[This page is an extended version of the Dosing section of the Red Light Therapy Guide.  It covers in more detail what was not included in the Guide because of space considerations.]

All light devices only convert a percentage of the power they consume (input) as light, so it is not uncommon to see an LED panel with an input of 1000 watts produce an output of 300 watts. That’s because all devices convert less than 100% of their input to useful light (but they are still 3-4 times as efficient as incandescent lights).

So, to relate this to how much useful light the body receives from a device, the term we use is irradiance. Irradiance is the output power per unit area produced by a device, commonly stated in milliwatts per square centimeter (mW/cm2).


When working with RLT, we need to consider the dose, or how much light is necessary to produce healing effects. There is a formula for calculating dosage. (Don’t worry. Even if you didn’t like math, we’re going to break it all down quickly, then make it really simple to figure out how much light you need to heal.)

The formula for calculating proper dosing factors in the power of the device and the length of time you are exposed to the light.

dose = power density X time

Dosage for light therapy is expressed in units of energy. A unit of energy produced by RLT devices that most of us are familiar with is calories. In the metric system, the equivalent energy unit is joules. And since most scientific studies use the metric system, joules are the units we will use here.

The power density is a measure of the power of the device – measured in watts – and how close the light is to you. So power density is measured in milliwatts per square centimeter.

dose (joules) = power density (mW/cm2) X time (minutes)

Now, all of the explanation above was for the benefit those of you who were curious.

Thankfully, the whole issue of figuring out proper RLT dosage can be made much simpler.

For this, we turn to probably the foremost expert in RLT research, Dr. Michael R. Hamblin. Dr. Hamblin is a Principal Investigator at the Wellman Center for Photomedicine at Massachusetts General Hospital, is on the faculty of Harvard Medical School, directs a laboratory of a dozen scientists who work in light therapy and has published over 400 peer-reviewed articles and more than 10 major textbooks on light therapy. (His books were written at the level of his professional colleagues and are priced out of the reach of most non-professionals, but you can find a list of them here: )

Dr. Hamblin reduces the whole issue of measuring dosages of RLT (dosimetry) down to common sense:

Expose the part(s) of your body you want to heal to the light for 10-15 minutes, 1-2 times a day.

That’s it. Dr. Hamblin has stated in multiple interviews that, because of variations between people and their conditions, it is unnecessary to bother with precise formulas to calculate dosimetry. He has suggested that hard numbers or formulas are used in published RLT studies because it is customary, or standard procedure for scientific literature. And that makes a lot of sense because most medical research studies are focused on drugs which can be very dangerous or even lethal if proper dosages are not followed. So precision in drug dosages is very important for safety reasons.

Fortunately, that level of caution is not needed with RLT, because you can take comfort in knowing that, even though RLT is extremely powerful, RLT is also extremely safe. The most common side-effect recorded in studies is that one may experience a slower rate of healing if RLT is used for too short or too long a period of time.

So, less precision is simpler – yet perfectly safe. Time and again, Dr. Hamblin’s ‘rule of thumb’ has proven to cover virtually every use of RLT.

While it is understandable that some reading this will feel the need to have something more exact, light therapy changes all the rules. It is possibly the most fluid of all healing modalities – ever.

In some ways it seems like it might be easier to capture smoke in a bottle than to pin down exact numbers for the exact dosages for any particular health issue. For those who more exact guidelines, based on surveying many experts, as of this point, with a rapidly evolving technology:

For skin issues – 5-20 J/cm2 (joules/square centimeter)

For deeper tissues – 10-100 J/cm2

What does this mean in terms of the health issue you need to address? That depends on what device you are using. See the next section, pick a device, then your questions will be answered.

Power Density: Simply put, having a more powerful red light device gives you more options than a less powerful one. Power density is usually measured in milliwatts per square centimeter, written as mW/cm2. Generally, the range considered therapeutic – the level needed to actually see medical benefits – is about:

5-200 J/cm2 (joules/square centimeter)

That is:

5-20 J/cm2 for skin issues 3-15
10-200 J/cm2 for deeper tissues 10-40
120J total (15-20 min/day total)

Once you know this, you can choose the device that’s best for your needs.

Of course, red light power diminishes the further you are from the source.

There is a law of diminishing returns that kicks in at some point. Here it is in visual form (also known as the Arndt-Schulz Curve).

In plain English, the more therapeutic red light received by the body, the better (the rising curve), but only up to a point. Beyond that, the benefits begin to fall off to a point where you can undo those benefits and, if you continue long enough, you can even slow the rate of healing.

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