Comparing T8 and T5 Fluorescent Tube Lamps for Your Box Turtle’s Habitat


Tube style UV lamps come in a few different varieties. Learn the differences between the most common reptile bulbs: T8, T5, and T5-HO UV lamps

Tube style UV lamps come in a few different varieties. T8, T5, and T5-HO are the most common ones sold for reptiles.

Choosing a fluorescent bulb to use in your reptile habitat is not as simple as it might seem. You’ll find several different kinds of bulbs at the store, each with advantages and disadvantages.

Often the best bulb for you depends on how your habitat is set up and how much UV your pet needs.

If you’ve decided to use the tube-style UV lamps over the compact fluorescents, you’ve eliminated one variable. But you’re still not done.

Fluorescent tubes come in several types, most commonly T8 or T5, although you’ll still find T12s as well. To make things even more confusing, they also come in high-output (HO) versions. In general, most HO lamps you’ll find specifically for reptile use will be T5, although we’ve seen a few T8s labeled as HO.

We’ll focus on comparing standard T8 with both standard and HO T5 lamps.

Quick Overview: How Fluorescent Tubes Work

First a (very) basic look at how these lamps work (not strictly necessary to your choice, so feel free to skip this section if you’d like!):

These lamps contain mercury plus an inert gas like argon in a sealed tube. There are electrodes at each end, and the inside of the tube is coated with a phosphor powder coating. These things work together to produce both UV and visible light.

When you turn them on, electricity flows through the gas between the electrodes. The energy in the electrical current causes the mercury to turn into a gas and release particles of UV light (called photons).

Visible light comes from some of those photons hitting phosphor atoms in the coating. This basic description is true of all fluorescent tubes.

So What Do T8 and T5 mean?

Basically, these designations refer to the diameter and shape of the lamp. The “T” means tube or tubular. The number tells you how many eighths of an inch around they are. So T8 lamps are 8 eighths or 1 inch while a T5 is 5/8-inch in diameter. (The older, T12s, are 12/8″ around, which translates to a diameter of 1.5″).

T5 and T8 lamps are also different lengths. This means they’re not really interchangeable. If you already have a fixture for one size, that’s the kind of bulb you’ll need to buy. One exception is that you can buy retrofit kits to convert a standard T8 fixture to use the short T5 lamp (but only the standard, not the HO).

You cannot change a T5 fixture to fit a T8 bulb. And you can’t use a HO bulb in a fixture intended for standard lamps (well, technically you can, but you’ll most likely shorten the lifespan of both the lamp and the fixture).

Different manufacturers of reptile lighting make different combinations of lamps. So make sure you know what you’re buying.

Standard T8 vs Standard T5

Standard T5 bulbs are slightly shorter than (as mentioned) but more efficient than similarly sized T8s:

  • A standard 48-inch T8 uses 32 watts to produce about 2,850 lumens of light.
  • The comparable T5 is 46 inches (2 inches shorter) and uses 28 watts to produce about 2,900 lumens.
  • You’ll save about 12.5% energy but get about the same amount of light.

Also, T5 lamps in general work better at higher temperatures than T8s do, and they don’t have the flicker problem that many people complain about with the T8s.

An example of a regular T5 bulb made specifically for reptiles is the Zilla Desert 50 T5. Zilla Desert 50 also comes as a T8 lamp.

One common complaint about T5 vs T8 is that the T5s often cost much more. But that’s not always the case. As you can see from the above links, PetCo sells them both for about the same price.

Remember, you can buy conversion kits to convert a T8 fixture to work with a standard T5 tube.

Standard T8 vs T5 High Output

T5-HO lamps are not actually more energy efficient on a per-bulb comparison to T8s (in fact, they’re slightly less efficient). But if you need or want a brighter light and higher UV output, using one T5-HO is more efficient than using two T8s.

Plus, the UV rays of a T5-HO bulb reach farther than a standard bulb. Doubling up on standard T8s won’t help the rays penetrate farther. If you need to put your lamps farther away from your pet, the HOs are invaluable.

An example to illustrate:

Zoo Med’s ReptiSun 5.0 lamps come in both standard T8 and T5-High Output versions. Both lamps emit 5% of their UV as UVB, but the T5-HO emits more UV overall and thus more UVB. And because the rays penetrate farther, the recommended distance from your pet is up to 24 inches, as opposed to 12 inches for the T8.

Because of this, you have more flexibility in where to place your lamp.

One thing to consider: The high output lamps do produce more heat than the standard ones. Depending on the size of your habitat and where you put the lamp, you may need to adjust your heat setup to keep the temperature in the right range.

And unlike standard T5s, you cannot retrofit a T8 ballast to fit a T5-HO lamp.

T5-HO Lamps and UVC Exposure

One final note: A few years ago there was some concern about T5-HOs producing UVC rays (which are harmful to all animals). At the time, manufacturers could not guarantee their lamps were not emitting UVC, and reptile enthusiasts recommended against using them. Today, according to manufacturers, reptile bulbs are made with a special glass that blocks UVC but lets both UVA and UVB through. This makes them safe to use.

Box turtle eating strawberryHopefully this helps you understand the different tube style UV lamps you can buy for reptiles and makes your decision a little easier.


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