I touched on the topic of dosing LLLT/PBM in a couple of other articles but it it might be a good idea write it up in a separate article. Light can be a tricky subject to get your head around but it is important when using these targeted devices to dose appropriately. While I don’t see it as a hugely risky treatment there is reason to be cautious. Too high or too low of a dose will lead to an ineffective treatment. There are some studies showing that it can be harmful, at least in certain issues like the thyroid. I’ve also seen plenty of people report problems with pain in their throat after using red or near-infrared light, usually at what seems like an inappropriate dose. I’ve covered some of those risks in articles before, here and here. This paper explains that too high of a dose is as ineffective as too low a dose.
So in this article I will look at the basic measurements that are used for light therapy. I’m going to focus on the main three factors and exclude pulsed devices to keep things simple(r). I’ll also look at some databases and show you how I would go about finding appropriate dose ranges. Light is not a one size fit all treatment. There are some very fundamental effects that red and near infrared light have on the mitochondria, and then there are many studies showing that different methods of application are required to address different problems. So let’s start by looking at some of the basic metrics:
Wavelength is the measurement of the distance between one point on a light wave to the next similar point. We don’t really need to know a whole lot about this but we do need to pay attention to the wavelength numbers which are given in the studies. Low level light therapy generally uses light with a wavelength between 600 and 1100 nm(nanometers). It’s best to find a light source that is closest in terms of wavelength (nm) to the most effective wavelengths shown in the studies for that particular treatment. For example, when I was investigating the effects of light on thyroid I found that most of the work had been done using 830 nm. So if someone was to treat thyroid it seems best to find a device with that wavelength or very close to it. This is not to say that other wavelengths don’t work, only that most of the existing data suggest that 830 nm does work.
Power Or Energy Density
Next we need to find the right energy density. This is the amount of light energy that will reach the skin or target area. With deeper treatments the energy density will be relevant at the depth we are trying to treat, but usually the energy density is measured at the surface.
If you put a light sensor next to a 40 Watt bulb you will get a higher energy density reading than if you put a light sensor at the same distance from a 10W bulb. Power/energy density also depends on distance from the light source. So as you move the light sensor way from the light source the energy density reading will decrease. At a far enough distance the energy density from the 40 W bulb will become the same or less than the energy density close to the 10 W bulb. Energy density is dependent on the power of the light source and the distance from it to the target.
Energy intensity is measured in Watts or milliwatts. You need to find the appropriate energy density in milliwatts from the studies and use a light source that puts out that much energy density at the treatment surface, or you can use a light source that puts out a higher energy density and calculate the distance needed to bring you down to the required energy density.
There are a few things you can do. You can find a light source with that exact energy density required and place it on the skin/target. You can find a light source which lists the required energy density at a certain distance and then treat at that distance from the skin/target. You could use a light source that does not have a known energy density at any distance and then use a light meter to find out what distance from the skin gives you the correct energy density.
Energy density can be written and measured in a couple of ways. The first is the output from a narrow beam of light, usually a laser. This is written as milliwatts (mW). The second common way to report energy density is in milliwatts per centimetre squared (mW/cm2). This second measurement is usually used for wider light sources and incorporates an area measurement, giving an average measurement of the energy over that area. When using LEDs the measurement of mW/cm2 probably going to be more practical as LEDs generally have a wider beam and cover more area than a laser.
Total Energy Dose – Joules
The final element is the combination of energy density(power) and time. This is calculated by multiplying the energy density(in Watts by the time in seconds. One Joule is equal to 1 Watt for 1 second. There are 1000 mW in 1Watt, so once you know your energy density (mW) and your total dose (J) you can calculate the amount of seconds needed to achieve the appropriate dose in Joules.
For example: if we are to use an energy density of 50 mW/cm2 (50 milliwatts per centimeter squared) and we know that the total dose is 4J we will divide 4,000 by 50 giving us the irradiation time of 80 seconds.
In many studies they will give you the irradiation time for the treatment and you won’t have to make this calculation. Sometimes you may have a study that says to use 80 mW for a total dose of 4J, which would mean the time is 50 seconds. You may not know the right distance to achieve 80 mW, but you may know the distance to achieve 100 MW. In this case it’s probably worth trying 100 mW because it is reasonably close to what is given in the study (80mW). You can achieve the same dose in Joules by lowering the irradiation time. 80mW for 50s = 4J and 100mW for 40s =4J
Next let’s take a look at some of the sources for information on low level light therapy. The common databases for studies are Google Scholar and Pubmed. However, Vladimir Heiskanen has compiled a large database of low-level light therapy studies and this is probably the best place to start. You can check his website here and his Facebook group on the topic here.
