Light Colours & Wavelength
Light Colours & Wavelength Explained
A device might glow red blue or purple but what does that actually tell you?
Different wavelengths interact with tissue differently. Understanding those differences helps you look beyond the colour settings and understand what a device delivers.
What Is a Wavelength?
Wavelength describes a physical property of light. In light therapy, it is usually measured in nanometres, written as nm.
Numbers such as 415 nm, 633 nm, 660 nm and 850 nm identify different wavelengths. They do not describe the device’s power or tell you how effective it will be.
Visible wavelengths appear as different colours. Near-infrared light sits beyond the visible red part of the spectrum and is invisible to our eyes.
Colour tells us something about the light. The wavelength specification tells us more.
Red Light
Common examples: 630, 633 and 660 nm.
Red light is visible. It is widely studied in photobiomodulation, including research into skin appearance, tissue repair and other biological responses.
Some human studies using particular red-light protocols have reported improvements in skin texture and wrinkle measurements. These findings relate to the equipment and treatment conditions tested; they do not guarantee the same results from every red-light device.
Red light is often described as “surface light,” but that is an oversimplification. Some red light can travel beneath the skin’s surface. How much reaches a particular tissue depends on the wavelength, the tissue and the device’s output.
Near-Infrared Light
Common examples: 810, 830 and 850 nm.
Near-infrared light is invisible, so a near-infrared LED may appear unlit even when it is operating.
Selected near-infrared wavelengths generally travel through tissue more readily than shorter visible wavelengths. This is one reason they are used in research involving deeper tissues.
However, “penetrates deeper” does not mean that all the emitted light reaches a muscle or joint. Light is absorbed and scattered as it travels, and its intensity decreases.
There is no single penetration depth that applies to every person, body area or device.
Red vs Near-Infrared: What Is the Difference?
Red light is visible; near-infrared light is invisible.
Both are used in photobiomodulation research. Their wavelengths affect how light travels through tissue and which light-absorbing molecules it can interact with.
They are sometimes used together, but a combination is not automatically better. The relevant question is whether that combination, at the delivered dose, has been studied for the intended purpose.
Near-infrared also differs from the far-infrared technology commonly associated with infrared saunas. The term “infrared” covers a broad range of wavelengths; it does not identify one treatment or one biological effect.
This illustration draws on Bashkatov et al. (2005), who calculated optical penetration depths of approximately 1.8 mm at 660 nm and 2.4 mm at 850 nm from laboratory measurements of human skin. These values describe how light weakens within tissue, rather than where it stops or how deeply it produces treatment effects. The illustration is not to scale, and actual penetration varies with tissue characteristics and the light source.
Blue Light
Research examples include approximately 405–470 nm.
Blue light has been studied for acne, particularly inflammatory acne. One proposed mechanism involves light-sensitive compounds called porphyrins produced by Cutibacterium acnes, a bacterium associated with acne.
When these compounds absorb certain wavelengths, they can trigger reactions that affect the bacteria.
Human studies have tested blue light alone and combinations of blue and red light. Results depend on the treatment protocol, and light therapy does not address every cause or type of acne.
Blue light also deserves care when pigmentation is a concern. Experimental human research has shown that blue-violet light can produce persistent pigmentation in some skin types under the exposure conditions tested. This does not mean every blue-light device causes pigmentation, but it does mean blue light should not be assumed suitable for everyone.
Green Light
Device examples often fall around 520–550 nm.
Green light is marketed for concerns such as uneven skin tone and pigmentation. However, evidence supporting those claims for home LED devices is less established than the marketing can suggest.
A result from a laboratory experiment, or from a green laser used in a clinic, does not establish that a green LED setting will produce the same result.
Treat broad claims such as “removes pigmentation” cautiously. Look for human research using a comparable device and protocol.
Yellow or Amber Light
A commonly studied example is 590 nm.
Yellow and amber light have been investigated for skin redness and responses following cosmetic procedures.
For example, a small clinical study tested a 590 nm LED treatment for redness following fractional laser treatment. That is a specific clinical situation; it does not establish that every yellow-light device treats everyday redness or rosacea.
“Yellow” and “amber” are descriptive labels. Check the wavelength rather than relying on the colour name alone.
Purple, Cyan and White Settings
Some devices offer purple, cyan or white modes by combining different visible wavelengths.
For example, red and blue light used together may look purple. That does not necessarily mean the device emits a separate violet wavelength.
A combined colour setting is not automatically a distinct treatment, and more colour modes do not necessarily mean more proven benefits.
Ask which wavelengths are emitted in each mode and whether their output has been measured.
Does a Higher Nanometre Number Mean Better Light?
No. Nanometres describe wavelength, not treatment quality.
A longer wavelength is not automatically more powerful, safer or more effective. Different wavelengths have different absorption and scattering characteristics, and the appropriate choice depends on the intended application.
Wavelength is only one part of the picture. Irradiance, exposure time, treatment distance, coverage and the delivery method also matter.
Why We Avoid Fixed “Depth Charts”
You may see diagrams claiming that blue light reaches one exact depth, red light another, and near-infrared several centimetres.
These can illustrate a general concept, but they should not be treated as precise predictions for a particular device.
Tissue thickness, pigmentation, blood content, wavelength and measurement method can all affect the result. Detecting a small amount of light at a depth also does not establish that it delivers an effective treatment dose there.
Choosing by Evidence, Not Just Colour
Before choosing a device or colour setting, look for:
• The actual wavelengths in nanometres.
• Measured irradiance at the intended treatment distance.
• Research relevant to the intended use.
• Clear instructions and eye-protection guidance.
• An explanation of whether colour modes combine wavelengths.
A study using a laser, a clinic-based system or a different dose may not apply directly to a home LED device.
Explore Further
Our Red Light Therapy 101 page explains photobiomodulation and cellular responses.
Understanding Irradiance explains light output, distance and exposure.
Clinical Studies provides summaries of human research, including the methods, findings, limitations and original publication links.
This page provides general education. Follow your device’s instructions and seek professional advice if you have a light-sensitive condition, take medication that increases light sensitivity, or are unsure which settings are appropriate. Do not stare directly into LEDs; follow the manufacturer’s eye-protection requirements.