Laser Wavelengths Explained: 650 nm vs 678 nm for Hair Growth

Every device spec sheet quotes a wavelength in nanometres: iRestore about 650 nm, HairMax about 655 nm, Theradome about 678 nm. Here's what that number means and how much it should sway your choice.

What wavelength is

Wavelength sets the colour of the light and how it interacts with tissue. Visible red runs from roughly 620 to 750 nm. Shorter red wavelengths are absorbed more strongly near the surface; longer red and near-infrared wavelengths travel slightly deeper.

The "therapeutic window"

Research on photobiomodulation clusters in a window from about 630 to 680 nm for red light (and 800–900 nm for near-infrared). In this range the light is absorbed by cytochrome c oxidase in mitochondria — the proposed trigger for the cellular effects described in how laser hair therapy works. ADD CITATION

650 vs 678: does it matter?

Both sit inside the studied window, and both have cleared devices behind them. Hair follicles sit around 3–5 mm below the skin surface, and the difference in penetration between 650 and 678 nm at that depth is small. Brands sometimes market a longer wavelength as "deeper" — true in direction, but there's no strong head-to-head evidence that it produces better hair outcomes.

What matters more than the exact number

1. Total light delivered — the count and spread of light sources, and the session time
2. Coverage — whether the light reaches every thinning area
3. Consistency — sticking to the schedule for months

Our take

Treat wavelength as a pass/fail check — is it within roughly 630–680 nm? — then compare devices on light count, coverage and price. That's how we weight our rankings, and why iRestore leads despite not quoting the highest wavelength.