Christmas Lighting Technology Has Been Subject to Considerable Development

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

Incandescent Christmas LightsIncandescent light bulbs 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 translucent paint which acts as a color filter. Some early Japanese-made lamps, however, used colored glass. While incandescent light sets are less expensive to purchase than similar LED sets, the operating cost is significantly more. The paint on the incandescent bulbs suffer from fading or flaking when exposed to weather. Older bulbs were also coated on the insides of the bulbs to prevent this effect, but were more costly to manufacture.

LEDs
(LED) Christmas lights are quickly gaining popularity in many places due to their low energy usage (about one tenth the energy used by incandescent bulbs), very long lifetimes, and associated low maintenance. Colored LEDs are also 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. Christmas 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. In addition, the plastic lens is much more durable than the glass envelope of incandescent bulbs.

White LEDs are similar to colored LEDs 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 actually only 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 our eyes perceive 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 Christmas 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 Christmas lights. Yellowing may also occur in the epoxy "bulb" 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 also much less susceptible to breakage from impact or rough handling.

Although LEDs themselves are long-life devices, older or lower-quality strands of LED-based Christmas 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; in addition, spares are rarely included with sets. Most LED-based Christmas lights use copper wire which connects to the aluminum-based wires of the LEDs. Exposing this combination of metals to moisture can result in galvanic corrosion inside of the lamps' sockets, causing them to stop working. Many other sets use cheaper steel leads on the LEDs, which instead rust, leading to the same result. Some older sets of LED Christmas lights have each LED permanently mounted in a non-removable weathertight base to keep out rain and other moisture, helping to prevent such corrosion; however, this prevents the user from replacing defective bulbs.

Most common consumer LED lamps produce intense, deep, pure colours, versus incandescent bulbs which generally have subtler, yellow-tinted colours, often somewhat faded especially if used outside. Blue tends to be the dimmest incandescent color, but the brightest in LED. While yellow is just the opposite. Very early strings of LED lights were noticeably dimmer than incandescent bulbs but now are often noticeably brighter. These factors combine to give LED lamps a distinct aesthetic from older incandescent strings, although white LEDs behind coloured lenses do offer the ability to provide a more incandescent-type appearance with most of the benefits of energy efficiency. In contrast, coloured-chip type LEDs produce intense colours. The negative aesthetics are largely due to the maturity of coloured LED versus newer white LED technology. As the technology improves so will the ability to change the aesthetics of the lamps at lower cost than at present. In 2007, "warm white" LED sets (having a color similar to that of a compact fluorescent light) became commonly available for the first time in U.S. stores. This color however would need to have more of an orange tint to match the color of very small incandescent bulbs because they burn at a lower temperature. Still, this provides a much closer match to incandescent light color than was available when only very cool (bluish) white was available. One can choose cool-white LEDs for their crisp or snow-white quality or warm white LEDs for their more familiar incandescent-like color.

Additionally, low-end sets do not contain power supplies (or have only a transformer instead of a SELV), and so the bulbs flicker in sync with the alternating current, being completely off when the voltage is negative. This produces a noticeable stroboscopic effect when an individual happens to move the lights across his or her field of view quickly, as when moving the eyes or turning the head rapidly. Higher-quality strings include a bridge rectifier to supply full-wave direct current to the lamps, making the lights brighter and greatly reducing the flickering (though there is still a small amount because diodes need a minimum voltage to begin conducting). Cheaper sets with two circuits connect each in the opposite polarity, which minimizes flicker in the combined light reflected from walls and also keeps power consumption symmetrical so as not to affect the electrical system.

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 (⅝, ¾, and ⅞-inch, or 16, 19, and 22 mm diameters, respectively) pointed "strawberries," G12 (12mm or almost ½-inch) globe "raspberries," and "M5" (5mm or 7⁄32-inch) pointed cylinders, equivalent to the T1¾ 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 C7½ and C9¼ bulbs and are much closer in brightness than the mini imitations.

One drawback discovered 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 need, 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 also serve the same dental needs.

Fiber optic lights
Fiber optic technology is also used in Christmas 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. These devices frequently use a step-down transformer because they have only one or two lamps or LEDs.

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.