Linear fluorescent tubes can look deceptively similar. A replacement may have the correct length and pins yet still be unsuitable for the fixture’s ballast or wiring. LED tubes add another decision because some operate through a compatible ballast while others require the ballast to be bypassed.
Use this checklist before purchasing or installing a replacement.
1. Identify the tube family
Look for a printed code beginning with F or a clear T designation. T5, T8 and T12 describe tube families with different diameters. The number traditionally represents eighths of an inch: T5 is approximately 5/8 inch, T8 approximately 1 inch and T12 approximately 1½ inches.
Do not identify the tube by diameter alone. Record the complete marking, including wattage, length or output designation.
2. Measure the full length
Measure from end to end, including pins if appropriate. Nominal descriptions do not always equal the exact physical length. U-bend, high-output, slimline and special tubes require additional measurements.
3. Confirm the base and pin arrangement
Common T8 and T12 tubes may use a G13 bi-pin base, while T5 tubes commonly use G5. Other linear lamps use single-pin, recessed double-contact or specialised bases. Count the pins and photograph both ends.
4. Read the fixture and ballast labels
The ballast controls the lamp and is a critical part of the system. Record:
- Ballast manufacturer and model
- Input voltage
- Supported lamp types and quantities
- Starting method, if stated
- Wiring diagram
- Emergency-ballast information
A wall switch does not necessarily isolate all electrical energy in a fixture. Ballast replacement, rewiring and electrical testing should be performed by a qualified professional using appropriate isolation procedures.
5. Decide which LED-tube method applies
LED tube products are commonly grouped by operating method:
- Ballast-compatible: Designed to work with specific approved ballasts
- Direct-wire or ballast-bypass: Connected to mains after qualified rewiring
- Hybrid or universal: Designed for more than one approved operating method
These labels do not make every product compatible with every fixture. Check the exact manufacturer compatibility list and installation instructions for the selected tube and ballast combination.
6. Check whether the lampholders are shunted
Some direct-wire LED tubes require a particular powered-end arrangement and compatible lampholders. This is an electrical configuration issue, not something to guess visually. The selected product’s wiring diagram must be followed by the installer.
7. Review the required light output
Compare lumens, beam distribution and mounting height. Fluorescent tubes emit light around much of their circumference, while many LED tubes direct light over a defined angle. A lower total lumen value may sometimes deliver useful light efficiently, but the result depends on the fixture and application.
8. Match colour and appearance
Record the existing colour temperature and CRI where available. Replacing one tube with a different CCT can produce an obvious mismatch. Group replacement may be preferable in customer-facing spaces.
9. Check the environment
Confirm suitability for enclosed fixtures, cold rooms, high temperatures, damp locations, food-service areas or emergency systems. Review product certifications and operating-temperature limits.
10. Label modified fixtures
When a fixture is rewired for a direct-wire LED tube, it should be labelled in accordance with the lamp manufacturer’s instructions and applicable requirements. This helps prevent a future user from installing an incompatible fluorescent or LED lamp.
Before ordering, photograph the old tube, its markings, both bases, the fixture label and the ballast label. Bulb World Lighting can help identify suitable lamp options; all rewiring and electrical modifications should be handled by a qualified electrician.