So what Dosage - How long should I treat myself?

Red light therapy has been gaining popularity in recent years as a natural and non-invasive way to improve various health issues, such as pain relief, wound healing, skin rejuvenation, and more. However, with the increasing popularity of red light therapy, there has been a lot of confusion surrounding the correct dosage. In this article, we will take a closer look at red light therapy and how to determine the correct dosage to achieve the best results.

What is Red Light Therapy?

Red light therapy is a form of low-level light therapy that uses red and near-infrared light to improve the health of cells and tissues. The light is absorbed by the cells and triggers a biological response, stimulating the production of ATP (adenosine triphosphate) which provides the energy for cells to function properly.

How Does Red Light Therapy Work?

Red light therapy works by penetrating the skin and reaching the underlying tissues, where it activates photoreceptors within the cells. This activation triggers the release of nitric oxide, a molecule that helps to dilate blood vessels and improve blood flow. The increased blood flow brings more oxygen and nutrients to the cells, which can help to reduce inflammation, improve healing and tissue regeneration, and reduce the appearance of fine lines and wrinkles.

What is the Correct Dosage for Red Light Therapy?

The correct dosage for red light therapy can vary depending on several factors, such as the type of device being used, the area being treated, and the individual’s health condition. Red light therapy is considered safe and non-invasive, and there have been no reported side effects from using it in the recommended dosages.

For best results, it is recommended to start with a low dosage and gradually increase the amount of time spent under the light as the body adjusts. Most red light therapy devices come with a recommended dosage, and it is best to follow the manufacturer’s instructions.

It is also important to keep in mind that red light therapy is not a cure-all and results may vary from person to person. However results are normally seen after several treatments. And it is important to be patient and consistent with the therapy.

How to Determine the Correct Dosage for Your Needs

To determine the correct dosage for your needs, it is always important to consult with a healthcare professional. They can help to assess your individual health condition and recommend a personalised treatment plan.

It is also important to pay attention to your body’s reaction to the therapy. If you experience any side effects, it is best to stop the therapy and consult with a healthcare professional.

Dosage is the term for the irradiation time. Too little light and it is insufficient to generate a true beneficial physiological effect. However, because RLT is biphasic, it means that too much light is not necessarily beneficial either. This is despite what you may have been told or read on some light therapy suppliers websites. What happens with an ever-increasing light dosage, is that the beneficial physiological effects peak, then degrade. See illustration below representing Arndt-Schultz Law as an example.

What is the Sweetspot with Red Light Therapy Dosage ?

A certain level of energy is required to obtain such effects, but over a given limit, the energy can be less than ideal. Whilst under a lower limit it has been demonstrated that the biological effects were minimal. Therefore it is best practice to keep the dosage within the therapeutic window referred to as the “sweet spot” region.

Arndt-Schulz curve

The sweet spot is usually between 6–100 joules per square centimetre (6 J/cm² — 100 J/cm²), as this “sweet spot” can vary depending upon the body part and the treatment. For example for wound care healing doses up to 10 J/cm² stimulate the wound healing rate whereas beyond that dose rates are inhibitory.

If you read a clinical study on RLT, it will often describe the dosage in Joules per square centimetre. The effectiveness depends on many treatment parameters.2,3,4,5. These include wavelength, depth of penetration, size of dose, time of application, level of power density, pulse repetition rate, and treatment protocol. To use the information we first need to know what is a joule?

What’s a Joule?

Joules are the standard of measurement for Light Therapy (i.e.Photobiomodulation).

Some scientists describe a Joule as a “Watt-Second”. One joule is equal to one watt/second. If you shine 1W of light on a surface for 1 second, you illuminated the surface with 1 joule of power.

If that one watt of light is falling on a square centimetre of space for one second, the energy delivered to that square centimetre is one joule per square centimetre (1J/cm²)

When working with RLT, the dose is usually around ten Joules per square centimetre (10J/cm²).

Red Light Therapy Unit Specifications

Most Red Light Therapy units will provide not only the wattage of the unit but more importantly the light intensity values at various distances away from the unit.

For example below is the Biocell 60 by Leredd

The LEDs have a 300 Watt rating. However, the unit only consumes 110 Watts of power. This RLT unit has a high light output illustrated in graphs, available on their website. It provides light in both 660nm and 850nm wavelengths of light.


This unit provides the power output in mW/cm² at various distances from the device. The power output from the device below is the combined light output for the RED 660nm and the NIR 850nm. It has has a sleek integrated module where you can turn on or off each wavelength of light or you can use the remote control which is an optional purchase. The total light output of the device is below. Importantly, the irradiance was measured by a Spectroradiometer for accuracy as opposed to solar meters which are commonly used to falsify and elevate irradiance levels.

Simplifying this, if you used a solar meter, the Strength numbers stated could be close to quadruple the reality. So it is important to know what method of measurement the supplier used to output their results as there is a massive difference so to compare apples v apples one should be diligent before drawing any comparisons. Some suppliers won’t even state what testing machine they used. It is possible that they don’t even know – which is a real red flag !


