Fluorescent Lamp Formats
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 F##T##, where F is for fluorescent, the first number indicates
the power in watts (or where lamps can be operated at different power levels, the length in inches), the T
indicates that the shape of the bulb is tubular, and the last number is the diameter in eighths of an inch
(sometimes in millimeters, rounded to the nearest millimeter).
Typical diameters are T12 or T38 (11/2" or 38.1 mm) for residential bulbs with old magnetic ballasts, T8 or T26
(1" or 25.4 mm) for commercial energy-saving lamps with electronic ballasts, and T5 or T16 (5/8" or 15.875 mm)
for very small lamps, which may even operate from a battery powered device.
FLUORESCENT TUBE DIAMETER DESIGNATION COMPARISON
Tube diameter Tube diameter
Extra
designations measurements
Imperial Metric Inches Millimeters Socket Notes
2 Osram's Fluorescent Miniature (FM)
T2 N/A /8" approx 7
tubes only
Slim lamps. Power ratings and lengths
4
T4 N/A /8" 12 G5 bipin not standardized (and not the same)
between different manufacturers
Original 4–13 W range from 1950s or
earlier.
5
T5 T16 /8" 15.875 G5 bipin Two newer ranges high efficiency (HE)
14–35 W, and high output (HO) 24–80
W introduced in the 1990s
G13 bipin/Single
8 From the 1930s, more common since
T8 T26 /8" 1" 25.4 Pin/Recessed Double
the 1980s.
contact
9
T9 T29 /8" 11/8" 28.575 Circular fluorescent tubes only
G13 bipin/single pin,
12 1 Also from the 1930s, not as efficient as
T12 T38 /8" 1 /2" 38.1 recessed double
new lamps.
contact
17 Large size for F90T17 (preheat) and
T17 N/A /8" 21/8" 53.975 Mogul Bipin
F40T17/IS (Instant Start)
17 Recessed Double General Electric's Power Groove tubes
PG17 N/A /8" 21/8" 53.975
Contact only
Reflectors
Some lamps have an internal opaque reflector. Coverage of the reflector ranges from 120 degrees to 310
degrees 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##".
VHO lamps with reflectors may be coded as VHOR. No such designation exists for the amount of reflector
degrees 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 (30 degrees of opening, give or take) are used in
the food industry for quality control purposes, to allow robotic inspection of cooked goods.
Aperture lamps have a clear break in the phosphor coating, typically of 30 degrees, to concentrate light in one
direction and provide higher brightness luminance 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 draw more electrical 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 (17/8" or 21/8"), grooved tube shape
and an R17d cap on each end of them.
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 diameter of the circle (not circumference or watts) being the
first number, and the second number usually being 9 (29 mm) for standard fixtures.
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. BLB is used for blacklight-blue lamps commonly used in bug
zappers. BL is used for blacklight lamps 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 rendition index 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)
27 Warm white 50–79 2700
33 Cool white 50–79 4100
83 Medium warm white 80 3000
84 Cool white (high CRI) 80 4100
29 (discontinued) Medium warm white 50-70 2900
32 (discontinued) Medium cool white 50-70 3200
34 (discontinued) Cool white (pinkish) 50-70 4000
Tri-phosphor tubes
827 Warm white ~85 2700
835 White ~85 3500
841 Cool white ~85 4100
850 Sunlight ~85 5000
865 Cool daylight ~85 6500
880 Skywhite ~85 8000
Multi-phosphor tubes
927 Warm white ~95 2700
941 Cool white ~95 4100
950 Sunlight ~98 5000
965 Cool daylight ~95 6500
Special purpose tubes
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 WATTS
T5 6 in, 150 mm 4W
T5 9 in, 225 mm 6W
T5 12 in, 300 mm 8W
T5 21 in, 525 mm 13 W
T8 18 in, 450 mm 15 W
T12 2 ft, 600 mm 20 W
T12 2 ft, 600 mm 40 W
T12 4 ft, 1200 mm 40 W
T12 5 ft, 1500 mm 65 W, 80 W
T12 6 ft, 1800 mm 75 W, 85 W
T12 8 ft, 2400 mm 125 W
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.
