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 (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 -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. In the