Fluorescent-lamp formats

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Fluorescent lamps in various embodiments

Since their introduction as a commercial product in 1939, many different types of fluorescent lamp have been introduced. Systematic nomenclature identifies mass-market lamps as to overall shape, power rating, length, color, and other electrical and illuminating characteristics.

Tube designations[edit]

In the United States and Canada, lamps are typically identified by a code such as FxxTyy, where F is for fluorescent, and the first number (xx) indicates either the power in watts for bi-pin lamps, length in inches for single-pin and high-output lamps, and for circular bulbs, the diameter of the circular bulb. The T indicates that the shape of the bulb is tubular, and the last number (yy) is the diameter in eighths of an inch (sometimes in millimeters, rounded up to the nearest millimeter). Typical diameters are T12 or T38 (1+12 in or 38 mm) for larger, often less efficient lamps, T8 or T26 (1 in or 25 mm) for smaller and often energy-saving lamps, and T5 or T16 (58 in or 16 mm) for very small lamps, which may even operate from a battery-powered device.

Fluorescent tube diameter designation comparison
Designation Tube diameter Extra
(in) (mm) Socket Notes
T2 14 approx. 7 WP4.5×8.5d
T4 12 12.7 G5 bi-pin Slim lamps. Power ratings and lengths not standardized (and not the same) between different manufacturers
T5 T16 58 15.9
  • G5 bi-pin
  • 2GX13 quad-pin
  • G10q quad-pin
  • Original 4–13 W miniature fluorescent range from 1950s or earlier.[1]
  • Two newer ranges, high-efficiency (HE) 14–35 W, and high-output (HO) 24–80 W, introduced in the 1990s.[2]
  • Panasonic's range of FHL fluorescent tubes in 18W, 27W, and 36W varieties for the Japanese market.
  • Circular fluorescent tubes.
  • Thorn/General Electric 2D fluorescent lamps and other similar lamps from various manufacturers.
T6 34 19.05
  • Fa8 single-pin
  • G10q quad-pin
  • Single-pin fluorescent lamps.
  • Thorn/General Electric 2D fluorescent lamps and other similar lamps from various manufacturers.
T8 T26 1 25.4
  • G13 bi-pin
  • Fa8 single-pin
  • R17d recessed double contact
One of the first diameters of fluorescent lamps, with the 15W T8 and 30W T8 having been introduced in 1938.[3] The European energy-saving krypton T8 lamps were introduced by Thorn EMI during the 1970s.[4] The North American energy-saving argon T8 lamps weren't introduced until the 1980s.[5]
T9 T29 1+18 28.6
  • G10q quad-pin
  • G13 bi-pin
  • Circular fluorescent tubes
  • Some linear tubes
T10 1+14 31.75
  • G13 bi-pin
  • G10q quad-pin
  • High-lumen retrofit lamps for 40W T12 lamps in North America.
  • Popular tube diameter in Japan
  • Circular 32W and 40W T10 lamps (Older versions of the 32W and 40W T9 lamps)
T12 T38 1+12 38.1
  • G13 bi-pin
  • Fa8 single-pin
  • R17d recessed double contact
One of the first diameters of fluorescent lamps, with the 15W T12 and 20W T12 having been introduced in 1938. These aren't as efficient as newer lamp options.[6]
T17 2+18 54 G20 Mogul bi-pin Large size for 90W T17 (preheat) and 40W T17 (instant start)
PG17 2+18 54 R17d Recessed double contact General Electric's Power Groove tubes

For T2–T12 and T17, the number indicates the tube diameter in 18 inches, e.g. T2 → 28 in and T17 → 178 in. Whereas for T16 and T26–T38, the number indicates the approximate tube diameter in millimeters.


Cross section of a typical fluorescent lamp with and without a reflector

Some lamps have an internal opaque reflector. Coverage of the reflector ranges from 120° to 310° of the lamp's circumference.

Reflector lamps are used when light is only desired to be emitted in a single direction, or when an application requires the maximum amount of light. For example, these lamps can be used in tanning beds or in backlighting electronic displays. An internal reflector is more efficient than standard external reflectors. Another example is color matched aperture lights (with about 30° of opening) used in the food industry for robotic quality control inspection of cooked goods.

