Fluorescent-lamp formats

For other types of lightbulb mounts and sockets, see Lightbulb sockets.

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

Lamps are typically identified by a code such as FxxTy, where F is for fluorescent, the first number (xx) indicates either the power in watts or length in inches, the T indicates that the shape of the bulb is tubular, and the last number (y) is the diameter in eighths of an inch (sometimes in millimeters, rounded-up to the nearest millimeter). Typical diameters are T12 or T38 (1+1⁄2 in or 38 mm) for residential lamps with magnetic ballasts, T8 or T26 (1 in or 25 mm) for commercial energy-saving lamps with electronic ballasts, and T5 or T16 (5⁄8 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		1⁄4 approx.	7	WP4.5×8.5d	Osram's Fluorescent Miniature (FM) tubes only Sylvania Luxline Slim T2 Linear
T4		1⁄2	12.7	G5 bipin	Slim lamps. Power ratings and lengths not standardized (and not the same) between different manufacturers
T5	T16	5⁄8	15.9	G5 bipin	Original 4–13 W range from 1950s or earlier. Two newer ranges high efficiency (HE) 14–35 W, and high output (HO) 24–80 W introduced in the 1990s
T8	T26	1	25.4	G13 bipin/single pin/recessed double contact	From the 1930s, more common format since the 1980s.
T9	T29	1+1⁄8	28.6	G10q quadpin contact	Circular (circline) fluorescent tubes only
T10		1+1⁄4	31.75	G13 bipin
T12	T38	1+1⁄2	38.1	G13 bipin/single pin/recessed double contact	Also from the 1930s, not as efficient as new lamps.
T17		2+1⁄8	54	Mogul bipin	Large size for F90T17 (preheat) and F40T17/IS (instant start)
PG17		2+1⁄8	54	Recessed double contact	General Electric's Power Groove tubes only

Reflectors

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. Often, a lamp is marked as a reflector lamp by adding the letter "R" in the model code, so a F##T## lamp with a reflector would be coded as "FR##T##". Very high output (VHO) lamps with reflectors may be coded as VHOR. No such designation exists for the amount of reflector coverage the lamp has.

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.

Slimline lamps

Slimline lamps operate on an instant start ballast and are recognizable by their single-pin bases.

High output/very high output lamps

High-output lamps are brighter and are driven at a higher electric current, have different ends on the pins so they cannot be used in the wrong fixture, and are labeled F##T##HO, or F##T##VHO for very high output. Since about the early to mid-1950s to today, General Electric developed and improved the Power Groove lamp with the label F##PG17. These lamps are recognizable by their large diameter (2¹/₈"), grooved tube shape and an R17d cap on each end.

Other tube shapes

U-shaped tubes are FB##T##, with the B meaning "bent". Most commonly, these have the same designations as linear tubes. Circular bulbs are FC##T#, with the outer diameter of the circle (not circumference or watts) in centimeters being the first number and the second number referring to the tube size.

Colors

Color is usually indicated by WW for warm white, EW for enhanced (neutral) white, CW for cool white (the most common), and DW for the bluish daylight white. BL is used for ultraviolet lamps commonly used in bug zappers. BLB is used for blacklight-blue lamps employing a woods glass envelope to filter out most visible light, commonly used in nightclubs. Other non-standard designations apply for plant lights or grow lights.

Philips and Osram use numeric color codes for the colors. On tri-phosphor and multi-phosphor tubes, 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.

Halophosphate tubes
Numeric color code	Color	Approximate CRI	Color temperature (K)
29	Warm white	~52	3000
35	White	~56	3500
33	Daylight/Cool White	~66	4300
25	Natural/Universal White	~75	4000
54	Tropical Daylight	~75	6500
Deluxe halophosphate tubes
Numeric color code	Color	Approximate CRI	Color temperature (K)
27	Deluxe Extra Warm White	~95	2700
32	Deluxe Warm White	~85	3000
34	Deluxe White	~85	3850
79	Deluxe Natural	~93	3600
38	Deluxe Cool White/°Kolor-rite	~92	4000
55	Northlight/Colour Matching	~94	6500
Tri-phosphor tubes
Numeric color code	Color	Approximate CRI	Color temperature (K)
827	Warm white	~85	2700
835	White	~85	3500
840	Cool white	~85	4000
850	Sunlight	~85	5000
865	Cool daylight	~85	6500
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	Sunlight	~98	5000
965	Cool daylight	~95	6500
Special purpose tubes
Numeric code	Fluorescent lamp type	Notes
05	Germicidal lamps	No phosphors used at all, using an envelope of fused quartz.
08	Black-light lamps
09	Sun-tanning lamps

Common tube ratings

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 1⁄8 in (3.175 mm)	Nominal length	Nominal power (W)
T5	6 in, 150 mm	4
T5	9 in, 225 mm	6
T5	12 in, 300 mm	8
T5	21 in, 525 mm	13
T8	14 in, 360-370 mm	14,15
T8	2 ft, 600 mm	18
T8	3 ft, 900 mm	30
T8	4 ft, 1200 mm	36
T8	5 ft, 1500 mm	58
T8	6 ft, 1764 mm	70
T12	14 in, 360-370 mm	14,15
T12	16.5 in, 420 mm	15
T12	2 ft, 600 mm	20
T12	4 ft, 1200 mm	40
T12	5 ft, 1500 mm	65, 80
T12	6 ft, 1800 mm	75, 85
T12	8 ft, 2400 mm	125

European energy-saving tubes

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. 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

In the 1990s, various energy-saving tubes were introduced in the US, but unlike the T8 tubes introduced in Europe, they are not retrofits and require new matching ballasts to drive them. Running a T8 tube with a ballast for T12 will reduce lamp life and can increase energy consumption. The tube type should always match the markings on the light fixture.

Type	Diameter (in, mm)	Nominal length (ft)	Nominal power (W)	Notes
T12	1.5, 38	2	17
T12	1.5, 38	4	34
T12	1.5, 38	5	40
T12	1.5, 38	8	59
T8	1.0, 25	4	25	Shoplite

T5 tubes

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.

Tube diameter is 5⁄8 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, 49	Fits within a 1.5 m modular unit

T5 lamps are approximately 40% smaller than T8 lamps and almost 60% smaller than T12 lamps. T5 lamps have a G5 base (bi-pin with 5 mm spacing).

See also

• Compact fluorescent lamp
• List of light sources
• Fluorescent lamp recycling
• T5 retrofit conversion