Green, Red, White or Blue Light Therapy?

by Laura Falls on 17 Apr 2015

What is light therapy?

Light therapy (or phototherapy) involves exposure to specific wavelengths of light for a prescribed amount of time at a specific time of day.

Bright light therapy has been used to treat circadian rhythm disorders and Seasonal Affective Disorder (SAD) for more than a decade. According to Mayo Clinic, light therapy is the main form of treatment for Seasonal Affective Disorder.

Whilst light therapy as a treatment is highly regarded there is still a lot of new research and debate around the topic of “what light is most effective?”

Today, I’m going to narrow the research findings down as much as possible for you.

What is a wavelength?

Firstly, I’d like to explain what I mean when I refer to different wavelengths of light.

The diagram below shows all wavelengths of light.


What is visible light?

The visible wavelengths (the light we can see) are between 400 and 700 nanometers (nm). This is also known as white light. White light contains every colour of the rainbow.

What colors are more effective for adjusting the body clock?

The wavelengths in the left half side of the rainbow are the ‘shorter wavelengths of light’. Shorter wavelengths (i.e. green and blue light therapy) have been proven to be more effective at re-timing the body clock and suppressing melatonin. Melatonin is the hormone produced in our brain which causes us to feel sleepy. By altering melatonin levels using light we can change the time our body feels tired (and re-time the body clock!).

Those to the right (i.e. red) are useful for treating some skin conditions however are ineffective for adjusting the body clock.

As white includes all colors (including yellow and red) it is less effective than blue or green light on their own.

Are some colors of light safer for your eyes?

For eye safety, 100% UV-free light is recommended. The wavelengths to the left hand side of the rainbow are closer to Ultra Violet (UV) light.

There have been some concerns over long term exposure to blue light. Using wavelengths of blue light below 430nm increases the potential hazard (Grimm et al. 2001).

What about brightness or lux?

One other topic of debate around light therapy is the recommended lux. Lux is the measure of brightness at a specified distance. A light bulb will have a different lux if it is 20cm away from the eye compared to if it was 1m away. The ‘distance’ part often causes confusion.

A 1995 study showed that green light therapy at doses of 350 lux produced melatonin suppression and circadian shifts equivalent to 10,000 lux white light therapy (Ahmed et al. 1995).

Why was the Re-Timer light chosen?

The Re-Timer light is 506 lux on the high setting which is sufficient given the proximity to the wearers eye and the optimal angle in which the light is being delivered.

Re-Timer emits a blue-green color of light (500nm) and the device has been independently tested for eye safety to the international standard CEI IEC 62471.

This colour was selected following 25 years of University research and has been chosen for both safety and its effectiveness.

If you would like to learn more about light therapy, please visit our Light Therapy page.