Aperture lamps have a clear break in the phosphor coating, typically of 30°, to concentrate light in one direction and provide higher brightness in the beam than can be achieved by uniform phosphor coatings. Aperture lamps include reflectors over the non-aperture area. Aperture lamps were commonly used in photocopiers in the 1960s and 1970s where a bank of fixed tubes was arranged to light up the image to be copied, but are rarely found nowadays. Aperture lamps can produce a concentrated beam of light suitable for edge-lit signs.

Single-pin lamps[edit]

Single-pin lamps (Also generically called "Slimline" in the United States) operate on an instant start ballast in the United States and Canada or on a series choke without a starter in 220-240V countries.

High-output/very high output lamps[edit]

High-output lamps are brighter and are driven at a higher electric current. They have a recessed double contact (R17d) base on each end, rather than a standard bi-pin base, which prevents them from being installed into the wrong fixture. Since about the early to mid-1950s to today, General Electric has developed and improved the Power Groove lamp. These lamps are recognizable by their large diameter (2+18 in or 54 mm) and grooved tube shape.


Colors using a halophosphate formulation are usually indicated by WW for warm white, W for (neutral) white, CW for cool white, and D for the bluish daylight white.

Philips and Osram use numeric color codes for tri-phosphor and multi-phosphor colors. The first digit indicates the color rendering index (CRI) of the lamp. If the first digit on a lamp says 8, then the CRI of that lamp will be approximately 85. The last two digits indicate the color temperature of the lamp in kelvins (K). For example, if the last two digits on a lamp say 41, that lamp's color temperature will be 4100 K, which is a common tri-phosphor cool white fluorescent lamp.

BL is used for ultraviolet lamps commonly used in bug zappers. BLB is used for blacklight-blue lamps employing a Wood's glass envelope to filter out most visible light, commonly used in nightclubs. Other non-standard designations apply for plant lights or grow lights.

Halophosphate tubes
Japanese color code Numeric color code Alphabetic color code Color Approximate CRI Color temperature (K)
N/A 29 WW Warm white ≈52 3000
WW 35 W White ≈56 3500
W 33 CW Cool White ≈62 4000-4300
N/A 25 N/A Neutral/Universal White ≈75 4000
N N/A N/A Natural Daylight ≈70 5000
D 54 D Daylight ≈75 6500
Deluxe halophosphate tubes
Japanese color code Numeric color code Alphabetic color code Color Approximate CRI Color temperature (K)
L-EDL 27 N/A Deluxe Extra Warm White ≈95 2700
N/A N/A SW GE Soft White (Lower-CRI WWX) ≈77 3000
N/A 32 WWX Deluxe Warm White ≈87 3000
N/A N/A WX Sylvania White Deluxe ≈85 3500
N/A 79 N Natural ≈90 3600
N/A 34 N/A Deluxe White ≈85 3850
W-SDL 38 CWX Deluxe Cool White/Kolor-rite ≈90 4000
N/A N/A C41 GE Cool White Utility (Enhanced CWX) ≈87 4100
N-SDL, N-EDL N/A C50/DSGN50 GE Chroma 50/Philips Colortone 50/Sylvania Design 50 ≈90-99 5000
D-SDL, D-EDL 55 DX Deluxe Daylight/Northlight/Colour Matching ≈88-98 6500
N/A N/A C75 GE Chroma 75/Philips Colortone 75 ≈92 7500
700-series tubes (halophosphate and tri-phosphor blend)
Numeric color code Alphanumeric color code Color Approximate CRI Color temperature (K)
730 SP30/D30/TL730 Warm White ≈75 3000
735 SP35/D35/TL735 Neutral White ≈75 3500
741 SP41/D41/TL741 Cool White ≈75 4100
750 SP50/TL750 Natural Daylight ≈75 5000
765 SP65/TL765 Cool Daylight ≈75 6500
800-series tri-phosphor tubes
Japanese Color Code Numeric color code Color Approximate CRI Color temperature (K)
ELX 825 Sunset White ≈85 2500
ELR, ELC 827, 828 Extra Warm white ≈85 2700, 2800
EX-L, EL, ELK 830 Warm White ≈85 3000
ELW 832 Warm White ≈85 3200
EX-WW, EWW 835 Neutral White ≈85 3500
EW38 838 Neutral White ≈85 3800
EX-W, EW 840, 841, 842 Cool White ≈85 4000, 4100, 4200
EX-N, EN 850 Natural Daylight ≈85 5000
ENW, ENM, ENC 852, 853 Natural Daylight ≈85 5200, 5300
ENK 855 Natural Daylight ≈85 5500
ENX 858 Natural Daylight ≈85 5800
EDW 862 Cool Daylight ≈85 6200
EX-D, ED 865, 867 Cool Daylight ≈85 6500, 6700
ECW, EDK, EDC 872, 874 Cool Daylight ≈85 7200, 7400
EDF, EDX 880 Skywhite ≈85 8000
Multi-phosphor tubes
Numeric color code Color Approximate CRI Color temperature (K)
927 Warm white ≈95 2700
941 Cool white ≈95 4100
950 Natural Daylight ≈98 5000
965 Cool daylight ≈95 6500
Special purpose tubes
Numeric code Alphabetic Code Fluorescent

