Frequently asked questions on T5 lighting


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What are T5 lights and are they as good as the hype surrounding them suggests? We've got the answers to some of the most frequently-asked questions.

What are T5 lights?

T5 is simply a collective term for a narrow-diameter fluorescent light tube. Standard 1" fluorescent tubes are sometimes called T8s. T5s run from a special ballast, similar (but different) to the type used for standard fluorescent bulbs.

Why are they better than normal fluorescent tubes?

The makers claim that certain T5s are roughly three to four times more effective than a standard fluorescent bulb of similar wattage. Therefore, they're being marketed as a replacement for the large banks of standard fluorescents used over many reef tanks. By using T5s you'll be able to use fewer tubes than before, and squeeze much more light power under your hood.

Does the light they produce look different?

Yes, T5s produce a "flatter" light, like that produced by a standard fluorescent, rather than an intense directed spot of light like a metal halide. The light levels throughout the tank are more uniform, but you don't get the natural-looking rippling light effect on your substrate you get from a metal halide. Some reefkeepers reckon they lack the "punch" of metal halides for penetrating deep water, so many use a combination of the two types together. Compared to a standard fluorescent, they're considerably brighter to look at.

Are they any good for corals?

They appear to work well in reef tanks and are fast becoming very popular with modern reefers. Experts reckon the light produced may not match that of metal halides but can still be sufficient to get decent coral growth, even in the more demanding SPS corals. The size and coloration of corals from the T5-lit tanks we've seen is very close to that from tanks lit by metal halides.

However, in very deep tanks you might need to confine the light-loving corals towards the upper layers of the tank to ensure they get plenty of light.

Do they have any advantages over metal halides?

Fluorescents like T5s get very warm but the makers claim that they "don't give off radiant heat", so they're less likely to overheat the aquarium than halides. However, they still get almost hot enough to fry an egg on, so they must have more effect upon water temperature than the producers claim. Some can be installed within the hood, so they're handy if space is limited, or if you're unable (or unwilling) to suspend a luminaire from your ceiling.

According to D and D Aquarium Solutions, their T5 bulbs should last for up to 15,000 hours with only a 20% drop off in output. This works out at about 1250 days (more than three years) based on a 12-hour photoperiod. Aquatic Solutions claim 18 months for their "double" tubes. This is far longer than either metal halide or standard fluorescent lamps.

However, as all T5s are still fairly new and we've not seen any long-term data on how long the actual spectrum produced remains useful for corals it might be wise to wait and see on any lifetime claims for T5s.

Virtually all other bulbs eventually deteriorate and we would expect the same to apply to T5s. Indeed, we've heard that some users believe they have already noticed some minor deterioration in their bulbs' output.

How many do I need?

The number and combination of bulbs you add largely depends on what you are keeping. You'll probably be looking at four to six for the average tank, but you might get away with less if you're keeping inverts that are tolerant of lower light levels, such as zoanthids, Pachyclavularia, Leather corals and corallimorphs (mushroom anemones). If you're considering swapping your halides for T5s, D and D Aquarium Solutions reckon you ought to use three 54w T5s to replace each 150w metal halide.

Do they actually work out cheaper than metal halides?

Individually, they're cheaper to buy, but you may need more of them - maybe six or more if the tank is large. Costs can therefore work out similar to metal halides. You could save a few quid on replacement bulbs, though. Some T5 bulbs can be yours for as little as tenner, but you'll be lucky to pick up a metal halide bulb for less than 50 quid.

How do the running costs compare?

By our calculations, based on the recommendations of T5 distributors for the number of bulbs to use, electrical running costs are similar, and potentially slightly higher than with metal halides.

The biggest savings will come to those who currently have a large number of standard fluorescents. T5s kick out more watt-for-watt so you could save a few quid on electricity if you're thinning out the number of bulbs by installing fewer T5s.

What sorts are available?

There are several different designs: stylish luminaire fittings, which include a built-in ballast, reflector and several bulbs, need to be suspended from the ceiling; slimline units, like those from STM and D and D with a ballast and one or two bulbs, are designed to sit under the hood, while canopies like the models from Arcadia and Aquatic Solutions sit on the top of the tank, replacing the hood.

All of those on the market look rather similar. Are there any significant differences?

There are differences in the types of ballast used, which may have some bearing on performance, as well as minor differences in the build quality of the actual light unit itself. However, the most critical differences are in the quality and design of the bulb and reflector used.

There are several different brands of bulb on the market, with each manufacturer making different claims about performance. D and D claim that their bulbs use a superior "A1 phosphor mix" and are the spectra designed specifically for use on aquaria. It's a good idea to use a mixture of bulbs to get the spectrum and light quality you're after. Ask your retailer.

Experts reckon that the gull-wing style of w-shaped reflector is best, because it directs around the tube back to the tank, rather than pointing it back at the bulb.

Can you grow aquatic plants under them?

Yes, there are some bulbs on the market with spectra designed specifically for stimulating plant growth.

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