What is red light therapy?

Red light therapy is a broad, everyday term for the use of red wavelengths of visible light on the skin or body. In a skincare context it almost always means light delivered by LEDs — light-emitting diodes — rather than lasers or sunlight.

It is a description of a technology, not a promise of an outcome. Two devices can both be described as red light therapy and differ enormously in the light they produce, how close they sit to the skin, and how long a session lasts.

Where the red comes from

Visible light spans roughly 400 to 700 nanometres (nm). Blue sits at the short end, red at the long end. Red light therapy generally refers to the region of roughly 600–700 nm, which is why the light looks a deep rose or crimson to the eye.

Many devices pair red light with near-infrared light, which sits just past the visible range. Near-infrared is largely invisible, so a device can be emitting it while appearing to be off or dim in that area.

What it is not

Red light therapy is not UV. LED skincare devices are not tanning devices and do not use ultraviolet wavelengths.

It is also not a heat treatment in the way an infrared sauna is. Some devices feel gently warm in use; that warmth is a by-product rather than the mechanism.

And it is not a medical treatment. Consumer LED beauty devices are cosmetic products. If you are dealing with a diagnosed skin condition, that is a conversation for a GP or dermatologist, not a shopping decision.

At-home devices versus professional treatments

Professional in-clinic systems are typically larger, more powerful and used under supervision for a set protocol. At-home devices are designed around a different trade-off: lower intensity, shorter or more frequent sessions, and a form factor you will actually use on a Tuesday night.

Neither is automatically 'better'. They are built for different contexts, and an honest brand should tell you which one a product is.

What to check before you buy

• The specific wavelengths the device emits, stated in nanometres.
• Whether near-infrared is included, and at what wavelength.
• The manufacturer's stated session length and frequency.
• Eye protection guidance and any contraindications.
• Warranty length and who honours it.
• Whether the seller publishes this information at all — vagueness is itself an answer.

Where confirmed, Ilumi London product pages show manufacturer-supplied technical specifications, so you can compare like for like rather than marketing language.