lamp type

05 N/A Germicidal lamps No phosphors used in these lamps at all, and the enveplope is made of fused quartz instead of glass.

In the American lamp code, the F as in FxxTyy is replaced by a G as in GxxTyy, indicating that it's a germicidal lamp.

08 BLB Black-Light Blue lamps These lamps are similar to the regular black light lamps, except they use wood's glass as a filter to reduce the amount of visible light emitted. These lamps are used for fluorescence effects where less visible light is ideal.
09 N/A Sun-tanning lamps These lamps produce wide or narrow band UV-B radiation
10 BL Black-Light lamps Black light lamps give off long-wave UV-A radiation of around 350-400 nm. They are often used to attract insects to traps. Unlike black light blue lamps, these lamps do not use wood's glass. They use regular soda-lime glass and emit more visible light than BLB lamps.

Common tube ratings[edit]

This section lists the more common tube ratings for general lighting. Many more tube ratings exist, often country-specific. The Nominal Length may not exactly match any measured dimension of the tube. For some tube sizes, the nominal length (in feet) is the required spacing between centers of the lighting fixtures to create a continuous run, so the tubes are a little shorter than the nominal length.

Tube diameter in 18 in (3.175 mm) Nominal length Nominal power (W) Lamp Code
T5 Miniature 6 in (152 mm) 4 F4T5
T5 Miniature 9 in (229 mm) 6 F6T5
T5 Miniature 12 in (305 mm) 8 F8T5
T5 Miniature 21 in (533 mm) 13 F13T5
T5/HE 22 in (560 mm) 14 F14T5
T5/HE 34 in (860 mm) 21 F21T5
T5/HE 46 in (1,200 mm) 28 F28T5
T5/HE 58 in (1,500 mm) 35 F35T5
T5/HO 22 in (560 mm) 24 F24T5/HO
T5/HO 34 in (860 mm) 39 F39T5/HO
T5/HO 46 in (1,200 mm) 54 F54T5/HO
T5/HO 58 in (1,500 mm) 80 F80T5/HO
T8 15 in (381 mm) 14 F14T8
T8 18 in (460 mm) 15 F15T8
T8 2 ft (610 mm) 17 F17T8
T8 2 ft (610 mm) 18 N/A
T8 3 ft (914 mm) 25 F25T8
T8 3 ft (914 mm) 30 F30T8
T8 4 ft (1,219 mm) 32 F32T8
T8 4 ft (1,219 mm) 36 N/A
T8 5 ft (1,524 mm) 40 F40T8
T8 5 ft (1,524 mm) 58 N/A
T8 6 ft (1,829 mm) 70 N/A
T8 single-pin 6 ft (1,829 mm) 38 F72T8
T8 single-pin 8 ft (2,438 mm) 51 F96T8
T8 single-pin 8 ft (2,438 mm) 59 F96T8
T8/HO 4 ft (1,219 mm) 44 F48T8/HO
T8/HO 5 ft (1,524 mm) 55 F60T8/HO
T8/HO 6 ft (1,829 mm) 65 F72T8/HO
T8/HO 8 ft (2,438 mm) 86 F96T8/HO
T12 15 in (381 mm) 14 F14T12
T12 18 in (457 mm) 15 F15T12
T12 2 ft (610 mm) 20 F20T12
T12 3 ft (914 mm) 30 F30T12
T12 4 ft (1,219 mm) 40 F40T12
T12 5 ft (1,524 mm) 65 N/A
T12 5 ft (1,524 mm) 80 N/A
T12 6 ft (1,829 mm) 75 N/A
T12 6 ft (1,829 mm) 85 N/A
T12 8 ft (2,438 mm) 125 N/A
T12 single-pin 4 ft (1,219 mm) 39 F48T12
T12 single-pin 6 ft (1,829 mm) 55 F72T12
T12 single-pin 8 ft (2,438 mm) 75 F96T12
T12/HO 4 ft (1,219 mm) 60 F48T12/HO
T12/HO 5 ft (1,524 mm) 75 F60T12/HO
T12/HO 6 ft (1,829 mm) 85 F72T12/HO
T12/HO 8 ft (2,438 mm) 110 F96T12/HO
T12/VHO 4 ft (1,219 mm) 115 F48T12/VHO
T12/VHO 6 ft (1,829 mm) 160 F72T12/VHO
T12/VHO 8 ft (2,438 mm) 215 F96T12/VHO

