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Incandescence Light bulb has a wire filament (tungsten) that is heated to high temperatures by an electric current passing through it. Electric Discharge Fluorescent light bulb – filled with an inert gas (eg. Argon, krypton, neon, xenon) as well as mercury vapor. When an electric current is passed through, it causes the mercury atoms to emit UV light. The UV light is absorbed by the fluorescent materials that coat the tube and excites them, which makes them re-emit visible light. Neon light has glass tubes filled with a gas like neon, argon or krypton at low pressure. At both ends of the tube there are metal electrodes. When you apply an electric current, the gas ionizes and electrons flow through the gas. The electrons excite the gas’ atoms and cause them to emit light. Different gases emit different lights (neon = orange, argon = blue, krypton = pink, xenon = purple). Phosphorescence Phosphor chemicals are used and there are many different kinds with various brightness, colour and glowing time lengths. These chemicals store energy when exposed to light and they have to be exposed for a while. When they are exposed to light, they get energized and then radiate visible light after being energized by slowly releasing their stored energy over time. As they release the energy, they emit small amounts of light, making them appear to glow in the dark. Examples of common phosphors are zinc sulphide and strontium aluminate. Fluorescence Fluorescent light bulb – filled with an inert gas (eg. Argon, krypton, neon, xenon) as well as mercury vapor. When an electric current is passed through, it causes the mercury atoms to emit UV light. The UV light is absorbed by the fluorescent materials that coat the tube and excites them, which makes them re-emit visible light. Chemiluminescence Chemiluminescence makes objects glow in the dark because of a chemical energy. When certain chemicals are mixed in a chemical reaction, they produce energy that is released thereafter, creating a glow, as seen in fireflies and glow sticks. Bioluminescence A naturally occurring light source. Creatures like fireflies, anglerfishes and jellyfishes contain special chemicals within them that cause them to glow for biological reasons (eg. Attracting mates, courtship, attracting prey, protection, etc). In the anglerfish, the light is used to attract prey. The light is created by masses of bacteria living in its “fishing rod” in which the bacteria themselves are bioluminescent! Tribioluminescence When certain materials are broken apart, rubbed, scratched or crushed, chemical bonds within them are broken. This separates the electric charges between, giving off sparks of light. It is not fully understood however. Light Emitting Diodes (LEDs) A semiconductor is a substance (usually a solid chemical element or compound) that can conduct electricity under some conditions but not others – making it a good medium for control of electric currents. Examples of elements are silicon, germanium and silicon carbide. When an electric current is applied, electrons located in the semiconductor material constantly move and their movement illuminates the light bulbs. Different from other light bulbs because it produces way less heat and is more energy efficient. This is because the semiconductor chosen can limit the amount of energy that flows through them.