Leopard Gecko UVB Distance: Bulb Strength, Timing & Setup

Why UVB Matters for Leopard Geckos (Even Though They’re “Nocturnal”)

Leopard geckos (Eublepharis macularius) are crepuscular: they’re most active at dawn and dusk, but they absolutely do bask—especially in captivity where they control their comfort through microclimates. UVB isn’t about “making them sunbathe all day.” It’s about giving them the option to synthesize vitamin D3 naturally, support calcium metabolism, and keep bones, muscles, and nerves working properly.

When UVB is missing or poorly set up, you can see a slow slide into problems that look “mysterious” at first:

• •Weak grip, shaky steps, reluctance to climb
• •Soft jaw, rubbery limbs, kinks in the tail (metabolic bone disease/red flags)
• •Poor appetite, slow growth in juveniles
• •Frequent egg binding risk in females with chronic calcium imbalance
• •More subtle: lethargy, low activity, “never comes out”

Dietary D3 can help, but UVB + correct supplementation is the most reliable long-term approach for many keepers—especially if your gecko refuses dusted feeders or you’re trying to keep supplementation conservative.

This guide is built around one goal: dialing in leopard gecko UVB distance (your focus keyword), plus the right bulb strength and timing, so your gecko gets safe, useful UV—without eye irritation, burns, or “it’s there but does nothing.”

The UVB “Triad”: Distance, Strength, and Screen Type (The Setup That Actually Works)

UVB success comes down to three variables working together:

1. Bulb strength (percentage / output class)

Common options are 5–7% (low output) and 10–12% (medium output). Brand naming varies, but the idea is “desert vs forest.” Leopard geckos are low-to-moderate UV users.

1. Distance from bulb to gecko (basking height)

This is the big one. UVB intensity drops quickly with distance. A setup that’s perfect at 10 inches can be pointless at 18 inches—or too strong at 6 inches.

1. Barrier between bulb and gecko (mesh lid, glass, plastic)

• •Glass blocks UVB almost completely.
• •Many plastics reduce UVB heavily.
• •Mesh/screen reduces UVB variably (often 30–60% depending on mesh density and coating).

So when someone says “use a 7% UVB,” the unspoken question is: At what distance, through what screen, and to what basking height?

If you get only one thing from this article: measure your leopard gecko UVB distance from the bulb to the top of the basking surface, not to the floor. Your gecko’s back is what matters, because that’s the exposure plane.

Choosing the Right UVB Bulb: T5 vs T8, Strength, and Best Use Cases

T5 HO vs T8: What’s the difference for leopard geckos?

• •T5 High Output (HO)

Stronger, more efficient, better penetration through mesh, stable output. Usually the best choice for modern setups—but it can be too intense if mounted too close.

• •T8

Weaker and more quickly loses output over time. Can work in smaller tanks or when mounted very close, but often becomes “decor UVB” if the distance is too far or there’s a dense screen.

For most adult leopard geckos in 20–40 gallon enclosures, T5 HO linear UVB is easiest to set up safely and consistently because it provides a usable gradient without requiring the bulb to sit right on top of the gecko.

Strength: 5–7% vs 10–12% (and when each makes sense)

Think in terms of “low-to-moderate UV zones.” Leopard geckos typically do well with a gentle UVB option that creates a small basking opportunity, not a full-tank blast.

• •5–7% UVB (often marketed for “shade-dwelling” reptiles)

Best for:

• •Smaller enclosures (10–20 gallon long, juvenile grow-outs)
• •Tanks where the basking surface is close to the bulb
• •Geckos that are sensitive or have a history of avoiding light

• •10–12% UVB (often “desert”)

Best for:

• •Taller enclosures or basking surfaces farther from the lid
• •Situations where UVB is heavily reduced by a dense mesh top
• •Larger adult setups where you need a more reliable UV zone

Pro-tip: A “desert” bulb doesn’t automatically mean “too strong.” If your basking spot is far from the bulb or your lid blocks a lot of UVB, the stronger bulb may be the safer way to get any useful UVB at all—because you can mount it higher or provide more shade.

Product recommendations (reliable linear UVB)

These are widely used and consistent:

• •Arcadia ProT5 Kit (includes fixture + reflector + bulb)

Good choices: 6% (common leopard gecko pick), 12% if distance/mesh demands it.

• •Zoo Med ReptiSun T5 HO

Common options: 5.0 (lower), 10.0 (higher)

If you can only choose one style, choose a linear T5 HO with a reflector. Coil/compact UVB bulbs create narrow, inconsistent UV zones and are harder to position safely.

