluence with large spot size”. I mean, 20 J/cm2 with 18 mm spot size is regarded as comparable to 30 J/cm2 with 12 mm spot size (I improvised the numbers). So, what on earth is wrong with the manufacturers? I think this oddness is due to the fact that once the laser beam hits the skin it penetrates into the skin, but not in a direction parallel to the original laser beam direction. It instead scatters all around at different angles. The scattering contributes to deeper penetration as the spot size increases, and as the hair follicles targeted lay at a distance beneath the surface of the skin, same fluence of laser appears to be more effective if a larger spot size is used.
By the way, you made a calculation mistake above; it should be 20/2.54 instead of 20/25.4.
How long you should wait to decide if a treatment was effective or not? I am male 28 y/old with coarse hair all over. Based on my experience, at %90 percent of the time you should be able to tell right after the treatment instantly. In my early treatments, I mostly experienced expelling of hair off the skin during the treatment. As the treatments progressed I started to see burned hair trapped in the skin known as the pepper-dots. Very occasionally ,for relatively finer hairs, I witnessed hair seemed to stop growing rather than appearing obviously burned, but in a couple of days its attachment to skin either got loose and eventually I was able to easily pull it off without encountering any resistance or stayed rigid and for some later it resumed its growth as if it awakened from a dormant state. So, I would say, wait for a week and observe those seem to be growing, they are either the ones on the course of being ejected or continue normal growth. By the end of 1st week, if there is a considerable number of hairs growing and not easily be pulled off, then the odds are the treatment didn’t do the job.
Ah, I see. So, actually the setting “20J” isn’t 20J, but actually 20J/cm^2.
That means that the calculation to determine the actual energy is:
20 J/cm^2 = (X J)/(area of spot size in cm^2)
Thus, X J = (area of spot size)*(20 J/cm^2)
where 20 J/cm^2 is the setting for the treatment.
Hmm…Now that I see that the 18mm spot size is a circle, determining the area is slightly different than I thought at first. Is it actually 18mm^2 or is that the diameter of the circle?
If it’s the diameter, then the area is 9mm^2 * 3.14 or 254.34 mm^2…Or as Vklepil pointed out 2.54 cm^2.
And you’re at 2.54 * 20 = 50.8J.
Not really sure.
At 15mm spot and 30J/cm^2, you’d be at 1.76 * 30 = 48 J. So, you actually hit slightly higher energy at the higher spot and higher fluence than you would with the 15 spot…If that’s really the max fluence for a 15mm spot on a GentleLase (as I think I read)…and assuming the rest of my math is right ><;
edit: found out max is 30J/cm^2 (not 35) for 15mm spot on gentlelase
Theofod: 18mm @ 18j is proper settings for good results. If you do not have success it would be because you are a part of the very small group of non responders. Those chances are slim. Having one treatment is a good idea, although the pain is going to be more intense for the entire back. Hopefully that will not stop you from continuing your treatments.
Max joules on Gentlelase 15mm is 30j --The main difference is number of pulses. 15mm is going to be a lot more pulses and more time on the table. Less pulses, less time on the table is ideal for you and the practitioner.
Vkl when the laser penetrates the skin it does so in a cone fashion forming a point at the tip. I will try to find some published details on the web.
There is nothing wrong with your math. 18mm spot size means the spot size diameter is 18 mm. That said, I don’t see what kind of analogy you actually try to establish with the following:
At 15mm spot and 30J/cm^2, you’d be at 1.76 * 30 = 48 J. So, you actually hit slightly higher energy at the higher spot and higher fluence than you would with the 15 spot…If that’s really the max fluence for a 15mm spot on a GentleLase (as I think I read)…and assuming the rest of my math is right ><;
15mm and 18mm spot sizes are in different leagues, I don’t think we should reach to conclusions comparing the total inflicted energies. With smaller spot size you deliver slightly lower energy to a smaller area. What could we make it out of this info? I am not sure.
However, your comparison makes sense and gives us a clue that your calculation and understanding in correct in the sense they are actually close and it tells us the laser device has a capacity of producing of ~50 J per unit time.
As I said in the previous post, thicker beam penetrates deeper, so at a unit section, beneath the skin, parallel to the skin surface and at a fixed distance from the skin surface, you should see more photons crossing the section at the larger spot size given that we use the same fluence level for the larger and the smaller spot size.
Well, when I thought that the max fluence for 15mm was 35 J/cm^2, the post made more sense. If it were 35, the total energy would be approximately 62J, and that’s much higher than the 18mm spot size @ 20 J…But it’s actually 30, so that’s a lost point.
Vkl when the laser penetrates the skin it does so in a cone fashion forming a point at the tip. I will try to find some published details on the web.
This is what I would expect. So, it explains clearly why larger spot size works more effective. It is because of the distribution of scattered photon once the laser beam hits the skin. At a fixed distance below the surface you should see most number of photons at the center. As you deviate away from the center the number of the photons at each point should decrease. As we were to put number of photons at each point in a graph, the graph would resemble a ring-bell curve. And, let’s assume that we have a certain threshold and that is the number of photons we should observe at a specific point to destroy a hair follicle. Let’s us denote this threshold as N. So, you have a smaller sized spot beneath the skin than the actual spot. I call this the “effective spot size” (ESS). ESS does not include any point lower than N. Now, let me come to the conclusion, why we observe similar results with “large spot size - low fluence” and “small spot size - high fluence”. But before, a couple of definitions:
A: size of the large spot
B: size of the small spot
a: ESS of the large spot
b: ESS of the small spot
It is because a/A > b/B. It can easily be proved, but it is more practical to see it by intuition.
