Editing Fluorescent lamp (section)

==Phosphors and the spectrum of emitted light==
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[[File:Fluorescent lamp spectrum.jpg|thumb|Light from a fluorescent tube lamp reflected by a [[CD]] shows the individual bands of color.]]

The spectrum of light emitted from a fluorescent lamp is the combination of light directly emitted by the mercury vapor, and light emitted by the phosphorescent coating. The [[spectral line]]s from the mercury emission and the phosphorescence effect give a combined spectral distribution of light that is different from those produced by incandescent sources. The relative intensity of light emitted in each narrow band of wavelengths over the visible spectrum is in different proportions compared to that of an incandescent source. Colored objects are perceived differently under light sources with differing spectral distributions. For example, some people find the color rendition produced by some fluorescent lamps to be harsh and displeasing. A healthy person can sometimes appear to have an unhealthy skin tone under fluorescent lighting. The extent to which this phenomenon occurs is related to the light's spectral composition, and may be gauged by its [[color rendering index]] (CRI).

===Color temperature===
{{Main|Color temperature}}
[[File:Kelvin Temperature Chart.svg|thumb|The [[color temperature]] of different electric lamps]]
[[Correlated color temperature]] (CCT) is a measure of the "shade" of whiteness of a light source compared with a blackbody. Typical incandescent lighting is 2700 K, which is yellowish-white.<ref>{{Cite book|url=https://books.google.com/books?id=3nBhzo-bQWsC&q=Typical+incandescent+lighting+is+2700+K%2C+which+is+yellowish-white&pg=PT66|title=Lighting Design Basics|last1=Karlen|first1=Mark|last2=Benya|first2=James R.|last3=Spangler|first3=Christina|date=2012-06-01|publisher=John Wiley & Sons|isbn=9781118287927|language=en|access-date=2020-10-17 |archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420064855/https://books.google.com/books?id=3nBhzo-bQWsC&q=Typical+incandescent+lighting+is+2700+K%2C+which+is+yellowish-white&pg=PT66|url-status=live}}</ref> Halogen lighting is 3000 K.<ref>{{Cite book|url=https://books.google.com/books?id=mThZDgAAQBAJ&q=%C2%A0Halogen+lighting+is+3000+K&pg=PT71|title=Practical Lighting Design with LEDs|last1=Lenk|first1=Ron|last2=Lenk|first2=Carol|date=2017|publisher=John Wiley & Sons|isbn=9781119165323|language=en|access-date=2020-10-17 |archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420064855/https://books.google.com/books?id=mThZDgAAQBAJ&q=%C2%A0Halogen+lighting+is+3000+K&pg=PT71|url-status=live}}</ref> Fluorescent lamps are manufactured to a chosen CCT by altering the mixture of phosphors inside the tube. Warm-white fluorescents have CCT of 2700 K and are popular for residential lighting. Neutral-white fluorescents have a CCT of 3000 K or 3500 K. Cool-white fluorescents have a CCT of 4100 K and are popular for office lighting. Daylight fluorescents have a CCT of 6500 K, which is bluish-white.

===Color rendering index===
[[File:Helical fluorescent lamp spectrum by diffraction grating.JPG|thumb|A helical cool-white fluorescent lamp reflected in a [[diffraction grating]] reveals the various [[spectral lines]] which make up the light.]]
[[File:Various lighting spectrums - Flurescent incandescent diode and candle.jpg|thumb|Fluorescent spectra in comparison with other forms of lighting. Clockwise from upper left: Fluorescent lamp, [[incandescent bulb]], [[candle]] flame and [[LED lighting]].]]
{{Main|Color rendering index}}
Color rendering index (CRI) is an attempt to measure the ability of a light source to reveal the colors of various objects faithfully in comparison to a black body radiator. 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.{{r|GE1978|p=8}}

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.

===Phosphor composition===
{{Unreferenced section|date=May 2024}}
Some of the least pleasant light comes from tubes containing the older, [[calcium halophosphate]] [[phosphor]]s (chemical formula [[calcium|Ca]]<sub>5</sub>([[phosphorus|P]][[oxygen|O]]<sub>4</sub>)<sub>3</sub>([[fluorine|F]], [[chlorine|Cl]]):[[antimony|Sb]]<sup>3+</sup>, [[manganese|Mn]]<sup>2+</sup>). This phosphor mainly emits yellow and blue light, and relatively little green and red. In the absence of a reference, this mixture appears white to the eye, but the light has an incomplete [[spectrum]]. The [[color rendering index]] (CRI) of such lamps is around 60.

Since the 1990s, higher-quality fluorescent lamps use a [[Rare-earth element|rare-earth]] tri-phosphors mixture, based on [[europium]] and [[terbium]] ions, which have emission bands more evenly distributed over the spectrum of visible light, but with peaks in the red, green and blue. Triphosphor tubes give a more natural color reproduction to the human eye. The CRI of such lamps is typically 85.

{| class="wikitable"
|+ Fluorescent-lamp spectra
|-
| Typical fluorescent lamp with [[rare-earth]] phosphor || [[File:Fluorescent lighting spectrum peaks labeled with colored peaks added.png|frameless]] || A typical "cool white" fluorescent lamp utilizing two rare-earth-doped phosphors, [[terbium|Tb]]<sup>3+</sup>, [[cerium|Ce]]<sup>3+</sup>:[[lanthanum|La]]PO<sub>4</sub> for green and blue emission and [[europium|Eu]]:[[yttrium|Y]]<sub>2</sub>O<sub>3</sub> for red. For an explanation of the origin of the individual peaks click on the image. Several of the spectral peaks are directly generated from the mercury arc. This is likely the most common type of fluorescent lamp in use today.
|-
| An older-style halophosphate-phosphor fluorescent lamp || [[File:Spectrum of halophosphate type fluorescent bulb (f30t12 ww rs).png|frameless]] || Halophosphate phosphors in these lamps usually consist of trivalent [[antimony]]- and divalent [[manganese]]-doped [[calcium]] halophosphate (Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>([[chlorine|Cl]], [[fluorine|F]]):Sb<sup>3+</sup>, Mn<sup>2+</sup>). The color of the light output can be adjusted by altering the ratio of the blue-emitting antimony dopant and orange-emitting manganese dopant. The color rendering ability of these older-style lamps is quite poor. Halophosphate phosphors were invented by A. H. McKeag ''et al.'' in 1942.
|-
| "Natural sunshine" fluorescent light || [[File:Spectra-Philips 32T8 natural sunshine fluorescent light.svg|frameless]] || Peaks with stars are [[mercury (element)|mercury]] lines.
|-
| Yellow fluorescent lights || [[File:Yellow fluorescent light spectrum.png|frameless]] || The spectrum is nearly identical to a normal fluorescent lamp except for a near total lack of light shorter than 500 nanometers. This effect can be achieved through either specialized phosphor use or more commonly by the use of a simple yellow light filter. These lamps are commonly used as lighting for [[photolithography]] work in [[cleanrooms]] and as "bug repellent" outdoor lighting (the efficacy of which is questionable).
|-
| Spectrum of a "[[blacklight]]" lamp || [[Image:Fluorescent Black-Light spectrum with peaks labelled.gif|frameless]] || There is typically only one phosphor present in a blacklight lamp, usually consisting of [[europium]]-doped [[strontium]] [[borate|fluoroborate]], which is contained in an envelope of [[Wood's glass]].
|}