What is a “Dose” of Red Light Therapy?

A dose of red light is a lot like a dose of sunshine. If you get too little, nothing happens. If you get enough, you trigger a healthy response. If you get too much, you can hurt yourself.

A dose of red light therapy is a quantity of energy measured in joules from light with a wavelength of 600 to 1200 nanometers.

Whether the dose we just defined is actually helpful to the body depends on:

  • the wavelength being the right one for the target treatment, and
  • the energy quantity being sufficient to kick off energy-creation and healing cascades of events

These parameters all affect how many joules of energy make it into the user:

  • the red light therapy device’s output power density
  • the distance the lamp is from the user (power density part 1)
  • the size of the treatment area (power density part 2)
  • the time the user spends in treatment
  • the frequency of treatment sessions


I am not a doctor. This is not medical device. You are responsible for what you do with this information.

Red Light Dose Terms

As you read this article, come back to these terms to deepen your understanding.

Wavelength is the Quality of the Light

  • Wavelength: Light travels in a wave. The distance from one wave peak to the next is a wavelength.
  • Nanometer: A nanometer (nm) is a billionth of a meter. Visible and infrared energy wavelengths are between 400 and 1200 billionths of a meter (nm) long.

Joules is the Quantity of the Light

  • Energy: energy is the ability to displace a mass over distance
  • Joules: A joule is a unit of energy.

Power is the Rate of Energy Transfer

  • Power: power is the rate at which energy is transferred
  • Watt (W): A watt is a measure of power.
  • Milliwatt (mw): A milliwatt is 1/1000th of a watt.

Therapeutic Red Light Dose

  • The wavelength: the light must be one of the red or infrared wavelengths
  • The joules: the body must absorb the light energy in sufficient quantity

Power Density over Time = Joules

  • Power Density: the power at a spot at a specific distance from the light
  • Treatment Time per sessions is measured in seconds
  • Joules = power density x treatment time

A Dose is Quantity and Quality of Light

A red light dose is a quantity of light energy of a specific quantity and wavelength.

A therapeutic dose of red light therapy is a quantity of red or infrared light that the body absorbs in some quantity sufficient to kick off healing cascades of events.

The Body Likes Certain Wavelengths

Healing wavelengths are in the 600 to 1200 nm range. Many but not all wavelengths in this range are therapeutic.

Some wavelengths appear to do nothing, or we just have not yet figured out what they do.

To date, no study has found that any of the red or infrared wavelengths used in red light therapy are harmful.

Consumer LED red light devices typically output two light wavelengths.

One is in the 600-700 nm range, and one is in the 800-900 nm range.

When we say “red light therapy,” we are referring to therapy using light in both the red and the infrared ranges.

It is just easier to say “red light” therapy than “red and infrared light” therapy.

Red Light Dose Examples

A typical red light therapy dose from an LED device is:

  • Between 1 and 50 joules
  • In the 630 to 850 nm wavelength range

If you were to dose yourself with one joule of a 635-nanometer wavelength light, the dose would be:

1 J of 635 nm

If you were to dose yourself with twenty joules of an 850-nanometer wavelength light, the dose would be:

20 J of 850 nm

How Powerful is Your RLT Device?

A red light therapy device is not 2 watts or 500 milliwatts.
Those are expressions of power, but they’re not specific enough to help you with your red light dose.

The only power that matters is the output power density.

The power density is an expression incorporating power, space, and distance, and looks like this:

mW/cm^2 at distance

For example, if you sit 12 inches from the device and receive 50 mW of energy right in the center of the light’s beam, then the power density is:

50 mW/cm^2 at 12 inches

How Distance Matters

If the light is 12 inches away and transfer 50 mW/cm^2 of energy, how much energy does it transfer when the light is 6 inches away? What if the light is 24 inches from you?

The power at 6 inches is not twice as much, and the power at 24 inches is not half as much.

Energy drops in intensity with distance, but not at a linear rate. Double distance does not equate to half the power. Half the distance does not equate to double the power.

How the Spot Matters

If you point a beam of light at your face, how much energy lands on your feet?

Light spreads outward with distance. The most energy goes to the focal point, directly from the center of the lamp.

