Holiday lighting technology has been subject to considerable development and variation since the replacement of candles by electric lights. While originally used during the Christmas holidays as Christmas lights, modern electric light arrays have become popular around the world in many cultures and are used both during religious festivals and for other purposes unconnected to any festivities.
Incandescent lights
Incandescent light bulbs have been commonly used in holiday lights until recently. These lights produce a broad-spectrum white light, and are colored by coating the glass envelope with a translucent paint which acts as a color filter. Some early Japanese-made lamps used colored glass.
Glow discharge lights Glow discharge light bulbs also can be used as holiday lights. The most common are neon, argon and mercury fluorescent lamps. They can glow in different colors, depending on the gas filling or the chemical composition of the phosphor. Neon lamps have a characteristic orange color, argon glow purple. Mercury lamps have most of the spectrum in the UV range, so their inner part of the bulb is covered with a phosphor, which converts invisible UV radiation into blue, green, yellow or other-colored light.
LEDs
Light-emitting diode (LED) holiday lights are quickly gaining popularity in many places due to their low energy usage, long lifetime, and associated low maintenance. Colored LEDs are far more efficient at producing light than their colored incandescent counterparts.
There are two types of LEDs: colored LEDs and white LEDs. Colored LEDs emit a specific color light (monochromatic light), regardless of the color of the transparent plastic lens that encases the LED's chip. The plastic may be colored for cosmetic reasons, but does not substantially affect the color of the light emitted. Holiday lights of this type do not suffer from color fading because the light is determined by the LED's chip rather than the plastic lens.
White LEDs are similar in most respects such as power and durability, but utilize a two-stage process to create the white (polychromatic, or broad spectrum) light. In the first stage, the LED produces one color of light, similar to any other LED. In the second stage, some of the blue or violet-blue is absorbed by a phosphor, which fluoresces yellow, imitating the broad spectrum of colors which the eye perceives as "white". This is essentially the same process used in fluorescent lamps, except for the use of an LED to create blue light rather than excited gas plasma to create ultraviolet.
White LEDs can be used as white holiday lights or to create any other color through the use of colored refractors and lenses similar to those used with incandescent bulbs. Color fading may occur due to the exposure of colored plastics to sunlight or heat, as with ordinary holiday lights. Yellowing may also occur in the epoxy body in which the LED is encased if left in the sun consistently.
LEDs use much less electricity (only 4 watts for a 70-light string) and have a much greater lifespan than incandescent lamps. Since they are constructed from solid state materials and have no metallic filaments to burn out or break, LEDs are much less susceptible to breakage from impact or rough handling.
Although LEDs are long-life devices, older or lower-quality strands of LED-based holiday lights can suffer from early failure. This is particularly so with blue ones, which are the newest and most expensive, and therefore prone to cost-cutting. Most LED-based holiday lights use copper wire which connects to the plated, copper-alloy leads of the LEDs. Having dissimilar metals in contact can result in galvanic corrosion inside of the lamps' sockets, causing them to stop working. Some older sets of LED holiday lights have each LED permanently mounted in a non-removable weathertight base to keep out moisture, helping to prevent such corrosion. However, this prevents the user from replacing defective lamps.
Many mini sets use standard 3 mm dome-shaped LEDs, and have a plastic cover over them to provide refraction, which is an important step in diffusing the unidirectional light they cast. These covers come in C5, C6, and C7 sizes (, , and -inch, or 16, 19, and 22 mm diameters, respectively) pointed "strawberries", G12 (12mm or almost -inch) globe "raspberries", and "M5" (5mm or -inch) pointed cylinders, equivalent to the T mini lights so common since the 1980s. For blue and green, these covers may have some fluorescence, leading to a lighter color. Other sets have 5 mm domes with no covers because these project light in one direction. Instead they have a cone-shaped indentation on the top to refract light out to the sides. Still other sets have covers like snowflakes (or for Halloween, pumpkins). There are also multi-LED screw-in bulbs which replace real C and C bulbs and are much closer in brightness than the mini imitations.
In the modern age, LEDs have emerged with RGB technology to allow Christmas lights to display a possible range of around 4.6 billion colors. One alternative is the use of RGBW technology which also adds the ability for lights to allow display a range of whites from warmer to cooler. RGB technology allows for far more animation than standard electronic light controls including the ability to smoothly fade through different colors.
One drawback to this technology for outdoor lighting, at least in North America, has been that squirrels have been found damaging them. The species must wear down their continually-growing incisors by gnawing on hard objects. They apparently find the diode's durable plastic construction useful for this, while its low power consumption means a minimal chance of electrical shocks to discourage them. Animal experts have suggested leaving edible hard nuts on the ground around lighting fixtures to distract the rodents with food that can serve the same dental needs.
