Fluorescent tubes generally have a two-pin fitting at both ends of the tube and generally, length goes hand in hand with wattage – the longer the tube the higher the wattage.

T12 38mm (G13) Fluorescent Tubes

The largest size T12 (38mm) is no longer being manufactured, however, they did use the same G13 cap as the T8 fluorescent tube which means that you can replace the T12 tubes with the more efficient T8 of the same length. See T8 section below for suitable alternatives.

T8 26mm (G13) Fluorescent Tubes

Standard size T8 (26mm) tubes use the G13 fitting with 13mm between the two pins.

T5 15mm (G5) Fluorescent Tubes

The small T5 (16mm) tubes use the G5 fitting with 5mm between the two pins.

T4 12mm (G5) Fluorescent Tubes

The undercabinet T4 (12mm) tubes use the G5 fitting with 5mm between the two pins.

T2 7mm (W4.3) Fluorescent Tubes

The ultra-slim T2 (7mm) tubes use a fitting called a W4.3 with 4.3mm wide push-fit fitting.

Colour Temperature

Although most lamps emit white light, this can vary from a cosy warm white to a cold white according to the colour temperature of the lamp. The following chart shows the code numbers used for some of the most popular types:-

Colour Temp Colour Code Designation Application
2700K 827 very warm white Similar light to incandescent light bulbs, giving a warm cosy feel
3000K 830 warm white The colour of most halogen lamps. Appears slightly whiter than ordinary incandescent lamps
3500K 835 white The standard colour for many fluorescent and compact fluorescent tubes
4000K 840 cool white Gives a more clinical or high tech feel
6000K 860 daylight Fluorescent or compact fluorescent lamps simulating natural daylight.
6500 865 cool daylight Extremely white light used in specialist daylight lamps
Colour Temperature Codes (for illustration only, colours may not be exact)

you can read more about colour temperature here.

Colour Rendering Definition

The Colour Rendering Index is an industry-standard reference to a light bulb on how well it renders colours of objects it is illuminating. Codes range from 0 to 100, the higher the number the more vivid and lively things look under that light. The lower the CRi rating the more ghostly (faded, dead) objects appear.

If you want your items and people to look good, then high CRi is required. High CRi light bulbs generally cost more to buy and cost more to operate as they have low lumen output per watt consumed. Low CRi light bulbs put out low-quality light, but are very cheap to operate as they have high lumen output per watt consumed.

5 4 votes
Article Rating
Notify of
Newest Most Voted
Inline Feedbacks
View all comments
June 28, 2020 10:30 am

Thanks for clearing up a query that was giving me a headache. Was trying to find a 4ft tube with a 38mm diameter which is apparently the old style tube and hard to find as discontinued. You can now use the newer T8 tube which is 26mm diameter but with the same end fittings. Many thanks.

August 15, 2020 5:24 pm

Why don’t they put the color of the light on the tube. ? So I know what color to buy again.

October 9, 2020 8:59 am

Dose the fluorescent tube size include the pins

Richard Latham
September 9, 2021 12:38 pm

Im Trying to build a moveable wall of 8 ft x 6 ft with a florescent tube 1 ft apart the whole way down the wall is this possible with just the tube showing not the whole tin housing 

Chris B.
Chris B.
February 4, 2022 8:09 pm

I’d really like to send an email to someone to ask for advice but I can’t locate an email address. Basically I need to order 2 x F16W 135 T8 warm white. What product code?

March 24, 2022 5:35 pm

How do i replace an old starter for a 48inch tube?

June 23, 2022 4:23 pm

Help please I need to replace a crompton 13w 835 A01 fluorescent tube tight measuring 65cm or 23 inches without pins. Thank you.