Wi-Fi uses a frequency of 2.4Ghz. These are microwaves, down below infra-red on this diagram of the electromagnetic spectrum.
![](http://upload.wikimedia.org/wikipedia/commons/8/8a/Electromagnetic-Spectrum.png)
All of these different frequencies are radiation. Some are dangerous. Radiation on the high-frequency and short-wavelength end of the electromagnetic spectrum is called "ionising" — high frequency ultraviolet, X-rays, and gamma rays—are ionizing because photons at this end of the spectrum have high energy and can do a lot of damage. That's why we put sun cream on.
Visible light radiation has less energy, infra-red even less and microwaves and radio waves even less.
We wouldn't really worry about putting another light on. And yet microwaves have a lot less energy than visible light.