Tube Diameter In 1⁄8 In
Nominal Length Nominal Watts Notes
(3.175 Mm)
T8 2 ft, 600 mm 18 W Retrofit Replacement for 2 ft T12 20 W
T8 4 ft, 1200 mm 36 W Retrofit Replacement for 4 ft T12 40 W
T8 5 ft, 1500 mm 58 W Retrofit Replacement for 5 ft T12 65 W
T8 6 ft, 1800 mm 70 W Retrofit Replacement for 6 ft T12 75/85 W
T12 8 ft, 2400 mm 100 W Retrofit Replacement for 8 ft T12 125 W
By around 1980 (in the UK, at least), most new fluorescent fittings were designed to take only the newer,
retrofit tubes (end-caps won't take T12 tubes, except for 8 ft length). The earlier T12 tubes still remain available
as spares but only fit in older fittings.
US energy saving tubes
In the 1990’s, various energy saving tubes were introduced in the US, but unlike the T8 tubes introduced in
Europe, they are not retrofits and required 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.
Tube Diameter in 1⁄8 in (3.175 mm) Nominal Length Nominal watts Notes
T8 2 ft 17 W
T8 4 ft 34 W
T8 5 ft 40 W
T8 8 ft 59 W
T12 4 ft 25 W Shoplite
New T5 tubes
In 1990s, a new set of T5 tubes was designed. The lengths of these tubes are designed to fit within 300 mm
modular units (such as modular ceilings, modular cupboards, etc.), each being a multiple of 300 mm, less a
constant fixed amount for end-caps and the construction of the unit end. The use of T5 tubes (rather than T8 or
T12) allows the tubes to be fitted into smaller spaces, and the smaller light source also enables more accurate
control of beam direction by means of optics (reflectors and lenses in the luminaire).
Each tube length is available in both a lower power high efficiency (HE) version, and a higher power (but lower
efficiency) high output (HO) version. The loading (watts per unit length) of the T5 HE tubes is similar to the
original 4/6/8/13 W T5 tubes, and some manufacturers produce a range of fittings spanning both these ranges
of tubes.
When originally developed in Europe, operation from both switchstart series ballasts and electronic ballasts
was specified, but electronic ballasts were rapidly taking over at the time, particularly in the commercial lighting
space where these tubes are most commonly used, and switchstart series ballast operation is no longer
specified by manufacturers, only electronic ballasts.
Tube Diameter in 1⁄8 in (3.175 mm) Length Watts HE Watts HO Notes
563 mm
T5 14 W 24 W Fits within a 600 mm Modular Unit
(22.2 in)
863 mm
T5 21 W 39 W Fits within a 900 mm Modular Unit
(34.0 in)
1,163 mm
T5 28 W 54 W Fits within a 1200 mm Modular Unit
(45.8 in)
1,463 mm
T5 35 - 49 W 80 W Fits within a 1500 mm Modular Unit
(57.6 in)
T5 fluorescent is the first linear lamp type to be served only by electronic ballasts. It is smaller than T8 and T12
lamps, with a miniature bi-pin base. It is notable for its lumens-per-watt efficiency, due to its peak light output
occurring at 35 °C (95 °F) air temperature. There are three types of ballasts available for T5 lamps: instant start,
rapid start, and programmed start electronic ballasts.
T5 lamps operate at frequencies greater than 20 kilohertz. Most manufacturers claim that their T5 ballasts have
a total harmonic distortion (THD) of less than 15%. Most T5 ballasts are very quiet and carry class ―A‖ sound
ratings. Dimmable ballasts exist for T5 lamps.