Fiber optic lights Fiber optic technology is also used in holiday lighting, especially by incorporating it into artificial Christmas trees. Incandescent lamps or LEDs are located in the tree base and many optic fibers extend from the lamps to the ends of the tree branches.
Bubble lights Bubble lights are a type of incandescent novelty light that acquired some popularity during the 1950s. Their main feature is a sealed glass tube with a colored bubbling liquid inside, created by the heat from the incandescent light. The fluid within the vial was originally a lightweight oil, but now is methylene chloride for a more consistent bubble effect. While the idea was first demonstrated by Benjamin Franklin, the idea was adapted for use in Christmas lights. They were invented by Carl Otis in 1935, who sold the patents to the NOMA Electric Corporation. There is a long story involving patent fights. Bubble lights can still be purchased online and in stores to this day.
Laser projectors Laser projector systems became a prominent phenomenon in 2015; the devices are typically installed on a stake in front of a house, projecting colored dots resembling stars. The devices are marketed as being safer and easier to install than traditional string lights. The concept was popularized by Telebrands, which launched a brand of low-cost laser projectors known as Star Shower Laser Light in July 2015. Star Shower saw a considerably high demand, with stores quickly running out of stock, and reports of the devices being stolen right out of front yards; The New York Times compared the phenomenon to those of Teletubbies and Cabbage Patch Kids toys. In 2016, Star Shower introduced an updated version of their product with motion effects.
While the popularity of Star Shower and its imitators have been credited to their ease of use, laser projectors have received mixed reception from professional holiday lighting designers; one called them the "lazy way" to decorate a house, and another argued that "there's nothing more aesthetically pleasing and magical than a fully decorated house and landscape." Curbed also acknowledged that the devices can "throw a smattering of errant green measles upon your neighbor's garage. Or your parked car.", and that Star Shower had put out warnings stating that they were not to be used within 10 miles of an airport lest they interfere with pilots' vision.
Light sculptures
Lights are sometimes mounted on frames—typically metal for large lights and plastic for miniature ones. These were first used for public displays on lampposts, street lights, and telephone poles in cities and towns. For public displays large C7 bulbs are generally used, but by the 1990s light sculptures were being made in smaller form with miniature lights for home use. Consumer types now tend to come with a plastic sheet backing printed in the proper design, and in the 2000s now with nearly photographic quality graphics and usually on a holographic "laser" backing. Public displays often have outdoor-rated garland on the frame as well, making them very decorative even in the daytime. Places where notable displays of light sculptures may be seen include Gatlinburg and Pigeon Forge, Tennessee.
On a smaller scale, one of the most popular light sculptures is the sparkleball. Sparkleballs are handmade globes made from threading holiday lights into a sphere built of plastic cups. The cups are joined by soldering, cable ties, or with a hand stapler. Usually spotted individually on front porches at Christmas, the residents of North Yale Avenue in Fullerton, California have made a holiday tradition of hanging 450 sparkleballs from the trees lining their street.
Sizes Note that the following may be particular to North America, and may vary in countries with mains other than 120 volts.
Christmas lighting began with small C6 bulbs — where the C means "cone" for the candle flame shape and the 6 indicates the diameter measured in eighths of an inch, inches (19 mm). These were on a miniature candelabra screw-base, now designated E10 (Edison screw, 10 mm). Replicas of these bulbs are now produced as miniature strings, usually with the entire bulb replaced, but sometimes with a decorative cover with regular bulbs inside. These bulbs tend to be transparent white or colors, and are often ornately designed with crystal-like patterns.
Later bulbs called C, have diameters of seven and a half 1/8th inches ( in, or 24 mm) using an E12 candelabra base; however, these have a blunt shape (and should therefore be called B, or B24). Mixing metric and English units, there are also now G30 globes which are 30 mm ( in, or G) in diameter using these sockets. These are still used for the classic look or even retro style, and use about five watts each. Older bulbs drew watts of power, and were reduced to save power. Early bulbs, as well as some new antique reproductions, are made in various shapes and then painted like Christmas ornaments. Bubble lights and twinkle bulbs also come in this size.
Outdoor-only bulbs are designated C ( in, or 29 mm), and have a similar blunt shape as the C, but use an E17 "intermediate" base. Some modern versions of these strings are now listed for indoor and outdoor use. These bulbs are rated at about seven watts each, and are available in a globe shape, designated G40 (40 mm, or in). Some of the blunt-shape bulbs now come painted with designs, or swirled in more than one color. It is now very difficult to find twinkle bulbs in this size.