Ask ten reef keepers whether T5 or LED is better and you will get ten answers, most of them delivered with real conviction. Both will grow corals. Both have produced tanks that stop you in your tracks at a shop or club meet. The useful question is not which is "best", but which suits the way you run your reef: your budget, the space above the tank, the room it sits in, and how much fiddling you actually enjoy.
Here is how the two compare on the things that matter most to reef keepers in the UK.
Two very different light sources
T5 is fluorescent tube technology. High-output tubes run from a ballast in standard lengths — 24W at 60cm, 39W at 90cm, 54W at 120cm and 80W at 150cm — and most reef tanks run a bank of four to eight tubes in a fixture or hood. The light spreads evenly along the whole tube, and you build your spectrum by mixing them: a couple of blues, a white or two, maybe an actinic or a purple. Nothing is adjustable once the tubes are in.
LED fixtures use clusters of diodes and are, by nature, point sources. Coverage depends on how many clusters you have and how high the unit is mounted, which is why you sometimes see bright patches under the clusters and dimmer corners at the ends of a long tank. In exchange, you get control: dimming, ramping, colour channels, moonlight settings and phone apps that let you tweak things you probably should not tweak every week.
Plenty of reefers now run a hybrid — a couple of LED units for punch and shimmer, with one or two T5 tubes to fill in shadows and even out the coverage.
Upfront cost: what you pay on day one
A quality T5 fixture is usually the cheaper way into serious reef lighting, particularly on a tank over a metre long, where you may need two or three LED units to cover the footprint properly. That said, a good dimmable T5 fixture with decent reflectors is not a cheap item either, and the budget end of both markets is a false economy. Cheap LED units often deliver far less usable light than the box suggests.
Do the sums honestly before you buy:
- Count the cost of the fixture, plus mounting or hanging hardware.
- For T5, add a full set of tubes to your first-year figure — you will replace them within twelve months.
- For LED, check the warranty length on the fixture and, separately, on the power supply.
- Factor in a controller if the fixture needs one to dim.
The second-hand market is worth a look in both camps. T5 fixtures go cheaply because people are moving the other way; LED units hold their value better but are still often a sensible buy.
Heat, ventilation and tank temperature
A bank of six 54W tubes is 324W of lighting, and a fair amount of that energy ends up as heat in the room and, to a degree, in the water. In a well-insulated British home during a warm spell, that can be enough to push a tank from a comfortable 25°C into the 27s by late afternoon. You then need fans across the surface, a chiller, or the lid propped open.
LEDs still produce heat — energy in equals energy out — but much of it leaves through the heatsink above the tank rather than radiating down into the water. Tank temperature is usually easier to manage, though the room still warms a little and cooling fans on the fixture make noise. If you have ever lost sleep over summer tank temperatures, this is one of the strongest arguments for LED.
Shimmer, spread and the look of the tank
T5 gives flat, even, diffuse light with almost no shimmer. Corals are lit uniformly from every angle, which is easy on the eye and forgiving of aquascapes with lots of overhangs. Some keepers find it slightly lifeless.
LED produces the rippling glitter lines that make a reef tank look like the sea, because the light comes from small points. That look is hard to beat. It also creates shadowing, which suits some corals and stresses others, and hotspots directly under the clusters. Diffuser panels soften both the shimmer and the hotspots, at the cost of a little punch.
Coral growth and colour
Both technologies grow soft corals, LPS and SPS well. T5 is proven and forgiving: if you get the tube mix roughly right and replace tubes on schedule, you will grow corals without much thought. LED rewards attention. You can tune the spectrum towards heavy blue for fluorescence, dial intensity up or down, and match the look of a shallow lagoon or a deeper reef slope. The risk is constant meddling, or running a deep blue display at low overall intensity and wondering why growth has stalled.
Corals respond to consistency far more than to brand names. Pick a schedule, hold it steady for a couple of months, and judge the results.
A few habits that make LED easier to live with:
- Start low and increase intensity gradually over four to six weeks.
- Borrow or buy a PAR meter, or ask your local club if someone has one to lend.
- Mount the fixture high enough for even spread, but not so high that the sandbed is dim.
- Photograph the tank on the same settings each month. Growth is easier to see in photos than in person.
Running costs across a year
Electricity is the big ongoing cost, and the honest answer is that it depends on the fixture, not the technology. A 324W T5 bank running eight hours a day uses roughly 2.6 kWh daily. A comparable LED setup often draws less for similar light output, but a cheap fixture running flat out can easily match it. Check your current unit rate on your bill and multiply it out — the figure is usually more sobering than expected.
Then add consumables. T5 tubes should be replaced every nine to twelve months, because output and spectrum drift well before a tube visibly fails, and a full set of six adds up year after year. Reflectors need cleaning, and old ones lose their efficiency. LEDs have no tubes to change, but drivers, fans and power supplies can fail, so buy from a brand with UK support and a decent warranty. A plug-in energy monitor is a cheap way to see exactly what your lighting is costing.
Which is right for your tank?
If you are setting up your first reef on a budget, or you have a long tank and cannot stretch to two or three LED units, a well-built T5 fixture is a safe, forgiving choice that will grow almost anything. If you want shimmer, app control, low tank heating and no tube changes, LED is the better fit — and it becomes clearly cheaper to run over several years if you keep the fixture long enough.
For many UK reefers the answer sits in the middle: a hybrid. LED for the blues and the glitter lines, one or two T5 tubes to fill the shadows and even out the coverage. If you would rather not decide today, buy the best fixture you can afford for the dimensions of your tank, keep one variable at a time, and let the corals tell you what is working.
Photo: Jeffry Surianto / Pexels
