In this universe there are many thing that we cannot explain. Among these many things is light. Light, as far as we know, come in different wavelengths and the size of the wavelength determine what type of light it is. The middle wavelength lights are what gives us the seven basic colors of red, orange, yellow, green, blue, indigo and violet.
Beside these visible lights there are the lights that cannot be seen by the human eye. These invisible lights can be grouped into two other groups the long waves and short waves. The first group of waves is the longer wavelength of light including infrared and radio waves. Radio waves, the longest wavelengths, alternate and can be volatile. Arthur C.
Clarke said in the essay "The Light of Common Day" that since radio waves fluctuate so much no animal has ever been able to sense them. He goes on to say that if you had an eye big enough to see radio waves your eyes would be millions of times larger than a normal eye. The next longest wave is the infrared light waves. Infrared light is used nowadays to see in the night. Special goggles are designed to pick up infrared light making it possible to see at night. The next group of light waves are the shorter waves of ultraviolet and x-rays.
Ultraviolet light, sometimes referred to as UV, is right next to violet and is just beyond sight. UV light is what causes sunburns and can be very painful. In Arthur C. Clarks essay it states that even though UV light is not visible the retina of the human eye reacts powerfully to it.
He compare the human eye to a camera and says that a good camera need may types of lenses made out of different types of glass to take a good picture. The human eye has only one lens and cannot possible see UV light. The last type of light is the x-ray. The x-ray is the smallest wave and is used in the medical field greatly to take pictures through flesh of bones. Even though x-rays are very useful they ca be very dangerous. They have been know to disrupt radio waves and can poison a human body to the point of death.
In summary, the invisible lights can be broken down into large wavelength and short wavelength groups. The large wavelength group consists of radio waves and infrared light. Radio waves are sometimes volatile and infrared light is use to see at night among other things. The other set of invisible light, the short wavelength, include ultraviolet light and x-rays.
Ultraviolet light is not visible but affects the retina in the human eye. X-rays are helpful in hospitals but are lethal in large quantities.