Zoo Med ReptiSun T5 HO 10.0 Review (2026): The

Why you should trust this review

I bought this bulb myself and ran it over a real enclosure for a full year. Zoo Med did not provide it. UVB is the one piece of reptile gear where guessing is genuinely dangerous, because too little causes metabolic bone disease and too much causes its own problems, so I wanted to track this bulb across its whole useful life rather than judge it fresh out of the sleeve.

Over twelve months I monitored its output, watched how it aged, and compared it against the Arcadia equivalent that keepers most often weigh it against. I have no stake in either brand. The point was to find out whether the ReptiSun lives up to its reputation as the default UVB tube, and where it genuinely falls short of the premium option.

How we evaluated

The honest core of this test was UVI measurement over time. I installed the 39W 34-inch bulb in a standard T5 HO fixture, set it at a fixed twelve-inch distance over the basking zone, and tracked the UV index at that distance from new through twelve months of daily use. Twelve inches is a common basking distance, so it is the number most keepers actually care about.

I logged the starting output, watched the decline against Zoo Med’s published degradation curve, and noted practical reliability points like starting behavior and end-blackening. I also compared the bulb with and without a reflector, and against the Arcadia ProT5, because the reflector and the competition are the two things that most change whether this bulb is the right buy.

UVI output and degradation over a year

This is the result that matters most and the news is good. At twelve inches the bulb started around a UVI of 4.5 and declined to about 3.4 over twelve months, which tracked the published degradation curve closely. That predictability is exactly what you want from a UVB source, because it means you can trust the replacement schedule rather than guess.

The catch is the tail end. By month twelve the output drifts below a safe basking range for many species, so the twelve-month replacement interval is not a marketing suggestion, it is a real limit. The bulb keeps lighting after its UVB has faded, so you replace on the calendar, not when it dies. Within that year, though, the curve was reliable and matched the numbers Zoo Med publishes.

Reflectors and the Arcadia comparison

The single biggest variable with this bulb is whether you run a reflector. Without one, the usable UVB reaching the animal is meaningfully lower, and in my comparison the bulb’s peak UVI ran about 12 percent under the Arcadia ProT5 at the same distance. That gap is real and worth taking seriously if you are running a bare bulb in a bare fixture.

Add a quality reflector and the picture changes. A reflector redirects output that would otherwise be lost, and it closes much of the distance to the Arcadia. So my recommendation is conditional: this is the right bulb if you already own a good fixture and reflector. If you are buying a complete lighting system from scratch and want maximum output, the Arcadia ProT5 kit is the stronger out-of-box performer, though the ReptiSun bulb is cheaper.

Reliability, stocking, and replacement

On the practical reliability front the bulb behaved well. It started cleanly every time across the year and showed no end-blackening at month twelve, which is a sign of a healthy tube. There were no flickering or failed-start problems, which matters when this is the light keeping your animal healthy.

Its biggest everyday advantage is availability. This is the most widely stocked T5 HO bulb in North American pet retail, which means when the calendar says replace it you can usually walk into a store and buy one the same day. The one stocking caveat is that older retail inventory may sit near its expiry without clear date marking, so it is worth buying from a shop with turnover and checking the bulb is fresh.

Who should buy the ReptiSun T5 HO 10.0?

Buy it if you already own a quality T5 HO fixture and reflector and need a reliable, predictable replacement bulb you can source easily. Buy it if you want output that tracks its published curve and an availability advantage that makes the yearly swap painless. For most established setups, this is the sensible default.

Skip it if you are buying a complete UVB system from scratch and want the highest out-of-box output, where the Arcadia ProT5 kit pulls ahead. Skip running it without a reflector, because bare-bulb output trails meaningfully. And do not stretch it past twelve months, because the UVB fades below useful levels even while it still glows.

The verdict

The ReptiSun T5 HO 10.0 earns its status as the default UVB tube. Over a full year its output declined predictably from 4.5 to 3.4 UVI at twelve inches, matching the published curve, it started reliably with no end-blackening, and it is the easiest UVB bulb to buy on short notice. The honest qualifiers are that it needs a reflector to compete, it sits about 12 percent under the Arcadia ProT5 at peak, and it must be replaced on a twelve-month calendar regardless of whether it still lights. Pair it with a good fixture and reflector, respect the replacement schedule, and it is exactly the dependable, easy-to-source bulb I would keep running.