page_title: Fluorescent lamp
section_title: Color rendering index
hierarchical_section_title: Fluorescent lamp / Phosphors and the spectrum of emitted light / Color rendering index
caption_attribution_description: English: A helical fluorescent lamp, photographed on a reflection diffraction-grating. The grating separates the light into its different spectral lines, which reflect at different angles.
context_page_description: A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output.
  Fluorescent lamp fixtures are more costly than incandescent lamps because they require a ballast to regulate the current through the lamp, but the lower energy cost typically offsets the higher initial cost. Compact fluorescent lamps are now available in the same popular sizes as incandescents and are used as an energy-saving alternative in homes.
  Because they contain mercury, many fluorescent lamps are classified as hazardous waste.
context_section_description: Color rendering index (CRI) is a measure of how well colors can be perceived using light from a source, relative to light from a reference source such as daylight or a blackbody of the same color temperature. By definition, an incandescent lamp has a CRI of 100. Real-life fluorescent tubes achieve CRIs of anywhere from 50 to 98. Fluorescent lamps with low CRI have phosphors that emit too little red light. Skin appears less pink, and hence "unhealthy" compared with incandescent lighting. Colored objects appear muted. For example, a low CRI 6800 K halophosphate tube (an extreme example) will make reds appear dull red or even brown. Since the eye is relatively less efficient at detecting red light, an improvement in color rendering index, with increased energy in the red part of the spectrum, may reduce the overall luminous efficacy.
  Lighting arrangements use fluorescent tubes in an assortment of tints of white. Mixing tube types within fittings can improve the color reproduction of lower quality tubes.
caption: A helical cool-white fluorescent lamp reflected in a diffraction grating reveals the various spectral lines which make up the light.
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