Now that you can calculate what dose you are getting, you need to know what dose is actually effective. Most review articles and educational material tends to claim a dose in the range of 0.1J/cm² to 6J/cm² is optimal for cells, with less doing nothing and much more cancelling out the benefits.
However, some studies find positive results in much higher ranges, such as 20J/cm², 70J/cm², and even as high as 700J/cm². It’s possible that a deeper systemic effect is seen at the higher doses, depending on how much energy is applied in total to the body. It could also be that the higher dose is effective because the light penetrates deeper. Getting a dose of 1J/cm² in the top layer of skin will only take seconds. Getting a dose of 1J/cm² in deep muscle tissue could take 1000 times as long, requiring 1000J/cm²+ on the skin above.
Distance of the light source is crucially important here, as it determines the light power density hitting the skin. For example, using the Red Light Device at 25cm instead of 10cm would increase the application time required but cover a larger area of skin. There’s nothing wrong with using it from further away, just be sure to compensate by increasing application time.
Calculating how long a session
Now you should know your light’s power density (varying by distance) and the dose you want. Use the formula below to calculate how many seconds you need to apply your light for:
Time = Dose ÷ (Power density x 0.001)
Time in seconds, dose in J/cm² and power density in mW/cm²