NIR light is invisible to the naked eye. Don't worry, though - both the red (660 nm) and NIR (850 nm) LEDs are powered by the same supply, so if there was ever an issue with the NIR LEDs, the red LEDs would be affected, too.

What is the difference between red and near-infrared light?

Red light has a wavelength between 600-700 nm and is visible to the human eye. NIR light runs from 700-1400 nm and is not visible to the human eye.
Both red and NIR have stimulating effects within your cells, but the major difference between them is the depth of tissue penetration:

• Red light is absorbed quicker by the outer tissues, leading to superficial benefits such as increased collagen production and wound healing.
• The NIR light penetrates deeper into your tissues and leads to benefits such as decreased joint pain and improved muscle recovery.