Rather than measuring the ever widening and weakening energy intensity, we draw a one centimeter square directly across from the focal point.

The power is highest across from the focal point.

Pay the Troll with Joules

Joules (J) is a measure of photons received.

Healthy doses range from less than one joule more than 50 J.

The lamp outputs its energy at a rate in milliwatts (mW).

In our example, the lamp outputs 50 mW of energy that you can receive if you are 6 inches from the bulbs.

If you’re 3 inches from the bulbs, it will be more than 50 mW.

If you’re 9 inches from the bulbs, it will be less than 50 mW.

“50 mW at 6 inches” is the lamp’s irradiance.

The quantity of joules you will get is just the milliwatts multipled by the treatment time in seconds.

Because we’re in the milliwatts (thousandths of a watt), we have to then divide that by 1000

In one second, the lamp outputs 50 mW.

(1 second treatment x 50 mW)  / 1000 = 0.05 J

A 1 second treatment with a 50 mW irradiance gives you 5/10th of a joule.

What about one minute at 50 mW?

(60 seconds treatment x 50 mW) / 1000 = 3 J

A one minute treatment gives you 3 J.

Is 3 joules enough?

It depends.

Studies show that the healing response can occur at various joules.

This is why, if you don’t get a response from the lamp, you need to increase the time you spend with it.

The lamp’s power might be over promised. You might be 9 inches rather than 6 inches away from the bulbs.

Energy transfer drops off dramatically with distance.It’s easy to get too few joules.

When you first start treatment, the body will absorb the initial photons, but will not do anything with them.

The photon-absorbing cellular buckets will fill with photons, but the gate containing the healing response will stay closed.

When the buckets get a healing enough photons, the troll opens the gate, letting the heaing response out.

A small dose doesn’t have a small effect.

A small dose does nothing.

On the other hand, too much light reverses healing responses.

A light overdose is harmful.

Fortunately, it’s very hard to get too much light using an LED consumer device.

The knowledge we have of too much light comes from researchers using lasers rather than LEDs.

So if you’re not getting a healing response, you might not have given the troll enough joules.

Do longer treatments to give the troll its fee.

How to Use Power Density to Figure Treatment Time

If you have a target amount of joules for your treatment goal, you can use power density to figure out how long your session should be.

The formula for figuring treatment time is:

s = ( joules / power density ) x 1000

For example, you want to absorb 5 joules. The device’s power density is 50 mW/cm^2 at 6 inches, then:

s = ( 5 / 50 ) / 1000 = 100 seconds

How to Use Power Density to Compare two RLT Devices

The lamp with the greater power density gives the fastest treatment times.

Which lamp will give you a faster RLT session?

Which Lamp Gives the Fastest Red Light Treatment?
Light 1
Light 2
Input Power
5 W
6 W
Output Power
4 W
5 W
Output Power Density @ 6 inches
100 mW/cm^2
80 mW/cm^2

The input power and output power of Light 2 are higher than Lamp 1. The output power density of Lamp 1 is higher than Lamp 2. Dose for dose, Lamp 1 is faster.

How to Find Target Joules Doses

The EMF Channel free Light Dose Database (opens in new window) lets you search for wavelength-joule doses by treatment goal.

You can use the joules and wavelength study data to create your own treatment doses.

To copy the study dose, your device has to output light in the same wavelength range as that used in the study.

To give yourself that dose, you will need a light that emits wavelengths near the wavelength used in the study. The body responds to a range of wavelengths, so your device does not need offer the exact same light as that used in the study.

People Also Ask

If I know how many joules I want, the the power density of my device, how do I calculate treatment time per session? Use the free EMF Channel Treatment Time Calculator (opens in new window), or plug your joules and power density into this formula:

s = ( joules / power density ) x 1000

How do I use my device to copy someone else’s red light therapy dose? A dose is the joules and wavelength. Your device wavelength needs to be similar to the dose you’re copying. Use any device to get the joules. If your device is weaker, spend more time per session. If your device is stronger, spend less time per session. Read complete instructions here: How to Copy Any Red Light Therapy Dose with Your Device (opens on this site).
Photo by Pedro Figueras from Pexels

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