European energy-saving tubes[edit]

In the 1970s, Thorn Lighting introduced an energy-saving 8 ft retrofit tube in Europe. Designed to run on the existing 125 W (240 V) series ballast but with a different gas fill and operating voltage, the tube operated at only 100 W. Increased efficiency meant that the tube produced only 9% lumen reduction for a 20% power reduction.[7] This first energy-saving tube design remains a T12 tube even today. However, follow-on retrofit replacements for all the other original T12 tubes were T8, which helped with creating the required electrical characteristics and saving on the then new (and more expensive) polyphosphor/triphosphor coatings, and these were even more efficient. Note that because these tubes were all designed as retrofit tubes to be fitted in T12 fittings running on series ballasts on 220–240 V supplies, they could not be used in 120 V mains countries with inherently different control gear designs.

Type Diameter (in, mm) Nominal length (ft, m) Nominal power (W) Notes
T8 1.0, 25 2, 0.6 18 Retrofit replacement for 2 ft T12 20 W
T8 1.0, 25 4, 1.2 36 Retrofit replacement for 4 ft T12 40 W
T8 1.0, 25 5, 1.5 58 Retrofit replacement for 5 ft T12 65 W
T8 1.0, 25 6, 1.8 70 Retrofit replacement for 6 ft T12 75 W
T12 1.5, 38 8, 2.4 100 Retrofit replacement for 8 ft T12 125 W

Around 1980 (in the UK, at least), some new fluorescent fittings were designed to take only the newer, retrofit tubes (the lamp holders are designed not to take T12 tubes, except for 8 ft length). The earlier T12 halophosphate tubes still remained available as spares until 2012. They fit in older fittings and some modern fittings that employ twist lock lamp holders, even though the modern fittings were not electrically designed for them.

US energy-saving tubes[edit]

In the 1970s, 34-watt energy-saving F40T12 fluorescent lamps were intoroduced in the United States. In the 1980s, T8 32-watt lamps were introduced,[8] but unlike the T8 tubes introduced in Europe, these T8s are not retrofits and require new matching ballasts to drive them. These ballasts were originally magnetic, but most today are electronic. The energy-saving T12 lamps are made to operate on ballasts designed for 40-watt F40T12 lamps, though some F40T12 ballasts are not be designed to operate these lamps, and can overheat if energy-saving lamps are used. Running an energy-saving T8 tube with a ballast for T12 will reduce lamp life and can increase energy consumption.[9] Conversely, a T12 tube on a T8 ballast will usually draw too much power and so may burn out the ballast, unless it is within the range that particular ballast can compensate for. The tube type should always match the markings on the light fixture.

