All‑in‑One Bulb or Separate UVB & Heat? The Best Lighting Setup for Every Reptile Keeper

Gabriel Anderson
Jan 31
5 min read

Infographic compares reptile lighting: all-in-one bulb vs. separate UVB and heat. Highlights pros, cons, and best use cases for each.

All‑in‑one reptile bulbs that claim to provide heat, visible light, UVA, and UVB from a single lamp sound perfect—until you look closely at control, safety, and running costs. Separate basking, UVB, and visible‑light sources are a little more work to install, but they give far better flexibility and are now recommended by many vets and advanced keepers for most species.

What Counts as an “All‑in‑One” Bulb?

Most all‑in‑one reptile lamps are mercury vapor or other high‑intensity discharge (HID) bulbs that screw into a ceramic E27 socket.

Output strong visible light, heat, UVA and UVB from one point.
Examples include branded mercury vapor “PowerSun”‑type bulbs and some metal‑halide kits.

By contrast, a separate‑component setup uses:

A basking heat lamp (usually halogen or incandescent).
A linear UVB tube (T5 HO or similar).
Optional LED or daylight fluorescent for extra brightness.

Pros of All‑in‑One Bulbs

1. Simple Hardware

With one bulb you need:

One ceramic fixture.
One power outlet.

That’s attractive for open‑topped tortoise tables or large outdoor pens where mounting a full bar fixture is harder.

2. Strong “Sun‑Like” Output

Mercury vapor and metal‑halide lamps produce:

High infrared heat for basking.
Intense visible light that makes enclosures look bright.
Mid‑ to high‑level UVB suitable for open‑sun species when used at the correct distance.

For big, tall enclosures in cool rooms, a single high‑intensity lamp can be convenient.

3. Fewer Cables and Clutter

One bulb on an arm or stand leaves the top of the enclosure tidier than multiple fixtures, which some keepers prefer for display tanks.

Cons of All‑in‑One Bulbs (And Why Many Keepers Avoid Them)

1. You Cannot Thermostat Them Safely

Most mercury vapor and HID lamps must not be run on dimming thermostats.

They rely on high voltage to start and specific internal pressure to stay lit.
Dimming or rapid on/off cycling can cause flicker, failure, or in rare cases shell rupture.

That means:

Heat output is controlled only by lamp height and wattage, not automatically by a thermostat.
In enclosed vivariums, overheating is a real risk if the room warms up unexpectedly.

2. If One Thing Fails, You Lose Everything

Because heat and UVB come from the same globe:

When it blows, your reptile instantly loses both basking heat and UVB.
Cheaper mercury vapor bulbs have a reputation for inconsistent lifespan—some failing much earlier than the box suggests.

With separate lamps, a failed basking bulb still leaves UVB in place, and vice versa; you have more time to notice and replace it.

3. UVB Beam Is Very Concentrated

All‑in‑one bulbs are point sources: most of their output falls in a cone directly under the lamp.

The basking spot can reach good UVI, but the rest of the enclosure may be comparatively dark and UV‑poor.
Animals wandering off the hot spot may get much less UVB than you expect, especially in wide vivariums.

Linear tubes, by contrast, wash a much wider area with usable UVB and visible light, creating better gradients.

4. UVB Output Is Harder To Predict And Monitor

Tests and keeper reports show that:

UVB output between individual mercury vapor bulbs of the same brand can vary more than with quality T5 tubes.
Output also drops with age, and without a UV Index meter you are guessing.

Separate T5 HO systems have more published distance charts and more consistent UVB decay curves, so it’s easier to keep your animal in the correct Ferguson Zone.

5. Not Ideal for Small or Closed Enclosures

Leading care guides and veterinary factsheets recommend using mercury vapor only over large, open‑topped setups such as tortoise tables.

In a small glass vivarium there may not be enough vertical room to keep the bulb at a safe distance while still hitting the right UVI and temperature.
The lamp can overheat the tank long before the reptile has had enough UVB.

Pros of Separate UVB, Heat, and Visible Light

1. Full Control Over Each Variable

You can tune each component independently:

Choose the UVB strength and distance for your species’ Ferguson Zone (for example, a 6% T5 at 30 cm for a chameleon).
Use a halogen or incandescent basking lamp on a dimming thermostat for precise temperatures.
Add bright, low‑wattage LED bars for extra visible light without changing heat or UVB at all.

This flexibility makes husbandry much easier in real‑world rooms where ambient temperature and light change with the seasons.

2. Better, Wider UVB Coverage

A linear T5 HO UVB tube typically covers 50–70% of the enclosure length, giving:

A clear basking zone with target UVI.
A large “transition” area with moderate UV.
Deep shade areas with almost zero UV.

That natural gradient lets reptiles self‑regulate exposure more like they would in the wild.

3. Easier To Upgrade or Replace

Want a brighter enclosure? Upgrade the visible‑light LED only.
UVI not quite right? Change the UVB tube or adjust its height without touching the basking lamp.
One lamp fails? The others keep doing their job until you swap it.

Over time, this modularity often works out cheaper than replacing expensive combination bulbs regularly.

4. Recommended by Many Modern Guides

Recent veterinary sheets and mainstream care guides now show standard setups as:

One basking/heat source +
One UVB tube matched to Ferguson Zone +
Optional supplementary daylight/LEDs.

Combination lamps are usually listed as a special case for very large, open habitats.

Cons of Separate Setups

More fixtures and cables to mount and manage.
Slightly higher up‑front cost if you buy quality hardware.
Requires a bit more planning to get lamp spacing and angles right.

However, once installed, most keepers find them low‑maintenance and more predictable long‑term.

Which Setup Is Best for You?

All‑in‑One Bulb Works Best When:

You have a large, open‑topped enclosure like a tortoise table or big indoor pen.
The species is a hardy, high‑sun basker (tortoises, uromastyx, some large lizards).
You are comfortable adjusting lamp height frequently and checking UVI with a meter.
You understand that heat will not be thermostat‑controlled and monitor temperatures closely.

Separate UVB + Heat Is Better When:

The enclosure is a standard glass or PVC vivarium with a fixed ceiling height.
You keep multiple species with different UVB or temperature needs.
You want thermostat control over basking temperature for safety.
You prefer wide, even lighting and clear gradients.
You plan to run the same system for years and care about long‑term cost and reliability.

For most new reptile keepers in 2026, separate UVB and heat is the safer, more flexible default, with all‑in‑one bulbs reserved for specific high‑sun species in large, open habitats.

Practical Setup Tips (Any Style You Choose)

Always mount UVB above the animal so it cannot look directly side‑on into the tube or bulb.
Use a UV Index meter to verify that your basking zone sits in the correct UVI range for the species’ Ferguson Zone.
Replace UVB sources on the schedule recommended by the manufacturer, even if they still look bright.
Pair bright visible light with your UVB so enclosures never look dim; reptiles are more active and confident in well‑lit spaces.