Times Square, Las Vegas, Picadilly Circus, the local liquor store or coffee shop--would any of these be the same without bright glowing neon signs? Part of neon's attraction is the appearance of changing colors.

Neon lights don't actually change colors. Neon signs give the illusion of changing color by turning different components of the signs on or off.

This is probably the most fun demonstration you forgot from science class. Tubes of glass are filled with different gases (not plain air). When the sealed tubes get zapped with electricity, they glow. Argon, krypton, xenon, and radon are the other noble gases used besides neon and each glows differently. By tinting the tubing, even more colors can be created.

Light-emitting diodes (LEDs) are gradually replacing neon signs on the commercial market because they can be used to create more complicated displays and are energy efficient.

Neon signage isn't just for the commercial world anymore and is being used more and more as a medium for art and sculptures.

Anyone who plans to work with any of these gases should learn how to use them safely. For example, radon is radioactive and believed to cause lung cancer. Most of the gases are odorless and colorless at room temperature and will kill you if a tank leak occurs without proper ventilation.