From sunrise to screen glow, different wavelengths of light send different signals to the body, influencing everything from collagen production and mitochondrial energy to sleep timing and vitamin D synthesis.
Understanding the light spectrum helps us make sense of trends such as red light therapy, infrared saunas and circadian health — and also clarifies the difference between UVA and UVB exposure.
Here’s a simple guide to what sits where on the spectrum, and why it matters.
Why light matters
Light is measured in nanometres (nm). The shorter the wavelength, the higher the energy.
At one end of the spectrum sits infrared. This is warming and often therapeutic. In the middle is visible light – the colours we see. At the shorter end lies ultraviolet light, which is powerful and biologically active.
Each type interacts differently with the body.
- Some penetrate deeply into tissues.
- Some affect skin cells.
- Some influence circadian rhythm and hormone timing.
Here’s an easy-to-reference table that explains how each interacts with our bodies:
| Light type | Wavelength range (nm) | Notes / Benefits |
| Far-infrared (IR-C) | 3000nm–1mm | Deep warmth, supports detox, circulation, muscle relaxation – found in FIR saunas |
| Mid-infrared (IR-B) | 1400–3000nm | Less penetration, more heat – used in some saunas and heat therapy |
| Near-infrared (IR-A) | 700–1400nm | Deep tissue penetration, mitochondrial support, cellular energy (ATP) production |
| Red light | ~620–700nm | Surface skin repair, collagen support, reduced inflammation |
| Green light | ~495–570nm | May support calm and migraine relief, emerging area of research |
| Blue light | ~450–495nm | Boosts alertness and mood, but can disrupt sleep if overexposed at night |
| Visible light | 400–700nm | Includes violet, blue, green, yellow, orange, red – essential for circadian rhythm |
| Ultraviolet A (UVA) | 315–400nm | Penetrates deeper into skin, supports nitric oxide release, contributes to tanning |
| Ultraviolet B (UVB) | 280–315nm | Stimulates vitamin D production. Can cause sunburn |
| Ultraviolet C (UVC) | 100–280nm | Germicidal, blocked by ozone layer, not naturally reaching Earth’s surface |