The next question is what do you want to treat. Treatment parameters can vary enormously and so it is important to look to see if there is data for the condition you want to treat. For more information as to why you should not dose light without reading the studies I recommend reading about the biphasic dose response and my articles here and here.
To give an example I am going to look at rheumatoid arthritis. There are over a dozen studies on the topic in the database that I am using. Vladimir has colour-coded studies so I’ll select the ones which are in green. The sources have been hyperlinked in the link section on the right hand side of the database spreadsheet. So we can open these studies and see which ones are useful. You should also read the negative studies to see what the potential risks are.
Some of the studies will have enough relevant data in the abstract which is linked. Other studies may be accessed in their entirety by the link on the right-hand side of Pubmed. Sometimes the entire article is available for free and in some cases the relevant information may in the study but not in the abstract.
One of these studies shows positive results in humans, gives all the needed metrics, and is not pulsed (which requires different equipment).
This study – Low-power laser therapy in rheumatoid arthritis – showed that the treatment improved signs and symptoms of rheumatoid arthritis.
-“In the laser group the grip strength and finger flexibility improved, the swelling of the joints declined, the morning stiffness and pain decreased. The sedimentation rate and the number of leukocytes showed a fall with a significant trend.”
In the placebo group similar results were not reported. The abstract gives us two of the three dose measurements that we need
“3.58 J cm/2, continuous wave 820 nm”
Continuous wave means that the light was not pulsed on and off. By accessing the full study we can see that the dose time was given as 60 seconds. The device was a small laser and was applied separately for 60s each on each joint of the afflicted hand. With a wider beam LED you could illuminate all these joints at the same time.
From the information given we can calculate the power /energy density.
I’ll round 3.56J up to 3.6J
3.6J delivered over 60s.
1 Joule is 1 Watt over 1 second.
1 Watt is 1,000mW -> So I’m going to multiply 3.6 by 1,000 and divide by the time in seconds (60) to get the power density.
3,600/60=60 – Power/ energy density is about 60mW.
So to approximate this study we want a light source around 820 nm wavelength at 60mW for 60 seconds. There is probably some higher or lower range in all all those metrics that will work but the aim is to get as close as possible.
Red Light Man has some 830nm devices (probably close enough). You can see the data given for the larger 830nm device below. The mini device also produces enough energy for this purpose, though the larger device can cover a larger area at the same energy density.
The 830 device puts out 200mW/cm2 at 15cm from the surface of the device. It outputs 20mW/cm2 at 50cm. Both of these figures are a little too far from our target of 60mW/cm2. We know that light is subject to the inverse square law. This means that if we double the distance that the energy density will be one quarter at that distance.
So let’s double the distance of 15cm which we know gives us 200mW/cm.
15cm x2 = 30cm
When we double the distance the energy density must be divided by 4.
200mW/cm2 divided by 4 is 50mW/cm2 – which is in the range of what we’re looking for.
Dose is about 3.6J,
3600 divided by 50 is 72
We just need to measure 30cm from the surface of the light and apply light for 72 seconds to approximate this study. You can put a ruler or measuring tape on a table, measure the distance, place the hand there and use a stopwatch to time the treatment.
Another option would be to use the infrared camera illuminator type devices. These devices are a little further away in terms of wavelength at 850nm. These devices do not have energy density ratings so you must also get a light meter and test the output, which brings the cost up significantly. I have one of these 4LED type devices and tested it with my light meter. This device reads 60mW/cm2 at a distance of 5.5 inches, with the glass still in place. They emit more power when the glass cover is removed. This reading the same was before the camera flash, which is too fast to change the reading. The reading is 600W/m2 which is to be divided by 10 to give the result in mW/cm2.
I’ve tested a few of these type of device and found that similar looking devices give very different readings. The same casing can contain different parts. You should not assume that a similar device will give the same output. You should test these devices yourself if you’re going to use them. This particular device is very powerful if used at close range, too powerful to mess around with. Dosing at 5.5 inches from this device for 60 seconds would a give similar dose to that in the study (3.6J).
I hope this article was useful. If anything needs clarification you can contact me using the contact form on the homepage so I can improve the article.