Energy efficiency
Care must be taken when comparing efficiency of T5 and earlier technology fluorescent tubes. Whilst T5 can
appear to be more efficient than T8 in datasheets, this is actually due to different test methods. Output of T8
tubes is measured using magnetic ballasts, whereas output of T5 tubes is measured using electronic ballasts.
When T8 tubes are run on electronic ballasts, they are about the same efficiency as T5 HE tubes.
The T5 lamp provides peak light output at 35 °C (95 °F) air temperature. (By contrast, the T8 and the T12 lamps
provide peak light output at a 25 °C [77 °F] ambient air temperature.) The T5 lamp has a higher lumens-per-
watt efficiency than a T8 lamp of about the same wattage, in a space where there is little or no air circulation.
Also, the so-called "high output" T5 lamps have lower efficacy than the "high efficiency" series (lamp nominal
powers 14, 21, 28 and 35 W). Care is needed to specify the latter lamps, if very high energy efficiency is wanted.
T5 lamps are a popular energy-efficiency measure, due to their potential to cut energy use in lighting by more
than 65%.
4’ Linear Fluorescent Bulbs Lumen Output
28 Watt T5 2900 Lumens
54 Watt T5 5000 Lumens
25 Watt T8 2209 Lumens
32 Watt T8 2850-3100 Lumens
34 Watt T12 1930-2800 Lumens
40 Watt T12 1980-3300 Lumens
T5 luminaires that utilize a sleep mode or motion sensors to operate can generate even larger cost savings. In a
2008 field test in a warehouse scenario, using a standard T5 lighting system as a replacement to a metal halide
system had potential cost savings of 23%. However, when using a T5 system with a sleep mode to replace a
metal halide system, building owners had potential cost savings of 34-75% depending on sleep and wake
control modes used.
Mercury content
The T5 lamp has a low mercury content. Each new generation of fluorescent lighting technology, including the
T5 generation, has been able to function with less mercury, but perform with the same or greater efficiency.
The lamp has a coating on the inside of the glass wall that stops the glass and phosphors from absorbing
mercury. This barrier coating reduces the amount of mercury needed from approximately 15 mg to 3 mg per
lamp. Since mercury absorption causes the lamp’s light output to depreciate over its life, the coating helps to
keep light levels much closer to initial output—only 5% depreciation in the first 40% of its life.
Glare
Since T5 are smaller than T8 bulbs, but produce roughly the same amount of light, their surface luminance is
higher than T8 lamps. Glare can be an issue, especially with high output bulbs (5000 lumens), but can be
mitigated by placing the bulbs out of direct line of sight, or using louvers or diffusers.
Differences from other fluorescent lamps
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), while T8 and T12 lamps use a G13 base (bi-pin with ½ inch/13 mm
spacing).
T5 tubes operate at a higher than ideal temperature for the purposes of regulating the mercury vapor pressure
in the tube. A fluorescent lamp’s "cold spot" is the area where the internal glass wall temperature is at its
lowest. It is the temperature of the coldest spot which effectively sets the mercury vapor pressure for the whole
tube. Unlike a T8 or T12 fluorescent lamp, where the cold spot is in the middle, in T5 lamps it is at the tube end
which is marked with the rating label, in the extended space behind the filament. By having this extended area
outside of the discharge run cooler, this reduces the mercury vapor pressure in the whole tube to more ideal
levels. T5 lamps generally last for 20,000 hours, as compared to T8 lamps, which last for 15,000 hours.
T5 lamps are both electrically and physically incompatible with T8 and T12 lamps. These differences in
dimension prevent T5 lamps from being used as replacements for T8 and T12 lamps, unless the existing
luminaires are electronically converted, via T5 retrofit conversion, to high frequency operation, so that they can
accept the T5 lamps. Note that conversion kits will invalidate any standards conformance (such as UL) which a
luminaire has, unless the manufacturer will re-certify their product with a particular conversion kit.