Red and NIR Light Therapy Dosage

Using the graphic above makes it relatively easy to calculate your dosage. At 15cm away from the unit, the power level is 100mW/cm². So each second at this level is delivering 100mW/cm². To obtain a 1J dosage you would need an exposure time of 10 seconds. Therefore in 1 minute you would be receiving a dosage of 6 Joules.

10 * 100mW/cm² = 1,000mW/cm²

1,000mW = 1Watt = 1Joule.

To obtain a 10-joule exposure would require 100 seconds i.e: Under 2 mins

Now let’s move further back to 90cm away from the light. The light will cover a greater portion of your body at a power density level of 14mW/cm².

How long of an exposure do you need for 10J ? (10J = 10,000mW/cm²)

10,000 / 14 = 714 seconds.

Divide 714 by 60 to convert seconds to minutes, 714/60 = 11.9

11.9 minutes will therefore give you 10 Joules

Simple Formula

This formula is a little quicker and performs the same function as the example above.

So re-doing our sample calculation from above 10J exposure using a radiance of 14 mW/cm² works out like this:

Answer = 11.9 minutes (same as before)

But this calculator takes all of the effort out of it and simplifies everything for you

  • Give your own a try – key in the details below into our Smart Dosage Calculator

Overdosing on RLT?

You may be concerned that you may be absorbing too much light energy from your Red Light Therapy. So now let’s compare the RLT energy of treatment to the energy the body receives in sunbathing.

The Energy in Joules From One Hour of Sunbathing

Here’s an interesting fact for you to consider. Approximately 42% of sunlight is Red and NIR light! Consequently, sunlight is approximately 88 mW/cm^2 in intensity, and thus we can estimate direct sunlight emits 37mW/cm^2 in the Red to NIR range.

Direct Solar Irradiance Chart

An adult human body has approximately 1.5 to 2.0 square metres of skin and that Two square metres works out to be 20,000 square centimetres.

The power density of sunlight is approximately 1 kilowatt per square metre at the Earth’s surface and this works out to be about 100mW/cm².

So taking that further, if you were out sunbathing for an hour (1 hour each side, front and back) you would be exposing your body to:
* 20,000 cm² X 100 mW/cm² = 2,000,000 mW or 2,000 Joules per second
* 2,000 Joules per second X 60 = 120,000 Joules per minute
* 120,000 Joules per minute X 60 = 7,200,000 Joules per hour.

The total energy dose to the body is 7,200,000 Joules.

To see that energy per cm² divide 7,200,000 by 20,000 = 360 Joules/cm²

Energy From Red Light Therapy

In comparison to sunbathing, in Red Light Therapy, we generally tend to limit our exposure to around 10 Joules/cm² per session

The Dosage will vary with treatment.

For any one anatomical area, the lower dosages are more effective for stimulating and accelerating healing and higher dosages will provide more pain relief.

Brain: Some brain research uses a 3,000 Joule dosage with power levels ranging from 10, 20, and 30 Joules per square centimetre.

Face Masks: Sold and used for anti-aging effects on the skin. If the face surface area of skin is approximately 500cm² and we provide a dosage of 10 Joules/cm² : delivers a total of 5000 Joules to the face.

Full Body Exposure:  Even a modest power density of 15 mW/cm² from a full body light panel can deliver a healthy dose of energy in a short time. Again:
* 20,000 cm² (skin surface area) x 15 mW/cm² (power density) equals 300,000 mW or 300 Joules per second
* 300 Joules/second x 60 = 18,000 Joules/minute
If you lay under a full body light panel for 5 minutes:
* 5 x 18,000 = 90,000 total Joules of energy.

If we divide by 20,000 (skin surface area) we arrive at 4.5J/cm²

So to achieve a healthy dose of 10-20 Joules per session based on the example and irradiance of 15 mW/cm² you would have a recommended treatment time of say 1020 minutes to reach the “Special Sweet Spot” zone. (SSS)

Most Can End Reading The Article Here!

Most people reading this article can end reading it here. As long as you have the critical light intensity information for your particular RLT unit, calculating your dosage and exposure time is relatively easy, as shown above.

But suppose you were purchasing an RLT unit without that critical information. In that case, you are going to need to use a little more maths or have access to a Spectroradiometer so please read on….

Red Light Therapy Power Density

The power density is the output power of the device, divided by the area of the device. Many devices have a higher wattage rating than their light energy output.

For instance, an RLT unit rated at 300 watts, may only output 100 watts of light energy. The reasons are this. Manufacturers typically sell a device based on the power levels of the individual LEDs that make up the unit. Assume there are 100 LEDs with each LED outputting 3 watts. 100 LEDs each rated at 3 watts = 300 watts.

LEDs are rarely driven at their maximum power rating. To increase the lifetime of the LED, they may only be driven at 33% of their rated power. For example: 0.33 multiplied by 300W = 99 Watts. Let’s round that off to 100 watts to make calculations easier.

So assume we have a 100-watt light output from an RLT device whose LED surface area is 30cm x 30cm. What is the power density?

First, we need to find the total area, that’s simple enough, 30 cm x 30 cm equals 900 cm². Now that we have our area calculated we can divide our power output into the area for our power density.

