If you’ve started exploring light therapy and infrared saunas, you’ve probably seen these terms thrown around a lot, sometimes interchangeably. They’re not the same thing, and understanding the difference helps you get more out of both your sauna and your red light panel.

The Basics: It’s All About Wavelength

Light exists on a spectrum, and most of it is invisible to the naked eye. The wavelength of light — measured in nanometers (nm) for shorter wavelengths, micrometers (μm) for longer ones — determines how deeply it penetrates tissue and what it does when it gets there. Different wavelengths have meaningfully different effects on the body.

Far Infrared (FIR)

Far infrared sits at the longer end of the infrared spectrum, typically in the range of 3 to 10 micrometers. This is the wavelength range your sauna’s wall, back, and calf heater panels operate in.

FIR energy is absorbed at the skin surface and experienced as deep, penetrating warmth. Unlike convection heat (hot air), far infrared heats the body directly, which is why an infrared sauna cabin can sit at a lower ambient temperature than a traditional sauna while still producing an intense and sustained sweat.

Near Infrared (NIR)

Near infrared sits between visible red light and far infrared, roughly 700 to 1400 nm. At this range, light is invisible but penetrates more deeply into tissue than red light — reaching muscle, joint, and even bone in the right conditions.

NIR is used in photobiomodulation therapy: exposing tissue to specific light wavelengths to support cellular energy production and recovery. It produces little heat compared to far infrared, which is why red light therapy panels (including ours) feel very different to sit in front of than sauna heater panels.

Red Light

Red light occupies the 630–700 nm range of the visible spectrum — you can see it as the deep red glow from a therapy panel. It penetrates less deeply than NIR but works on surface and shallow tissue, and is often paired with NIR in therapy panels to address different tissue depths simultaneously.

Like NIR, red light therapy works through photobiomodulation rather than heat.

Full Spectrum

“Full spectrum” typically refers to a light therapy device that combines multiple wavelengths — usually red light and near infrared, sometimes extending into the far infrared range as well. The idea is to deliver benefits across multiple tissue depths in a single session rather than targeting only one wavelength.

Side by Side

How They Work Together in Your Plunge Sauna

Your sauna delivers both types of therapy in a single session. The FIR heater panels in the walls, back wall, and calf area provide the radiant heat your body absorbs during a session. The red light panel, mounted on the glass door, delivers targeted photobiomodulation across seven wavelengths before, during, or after your heat session.

They work through different mechanisms and at different tissue depths, which is why using both together offers something neither does alone.