Visible light has no significant effect when it shines on us. But other types of light, like X-rays and gamma rays, are much more powerful.
With the shortest wavelengths, X-rays and gamma rays are found at the far end of the electromagnetic spectrum.
They have much higher frequencies than other light waves and therefore carry more energy.
They can travel great distances through air, and although dense materials like lead can reduce their intensity significantly, these rays can pass easily through the human body.
And it is here where they can cause serious harm.
The danger lies in their ability to dislocate electrons from atoms and molecules when they come into contact with them, in a process called ionization.
Ionization can damage or even destroy living cells.
But it is precisely these properties that make X-rays and gamma rays extremely useful in medical practice, when used in controlled circumstances.
X-rays, which pass through tissue, but not bone, are used to produce detailed internal images of the human body, and are now essential in medical diagnosis.
Gamma rays have the smallest wavelengths, and the most energy of the electromagnetic spectrum.
Their ionizing power is used in the treatment of cancerous tumors.
The gamma rays are directed onto the tumor from different angles.
Because they are concentrated only at the targeted area, gamma rays can destroy harmful cells without damaging surrounding tissue.
Hospital workers use shielding to limit their exposure to X-rays and gamma rays.
These protect them from the deadly rays that are vital to saving their patients.