I think you should revise everything from the beginning. Why should we have higher total energy for 35j/cm2 on 15mm than 20j/cm2 on 18mm? I just don’t get it.
You have a higher energy because…
15mm spot size is 7.5^2 * 3.14= 176 mm^2 or 1.76cm^2.
1.76 * 35 = 61.6J…Which is more energy than ~50 (what you get at 18mm and 20J). The energy per area is higher even if the area you are working with is smaller.
While it’s true that the laser spot size gives you more penetration at a given fluence, I’m guessing that the energy of the beam also contributes in part to the depth that a laser will go through a medium. After all, the beam of a stronger flash light travels much farther in darkness than the beam of a weaker one.
So, if you were comparing 50J to 60J, I’d guess the 60J would ultimately dig deeper (not prepared to answer this scientifically; it’s only a guess). But, again, none of this matters. 60J may well be over the tolerable limit of skin and simply just burn people. I have no idea. 35J is not an available setting at that spot size on the gentlelase. There’s probably a reason–since I’ve read that the GentleLase actually has a maximum output of 100J.
This has some of the specifications listed:
http://www.bogomoletsclinic.com.ua/en/?view=txt&div=en_news&id=54114290204
Don’t know how reliable of a source it is.
You have a higher energy because…
15mm spot size is 7.5^2 * 3.14= 176 mm^2 or 1.76cm^2.
1.76 * 35 = 61.6J…Which is more energy than ~50 (what you get at 18mm and 20J). The energy per area is higher even if the area you are working with is smaller.
You got me wrong, I understand 35J/cm2 on 15mm gives us more energy mathematically. What I am asking is, why are you trying to find more total energy on a smaller spot size with more maximum fluence? It may be more or less. It is just the engineer’s decision who designed the system.
The energy per area is higher even if the area you are working with is smaller.
Of course it is and you don’t have to do any calculation to find that out as you did. The energy per area is actually the fluence and simply 35 J/cm2 > 20 J/cm2.
So, if you were comparing 50J to 60J, I’d guess the 60J would ultimately dig deeper (not prepared to answer this scientifically; it’s only a guess). But, again, none of this matters. 60J may well be over the tolerable limit of skin and simply just burn people. I have no idea. 35J is not an available setting at that spot size on the gentlelase. There’s probably a reason–since I’ve read that the GentleLase actually has a maximum output of 100J.
Actually we should define what deeper penetration is? Laser beam is made of photons and on average each photon penetrates down to the same distance regardless of fluence. Read my post above with the ESS definition. I tried to explain it.
So, if you were comparing 50J to 60J, I’d guess the 60J would ultimately dig deeper
First, you have to talk in terms of fluences, not total energies if you are trying to make comparison. Anyway, if we assume we have 20 J/cm2 at both 15mm and 18mm, by your analogy they should penetrate at the same depth. Think of photons as particles having probability distributions of passing through a follicle. The maximum penetration depth that a single photon can have is the same on two spots. Now, let us forget about this for the moment and concentrate on chances of seeing a photon on a follicle. It is clear that we would have a total number of 3.24N photons and 2.25N photons for 18mm and 15mm spot sizes, respectively. So, a follicle under the skin surface spot that laser beam hits on has better chance to be struck by more number of photons on 18mm. This is simply because we have much more photons. This means we definitely see more photons at the follicle site at 18mm. More photons means more energy, better chance of achieving higher temperature, better chance of being burned up. This is what is meant by deeper penetration. Or think it this way, let’s say a photon can penetrate as much as 5mm through the skin. At 18mm you would have more number of photons reaching the maximum depth of 5mm. There is no such thing as 18mm max penetrates 6mm through the skin, and 15mm can only penetrate max 4.5mm or so. They are all the same. The trick is the [color:#CC0000]number of photons[/color].
The reason is that I have seen people begin programs that start at 18mm spot size and 18-20J “progress” to 15mm spot size and 30J thinking that they were getting stronger treatment than they were before. I wanted to see if the difference in energy would warrant such a claim.
I don’t know what the motives are behind these programs. It may have something to do with design of the laser machines. I mean the capability of a laser machine may slightly differ at different spot sizes. There is also this pulse duration parameter which may be effecting effectiveness and may have a different range at varying spot sizes. Another thing is according to spot size, fluence, pulse duration and etc, ESS (effective spot) I mentioned before does not have a uniform change as we go deeper in the skin. Careful analysis may reveal different spot sizes used in different treatments may actually contribute to better reduction. Also, after each laser treatment your hair structure and topography chances, so it may be more suitable to use a different size spot.
Finally, the effectiveness of treatment is closely related to the overlapping technique used. This is often overlooked and I tried to bring it into discussion at http://www.hairtell.com/forum/ubbthreads.php/topics/54922/Bringing_up_overlapping.html#Post54922 . However, it didn’t attract much attention.
Also, keep in mind that settings are different for different types of machines, so when you look at the studies etc, you cannot compare diode to alexandrite to Yag settings. Only alex to alex, diode to diode, etc.