Slit series {collimator}| make light passing through have only one direction.
Computer monitors or television screens have a smallest element {pixel}|. Elements can have different intensities.
Arc lamps can illuminate transparent film slides {projector}|. Light goes through magnifying lenses to focus on screen. A glass plate absorbs hot infrared-light rays before they reach film. Slides have a glass slide holder to prevent warping by heat. Fan cools projector.
Light {actinic light}| can have optimum spectra for photosynthesis. It is for aquariums with plants or coral.
Electric arcs emit light {arc lamp}|.
Electric current passed through a tube heats mercury vapor slightly to emit ultraviolet light {fluorescent light}|. Ultraviolet light hits tube phosphorescent coating, to give white light. Fluorescent light is more efficient and cooler than incandescent light. Fluorescent light has more light at different wavelengths.
Light bulbs {incandescent bulb}| send electric current through tungsten filaments, which become white-hot. Bulb is globe of clear or frosted glass, with vacuum or nitrogen gas inside. If filament breaks, bulb burns out. You can hear filament hitting glass if you shake bulb.
Lamps {photoflood}| can have high intensity and one direction.
Light {strobe light}| {stroboscope} can flash on and off faster than 30 times per second. Photographs can show stopped action clearly.
Strings {wick} can have paraffin wax or beeswax coverings {candle, burning}|. Flame heat melts wax, which string soaks up. Wax then vaporizes and burns.
thin candle {taper}.
Electronic number displays can use transistors that emit red light when charged {light emitting diode}| (LED).
Electronic number displays {nixie tube}| can use gas discharge around cathodes.
Organic molecule diodes {organic light-emitting device}| (OLED) can emit colored light with electric current.
Crystals {photonic crystal}| can have empty spaces in refractive substances. It prevents a wavelength band {photonic band gap} from passing, by refraction and reflection. If substance is polymer and empty spaces are liquid crystals that can move around, affected wavelengths can change. Frequency can change, light passage can delay, or wavelength range can narrow. If liquid-crystal orientations are random, light scatters. If orientations align, material is transparent. Diffraction grating is one-dimensional photonic crystal.
Electronic number displays can use cathodes on flat bases {planar gas discharge}|.
Kerosene lamps {hurricane lamp}| can have shields to prevent extinguishing by wind.
alcohol or kerosene lamp {spirit lamp}|.
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Date Modified: 2022.0225