If buying a red light therapy device were like buying other health and wellness items, you’d ask, “What is the best wattage for red light therapy?” and you’d be done.

It’s not that easy with light therapy.

For most devices, you need to understand **red light therapy irradiance.**

But I’ll show you a shortcut to make it easy.

## Takeaways

**Watts **measures how much energy a red light therapy device uses per second. It’s not the output of light; it’s the input of energy that creates that light. A 5-watt light bulb uses 5 watts per second.

**Irradiance **measures how much light reaches a defined area over a defined time. In red light therapy, we usually speak of irradiance as how much light reaches a square centimeter per second.

**Joules **is a unit of energy. The irradiance measures how many **joules **have reached the target.

**Fluence **measures joules over the session span.

Most red light therapy companies define their device’s light output regarding **irradiance**.

**The larger the irradiance, the shorter the session time needed for a light dose.**

Almost all red light therapy manufacturers **overstate irradiance.**

This makes their devices appear to be more powerful than they are.

This makes the session times calculated from their irradiance values too short to get a good light dose.

**Mito Red Light states the fluence of their devices.**

They promise that the fluence is certified by a certified lab.

**We can use fluence to calculate an accurate session length.**

## Red Light Therapy Irradiance

I write huge articles explaining red light therapy because it’s just not obvious how to get a proper dose of light. Incorrect dosage leads to treatment failure.

**Irradiance is a huge problem in red light therapy shopping. **

**Manufacturers’ irradiance values cannot be trusted because many vendors use the wrong meter type to measure light delivery. **

**Mito Red Light now gives us fluence, a solid way to measure a device’s power.**

### Goldilocks Specifications

While calculating treatment time using irradiance is cum**bersome, it’s amazing** how easy it is to estimate treatment time using **fluence**.

### Use Joules or Irradiance, But Not Watts

Comparing **wattage** matters when buying a refrigerator or other appliance, but it’s useless when comparing **red light therapy devices.**

Watts tells you how much energy the device pulls to make its magic.

It doesn’t tell you how much light you receive.

**Irradiance** is the rate at which the light delivers photons **from a given distance** per **second**.

**The device’s wattage doesn’t tell us the irradiance.**

We need that from the vendor who measured light output using a proper **meter**.

#### Irradiance is Not Above Reproach

We usually use **irradiance **to calculate treatment time.

Once one vendor inflated their irradiance values, others did too so as **not to seem weak by comparison.**

Inflated irradiance values lead to vastly **understated treatment times**, which in turn lead to underdoses, which in turn lead to **failures**.

By publishing **fluence**, Mito Red Light gives us a **valid value to calculate treatment time.**

Use irradiance when you have a valid value. Use fluence when you can get this value.

**Below, you’ll learn how to calculate treatment time using irradiance or fluence.**

#### How to Calculate Dose Using Irradiance

**You can use this guide to calculate your treatment time per session if you have a reliable irradiance value.**

I will show you how in this section.

**However.**

These instructions are here for the absolute red light therapy geek.

**I encourage anyone who has a life to buy from a vendor that publishes certified fluence values, and then you can skip this section.**

You need a *reliable* irradiance value for any of this to make sense.

Are you sure you don’t want to skip this section?

Are you still here?

Let’s talk about calculating treatment time given a reliable irradiance value.

Let’s say a red light therapy device delivers **50 milliwatts per square centimeter per second,** which we write as **50 mW/cm2**.

**That irradiance is incomplete. **It delivers 50 milliwatts from what **distance**?

An irradiance value is meaningless unless we know how far away the light is from the target.

For this example, we’ll pick 6 inches as the distance.

The proper way to state the device’s irradiance is now:

**50 mW/cm2 per second at 6 inches**

Everything you need to know about dosage is in that statement:

**We will use this data to calculate session time for a target dose.**

You can always skip this and read the easy fluence instructions.

Don’t say I didn’t offer you an out.

##### Step 1: Convert Irradiance to One Minute

The irradiance per second is too short to get a meaningful treatment time, so we will convert it from **one second to one minute**.

**To get irradiance per minute, multiply irradiance by 60 seconds:**

(50 mW/cm^2 per second @ 6 inches **x** 60 seconds per minute) = **3,000 mW/cm^2 per minute @ 6 inches**

Our new irradiance delivers the same energy, but per minute: 3,000 mW/cm^2 at 6 inches per minute.

