T5 Versus T8 LED Tube Retrofit A Practical Guide
Identifying what is already installed, choosing the right tube, and the ballast question.
In This Guide
Identifying What Is Already There
T5 and T8 describe the tube diameter in eighths of an inch. A T8 is one inch across; a T5 is five eighths, noticeably slimmer.
Length matters as much as diameter. The common lengths are 600mm, 900mm, 1200mm and 1500mm, and a building fitted out over several decades will usually contain more than one.
Survey before ordering. A conversion that stalls because one length was missed costs more in return visits than the tubes did.
The Ballast Question
Fluorescent fittings contain a ballast to start and regulate the lamp. LED tubes come in versions designed to work with an existing ballast, and versions that require the ballast to be bypassed.
Neither approach is universally right. Keeping the ballast is faster to install but leaves a component in circuit that will eventually fail. Bypassing is more work up front and simpler afterwards.
Tell your supplier what is in the fitting. We will confirm the correct tube version in writing rather than leaving the electrician to discover it on the ladder.
Why Retrofit Rather Than Replace
Replacing luminaires means ceiling work, disposal and in many buildings a scaffold. Retrofitting tubes into existing fittings avoids all of it.
The trade-off is that you inherit the existing fitting's optics and its condition. In a building where the fittings are sound, retrofit is almost always the better economics.
Planning The Change
Change a whole run at once rather than lamp by lamp. Mixed old and new tubes in one field of view make the new ones look wrong.
Order by part number, not by description. Our tubes are part-numbered by length and diameter so a repeat order references a part rather than a sentence.
Keep the protective packing on until the tube is at the fitting. Tubes are damaged in transit and in handling far more often than they fail electrically.
Where Tubes Are The Wrong Answer
If the existing fittings are corroded, mechanically damaged or in a wet area with failed seals, retrofitting good tubes into bad fittings wastes them.
If the lighting layout was wrong to begin with - too few fittings, badly placed - a retrofit preserves the original mistake at lower running cost. That is sometimes acceptable and should at least be a decision.
Product ranges covered in this guide
Products Discussed In This Guide
Questions About This Topic
How do I tell T5 from T8?
By diameter. T8 is one inch across, T5 is five eighths and looks noticeably slimmer. Measure an existing tube before ordering.
Do I need to bypass the ballast?
It depends on the tube version. Tell us what ballast is in the fitting and we will confirm the correct tube in writing before you order.
Which lengths do you make?
600mm, 900mm, 1200mm and 1500mm in both T5 and T8. Ask us to confirm current stock for the combination you need.
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Design GuideHave A Specification Question
Send it by email with the application and the quantity. A written answer from someone who knows the range beats an hour of searching.