Christmas lighting technology has been subject to considerable development and variation since the replacement of candles by electric lights.
Incandescent light bulbs

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

 have been commonly used in Christmas lights until recently. These lights produce a broad-spectrum white light, and are colored by coating the glass envelope with a transparent or translucent paint which acts as a color filter

Filter (optics)

Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....

. Some early Japanese-made lamps, however, used colored glass.