There are 4 different colors of LED bulbs. However, the infrared (IR) bulbs cannot be seen with the human eye, since they are outside of the visible spectrum, and will appear to be "off".
The IR bulbs penetrate deepest into the skin, since they are the longest wavelength. These bulbs help to heat deep into the dermis, causing new collagen and elastin, and are very beneficial for anti-aging. However, as we note in the user manual, these will appear "off" while they are indeed working, and they comprise 25% of the LED panel (spread throughout the panel).