##### Step 2: Derive Joules (Fluence) from Irradiance

Now we know that **3,000 milliwatts of photons are moving to the sq. cm. spot per minute.**

That’s the **delivery rate**, but **how many photons** did we deliver?

We need to know how many photons we deliver to make a dose.

**According to science, the best dosage is between 5 and 60 joules.**

To convert from milliwatts to watts, divide the irradiance by 1,000.

**3,000 mW/cm^2 at 6 inches per minute / 1,000 milliwatts per watt = 3 joules per minute**

Are you still with me? We’re done.

**We now know that 50 mW/cm^2 at our arbitrary-for-the-sake-of-example distance of 6 inches per second works out to 3 joules per minute at 6 inches.**

##### Step 3: Derive Minutes per Session

Now, we can calculate how **many minutes of treatment **it takes to get our target joules.

Let’s say you want to go for a **5-joules dose.**

How many sets of **3 joules** do you need to get **5 joules?**

**Divide the target joules by the joules per minute to get the treatment time.**

- 5 joules target dose / 3 joules per minute = 1.67 minutes treatment time
- What is .67 of a minute?
- .67 of a minute x 60 seconds per minute = 40 seconds

**The treatment time is 1 minute 40 seconds from 6 inches to deliver 5 joules.**

##### Summary of Treatment Time Steps

**Irradiance per second:**50 mW/cm^2 at 6 inches

**Irradiance per minute:**50 mW/cm^2 at 6 inches x 60 seconds per minute = 3,000 mW/cm^2 per minute at 6 inches

**Joules:**3000 mW/cm^2 per minute at 6 inches/ 1,000 to convert milliwatts to watts =**3 joules per minute**at 6 inches

**Joules Target Dose:**5J

**Treatment Time:**5 joules target / 3 joules per minute at 6 inches = 1.67 minutes

**.67 of a minute**in seconds is .67 x 60 = 40.2 seconds*Treat for 1 minute 40 seconds at 6 inches to get 5 joules.*

Now throw that all out and use fluence to calculate treatment time.

#### Why Fluence Eats Irradiance for Breakfast

To start with a confession, Mito Red Light Therapy uses **the same meter as their competitors** to state **irradiance**.

If they use the wrong meter, **don’t they severely overstate irradiance?**

Yes, they do and say as much on their product pages.

On their product pages, Mito Red Light advises customers **not to use irradiance to calculate dosing.**

Here is **the fluence**, they say. Use this certified value that is **not inflated** to calculate treatment time.

I understand why Mito Red Light includes inflated irradiance values.

They do it for the same reason almost all other vendors do it.

**The average consumer would not understand the nuance that it’s taking me 3,000 words to explain to you.**

The average consumer would never read an article like the one you’re reading.

**The average consumer sees 50 mW and 150 mW and assumes that 150 mW is better. **

**End of story. **

**The average consumer buys 150 mW because it must be big, strong, and powerful.**

Session time is inversely related to irradiance.

A **very large irradiance** has a **smaller session time.**

Inflated** irradiance** has an **abnormally short session** time that might not deliver enough photons to make any difference.

But Mito Red Light also publishes product-certified **fluence** values for dosing.** **

**And just like that, dosing becomes easy, honest, and effective.**

**Fluence is all we need**.

Now, it is **crazy easy** to calculate treatment time.

#### How to Calculate Treatment Time Using Fluence

First, to calculate treatment time using fluence, decide on target joules for the entire session.

For deep muscle recovery and pain relief, we will target 60 joules.

Divide the desired joules

**Desired joules per session:** 60

**Device fluence: **3.4 joules/cm2/minute

**Treatment time: **Desired joules divided by fluence = treatment time in minutes

60 / 3.4 = 17.6 minutes

Mito Red Light is the only vendor I know about using fluence certified by a third-party lab.

This gives us a dependable value for calculating light dose treatment times.

### Conclusion

**Fluence** is superior to irradiance when calculating red light therapy treatment times.

**Irradiance** is usually inflated.

**Vendors** should display fluence per minute (but not per cm. sq.) and explicitly state the **distance** at which that fluence value is relevant.