How much electromagnetic energy can humans sense?

Our human eyes evolved to sense EM radiation in the visible light part of the spectrum as seeing in this range was critical to our survival (e.g seeing predators approaching, seeing and finding food, etc). We can also sense infrared part of the spectrum as heat, but we can't see IR with our eyes - although some technologies have been developed to do so.

We can't sense any wavelength higher than the color violet, which is why we can easily get sunburned by UV radiation that we can't sense and when you go for X-rays you feel nothing. We also can't sense EM energy lower that infrared. There is probably also a biological reason we can't sense radiation beyond UV. Radiation higher than UV is called ionizing, which means it can strip electrons from atoms and thereby breakup molecules. It would be difficult to evolve a "sense" that could detect radiation in this higher range when the radiation itself would be tearing the sensor apart! Fortunately, most of this higher energy stuff is filtered out by our atmosphere, but this becomes a real concern if you are an astronaut.

Other animals can sense different parts of the EM spectrum aside from the visible range. Some birds see in UV light and reptiles can sense IR radiation and they use this for hunting.