What Is a Joule?

When examining clinical studies on RLT, you'll often encounter dosage expressed in joules per square centimeter. But what exactly is a joule?

Joules serve as the standard measurement unit for red light therapy (Photobiomodulation). One joule equates to one watt-second. Therefore, if you illuminate a surface with one watt of light for one second, you've effectively delivered one joule of energy.

In the context of RLT, a dosage is generally around 10 joules per square centimeter (10J/cm²).

Specifications of Red Light Therapy Units

Most RLT devices provide not only their wattage but also the light intensity at various distances.

I have tested five different units from multiple manufacturers, and the one I prefer is shown below. Its LEDs are rated at 600 watts, but the unit consumes only 315 watts of power. This particular RLT device boasts high light output, as illustrated in its graphs available on Amazon, emitting light in both 660nm and 850nm wavelengths.

This unit offers power output in mW/cm² at various distances, combining the light output from both the RED 660nm and NIR 850nm wavelengths. Individual switches allow for the control of each light type, and the total output is depicted in the chart below.

Calculating Dosage

Using the graphic above simplifies dosage calculation. At a distance of 6 inches from the unit, the power level is approximately 108mW/cm², which can be rounded to 100mW/cm² for ease of calculation. Thus, each second at this intensity delivers 100mW/cm², meaning you would need 10 seconds to reach a dosage of 1J.

10 * 100mW/cm² = 1000mW/cm²

1000mW = 1Watt = 1Joule

For a 10-joule exposure, the required time would be 100 seconds.

Now, if you step back to 36 inches, the power density drops to 46mW/cm². To achieve a 10J dosage:

10,000 / 46 = 218 seconds

Converting that to minutes, 218/60 = 3.6 minutes.

Concerns About Overexposure to RLT

You might wonder if you are receiving too much light energy from your RLT sessions. Let’s compare RLT energy to that absorbed during sunbathing.

The Energy from One Hour of Sunbathing

An adult's skin covers approximately 1.5 to 2.0 square meters, equating to about 20,000 square centimeters. The power density of sunlight is roughly 1.0 kilowatt per square meter, translating to about 100 mW/cm².

If you sunbathe for an hour (30 minutes on each side), your body is exposed to:

20,000 cm² X 100 mW/cm² = 2,000,000 mW, or 2,000 Joules per second.

This results in:

2,000 Joules/second * 60 = 120,000 Joules/minute

120,000 Joules/minute * 60 = 7,200,000 Joules/hour

Thus, the energy dose per cm² is:

7,200,000 / 20,000 = 360 Joules/cm².

Energy from Red Light Therapy

In contrast, RLT typically limits exposure to about 10 Joules/cm², with variations depending on the treatment.

Brain studies may utilize dosages as high as 3000 Joules, with various power levels ranging from 10 to 30 Joules per square centimeter. Face masks designed for anti-aging often deliver a total of 5000 Joules to the skin, assuming a face area of about 500 cm² at 10 Joules/cm².

Full Body Exposure

Even a modest power density of 15 mW/cm² in a light bed can yield significant energy in a short time:

20,000 cm² (skin area) x 15 mW/cm² = 300,000 mW, or 300 Joules/second.

300 Joules/second x 60 = 18,000 Joules/minute.

If you spend 5 minutes in the light bed:

5 x 18,000 = 90,000 total Joules of energy.

Dividing by 20,000 gives us approximately 4.5 J/cm².

Most Can Stop Here!

At this point, most readers can conclude their research. As long as you have the necessary light intensity information for your specific RLT device, determining dosage and exposure time becomes straightforward.

However, if you're considering purchasing an RLT unit without that essential data, you may need to perform additional calculations or acquire a PAR meter.

Metric Measurements

Using metric measurements is advisable since most literature adheres to this standard. The centimeter (cm) is commonly used, with a conversion factor of 2.54 to switch between centimeters and inches.

Power Density

Power density is calculated by dividing the output power of the device by its area. Many devices may list a higher wattage than what they actually produce in light energy.

For example, an RLT unit rated at 300 watts might only generate 100 watts of light energy. This discrepancy arises because manufacturers often base ratings on individual LEDs, which are rarely operated at maximum capacity to enhance their lifespan.

Assuming a 100-watt output from an RLT device with a surface area of 30 cm x 30 cm:

First, calculate the area: 30 cm x 30 cm = 900 cm².

Next, compute the power density:

100 watts / 900 cm² = 0.111 watt/cm²

This is typically expressed in milliwatts, resulting in a power density of 111 mW/cm² at the device's surface.

Estimating Light Intensity

Light intensity diminishes with distance. Here’s a rough estimate using the hypothetical light source with a power density of 111 mW/cm² at the surface:

At 30 cm: 50 mW/cm²

At 60 cm: 33 mW/cm²

At 90 cm: 24 mW/cm²

The most accurate estimates will come from the manufacturer's specifications, which should detail power density levels at various distances.

Further Insights on Red Light Therapy and Photobiomodulation

For those seeking more in-depth knowledge, I've published a book titled "Living Younger Longer Using Red Light Therapy," available on Amazon and my website in various formats.

Disclaimer

The information in this article is for educational purposes and should not be interpreted as medical advice. The author, John Iovine, has shared his research and observations based on reliable sources, although he cannot guarantee their continued accuracy or validity.

The first video explores the complexities of determining the correct dosage for red light therapy, addressing whether this challenge is insurmountable or manageable.

The second video offers valuable tips on dosing and timing for optimal results with red light therapy, providing practical advice for users.