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}|.
7-Machine-Kinds-Illumination-Lighting
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Date Modified: 2022.0225