The Sun
Light is made of energy waves, with different wavelengths being perceived by the human eye as different colours. The sun, our strongest source of light and the basis for life on Earth, contains all of the wavelengths listed below. But as you've just read, this makes the sun a "double edged sword"; it both heals and harms us.
Another problem with the sun is that modern society requires us to wear clothes. This means even when we go outside most of our body never gets exposed to the red and near-infrared wavelengths contained in the sun.