100 watts / 900cm² = 0.111watt/cm²

The term 0.111 watt is a little awkward, so we typically use the term milliwatts (a milliwatt is 1/1000 watt). So 0.111 watt = 111 milliwatts or 111mW. The power density of this light is 111mW/cm², at the surface of the device. Let’s rewrite our equation for clarity.

100 watts / 900cm² = 111mW/cm²

In most cases, you will be at a distance from the surface of your RLT unit. The light energy dissipates with distance as the light energy disperses to a larger area.

Measure The Light Intensity

The most accurate way to know the light intensity from a Light therapy unit is to measure the intensity using a Spectroradiometer as pictured that can measure the light at the wavelengths needed.


They are quite expensive and If you cannot obtain a Spectroradiometer you maybe able to rent or borrow one. Leredd also maybe able to procure one for you so suggest you make contact with them directly at co*****@le****.com

PAR meters are another option but often will not measure the NIR wavelengths which limit take measurements from the light source at measured intervals, like 15cm/6″, 30cm/12″, 45cm/ 18″ and 90cm/36″. This will be the most accurate light intensity measurement.

Estimate Light Intensity

The best estimates will be from the RLT unit manufacturer who ought to be providing light power density levels at predetermined distances from the unit.

More Information on Red Light Therapy and Photobiomodulation


Universal Dosage Calculator for Red Light Therapy! Find your optimal time per session!

The science of Red Light Therapy still has some grey areas in terms of how to properly dose the light! We are trying to make it more simple here but It is even more confusing by companies using inaccurate solar power meters, promoting high irradiances, and not always reporting the same units of intensity. And even the clinical studies report a wide range of dosages and intensities. Solar meters should not be used as their results are up to 4 x’s the true output which is grossly misleading.

Let’s say you have a light panel with 3rd party testing and you read a study that says a dose of about 6 J/cm² is ideal. So how do you calculate the distance and time it takes to get this dose?

You can do the maths here, but that seems daunting for most:

Time (seconds) = [Dose (J/cm^2) x 1000 (mW/W)] / Irradiance (mW/cm^2)

Now, you can just type-in the dose and irradiance for your light into our smart calculator, and it will tell you how long to use it for! The best part is that it works for ANY light-therapy light, as long as you have the accurate 3rd party irradiance measurements.


The “default” numbers above are actually for a Leredd Biocell 60 at 90cm with irradiance of 14 mW/cm^2, and a desired dose of 10 J/cm^2. We see the time it takes to achieve that dose is 11.9 minutes – so just a tad under 12 minutes.

I found that my ideal daily dose is between 6 J/cm^2 to 10 J/cm^2 for general wellness. If you are spacing your doses out every other day, or just a few times a week, then you could increase the dose higher as needed.

And it wouldn’t be a wrap unless we covered Joules Per Centimetre Squared Per Minute?

In the never-ending efforts for companies to cover-up their false intensity claims, they may tell you to ignore intensity entirely and base your dosing calculations on the “J/cm^² per minute.” That is simply convenient for them.

The J/cm^2 per minute is a metric sometimes called “fluence” in the studies because it describes both energy and time together.

This is actually a nice convenience, because if you know you want a 10 J/cm^2 dose and a company tells you their fluence is 2.5 J/cm^2 per minute, then the maths is a simple division. You know you need only 4 minutes to achieve that dose (minus any reflection losses if you are standing 15cm away).

But we know that the “J/cm^2 per minute” actually is easily converted to intensity of mW/cm^2 through the magic of simple maths.

  • 1 Joule/Second = 1 Watt
  • 1000 mW = 1 W
  • 1 minute = 60 seconds

We also know that when someone tells us the Joules/cm^2 per minute, that is a quick conversion equation.

  • mW/cm^2 = J/cm^2 per min * 1000 ÷ 60

For example:

  • 2.5 * 1000 ÷ 60 = 41.67 mW/cm^2

Thats it! Easy conversion from J/cm^2 per min back to mW/cm^2, the industry standard measurement. To make it easier, we’ve put it into another calculator. Give it a try !



Red light therapy has been shown to have numerous health benefits, and determining the correct dosage is an important part of achieving the best results. Whether you are looking to improve skin health, reduce pain, or boost athletic performance, it is important to consult with a healthcare professional and follow the manufacturer’s recommended dosages for best results.

Also remember that it is a common fallacy that “more power” means “faster treatments“. It has been shown that due to the biphasic dose response, that the Law of Reciprocity does not always apply to light therapy. That a “faster dose” does not always mean the same effectiveness, although it might appear to save a busy person some time.


The content and information contained in this article are for informational and educational purposes only. Information provided in this article is not and must not be taken as an alternative to any advice by a doctor, physician, or medical professional. It is not intended to provide medical advice or treatment. Safety of red light therapy, LLLT, Red or NIR light, and Photobiomodulation must always be reviewed by your doctor before beginning any treatment.

The author has narrated his research experiences in this article by observing and evaluating latest facts and figures. Reliance on the provided information has been done in good faith. The author cannot guarantee the validity and accuracy of the sources, which may change, be modified, updated, or removed in the future.

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