Type Diameter (in, mm) Nominal length (ft) Nominal power (W) Lamp Code Notes
T5 0.625, 16 4 49 F49T5 Retrofit replacement for 4 ft T5HO 54 W
T8 1.0, 25 4 25 F32T8/25w Retrofit replacement for 4 ft T8 32 W
T8 1.0, 25 4 28 F28T8


Retrofit replacement for 4 ft T8 32 W
T8 1.0, 25 4 30 F32T8/ES Retrofit replacement for 4 ft T8 32 W
T8 1.0, 25 2 17 F17T8 Ballast-swap replacement for 2 ft T12 20 W
T8 1.0, 25 3 25 F25T8 Ballast-swap replacement for 3 ft T12 30 W
T8 1.0, 25 4 32 F32T8 Ballast-swap replacement for 4 ft T12 40 W
T8 1.0, 25 8 59 F96T8 Ballast-swap replacement for 8 ft T12 75 W single-pin
T12 1.5, 38 4 "25" F40UTSL Retrofit replacement for 4 ft T12 40 W on underpowered residential-grade rapid start magnetic ballasts. These are F40CW lamps made with

lighter cathodes that can only handle a lower amount of power. They will function as a standard 40 W lamp on full-power ballasts, but may not last as long. These lamps are typically rated to last for 12,000 hours on a residential-grade ballast and only 6000 hours on a commercial-grade one.

T12 1.5, 38 4 32 F40T12/ESP Retrofit replacement for 4 ft T12 40 W
T12 1.5, 38 4 34 F34T12


Retrofit replacement for 4 ft T12 40 W
T12 1.5, 38 8 60 F96T12/ES Retrofit replacement for 8 ft T12 75 W single-pin
T12 1.5, 38 8 95 F96T12/HO/ES Retrofit replacement for 8 ft T12 110 W high-output

T5 tubes[edit]

In the 1990s, longer T5 tubes were designed in Europe (making it to North America in the 2000s), in addition to the shorter ones (mentioned above) already in use worldwide. Like the European modular furniture, display cabinets, ceiling tile grids, etc. they were designed for, these are based on multiples of the 300 mm (11.8 in) "metric foot" instead of the 12 in (305 mm) imperial foot, but are all 37 mm (1.5 in) shorter to allow space for the lampholder connections within the 300 mm modular units, and for much easier insertion into and removal from troffer lights within a grid.

Tube diameter is 58 in (15.875 mm) Length Nominal power (W) Notes
High-efficiency High-output
T5 563 mm (22.2 in) 14 24 Fits within a 0.6 m modular unit
T5 863 mm (34.0 in) 21 39 Fits within a 0.9 m modular unit
T5 1,163 mm (45.8 in) 28 54 Fits within a 1.2 m modular unit
T5 1,463 mm (57.6 in) 35 80 Fits within a 1.5 m modular unit

The T5 diameter is nearly 40% smaller than T8 lamps and almost 60% smaller than T12 lamps. T5 lamps have a G5 base (bi-pin with 5 mm spacing), even for high-output (HO and VHO) tubes.[10]

See also[edit]


  1. ^ Funke and Oranje, "Gas Discharge Lamps"; N.V Philips' Gloeilampenfabrieken (1951)
  2. ^ "The T5 Fluorescent Lamp: Coming on Strong". 1 September 2003. Retrieved 20 February 2020.
  3. ^ "Covington, E. J. The Story Behind This Account of Fluorescent Lamp Development". Archived from the original on 24 March 2007. Retrieved 28 September 2008.
  4. ^ "The Fluorescent Lamp – Gas Fillings". lamptech.co.uk. Retrieved 30 August 2023.
  5. ^ "Lawrence Berkeley National Laboratory: T-8 lamp retrofits". Archived from the original on 16 September 2008. Retrieved 28 September 2008.
  6. ^ "Lawrence Berkeley National Laboratory: History and problems of T12 fluorescent lamps". Archived from the original on 16 September 2008. Retrieved 28 September 2008.
  7. ^ Thorn Lighting Technical Handbook
  8. ^ "4-Foot T-8 Fluorescent Lamp Upgrading". Retrieved 2 November 2022.
  9. ^ "Energy Codes". 1 November 1995. Archived from the original on 22 May 2011.
  10. ^ Lighting Research Center, "T5 Fluorescent Systems", [1], accessed 11-30-2009.