Leopard Gecko UVB Distance: Practical Distance Guidelines That Keep You Safe

Because every enclosure is different, distance “rules” should be treated as starting points. Still, keepers need real numbers, so here’s a practical approach that works in most home setups.

First, measure the distance correctly

Measure from the UVB bulb (not the fixture) to the top of the basking surface where your gecko’s back would be when standing.

• •If your gecko climbs onto a rock: measure to the rock surface.
• •If you use a cork tunnel as a “basking shelter”: measure to the top where the gecko’s back sits.
• •If the gecko can climb on decor: make sure the closest possible distance isn’t dangerously short.

Distance ranges (realistic starting points)

These are general guidelines for a linear T5 HO bulb with a reflector:

• •7% / 6% UVB (T5 HO)
• •Through typical mesh: start around 10–14 inches to basking surface
• •No mesh (inside enclosure): start around 12–16 inches

• •12% / 10.0 UVB (T5 HO)
• •Through typical mesh: start around 12–18 inches
• •No mesh (inside enclosure): start around 14–20 inches

For T8 linear bulbs (weaker output), you often need the basking surface closer, commonly 6–10 inches, but this varies a lot by brand and age of the bulb.

Why such a wide range?

Because mesh lids can change everything. A dense screen can cut UVB so much that a “perfect” distance becomes ineffective. A wide-open screen can let much more UVB through. Also, reflectors matter—hugely.

If you want the most accurate setup, use a UV index meter (more on that later). If you don’t have one, the safest approach is:

• •Use a lower-output bulb (6–7%) for most standard tank heights
• •Keep a reasonable distance (not “as close as possible”)
• •Provide heavy shade and hides so the gecko can opt out

Real scenario examples (so you can copy a setup)

Scenario A: Adult Mack Snow leopard gecko in a 36x18x18 (40 breeder style) with mesh lid

• •UVB: Arcadia 6% T5 HO (with reflector)
• •Placement: over the warm side, spanning about 1/3–1/2 of the tank length
• •Basking rock height: set so the top is ~12 inches from bulb through mesh
• •Result: gecko occasionally basks at dusk, better feeding response, stable sheds

Scenario B: Juvenile Tangerine in a 20 long (30x12x12) with mesh lid

• •UVB: ReptiSun T5 HO 5.0
• •Basking spot: ~10–12 inches from bulb through mesh
• •Extra caution: ensure any climbable decor can’t bring the gecko within 6–8 inches

Scenario C: Adult Blizzard in a bioactive 24x18x18 with a very dense mesh top

• •UVB: 12% T5 HO
• •Basking surface: ~14–16 inches from bulb
• •Lots of shade: thick planting/cork + multiple hides
• •Why: dense mesh reduces UVB; stronger bulb compensates while distance prevents overexposure

Step-by-Step: Setting Up UVB the Right Way (With a Safe Gradient)

A leopard gecko UVB setup should create a gradient: a zone where UVB is available and zones where it’s minimal.

Step 1: Pick the UVB style and length

• •Choose a linear UVB bulb (T5 HO preferred).
• •Length guideline:
• •20 long: 12–18 inch fixture is usually plenty
• •40 breeder: 22–34 inch fixture (covering ~1/3 to 1/2 of the enclosure)

You do not need UVB across the entire tank. Your gecko needs options, not a spotlight prison.

Step 2: Position it over the warm side (not centered)

Place UVB so it overlaps the warm side basking area. Leopard geckos use warmth + light cues together.

• •Warm side: UVB + heat
• •Cool side: dimmer, shaded, multiple hides

Step 3: Control leopard gecko UVB distance with the basking platform

Instead of constantly fiddling with the fixture, adjust height with decor:

• •Add a basking rock/slate to bring the gecko closer (if UVB is too weak)
• •Lower the platform or move it out of the UVB beam (if exposure seems too strong)

This makes fine-tuning easier, especially when you upgrade enclosures.

Step 4: Add shaded “escape routes”

Make sure your gecko can fully get out of UVB:

• •At least 3 hides: warm hide, cool hide, humid hide
• •Add cork rounds, plants (real or fake), and rock ledges to break line-of-sight from the UVB

Pro-tip: If your only hide is under the UVB beam, your gecko may “avoid UVB” by avoiding the warm side entirely. That creates a heat problem that looks like a UVB problem.

Step 5: Pair UVB with appropriate heat (essential context)

UVB is not a replacement for heat. Leopard geckos still need proper temperatures for digestion and appetite.

Common modern approach:

• •Halogen flood (daytime heat) + UVB
• •Optional: deep heat projector for daytime warmth (less visible light)
• •Night: usually no heat unless your room drops too low

If you’re using only an under-tank heater, UVB can still be used—but many geckos behave more naturally with overhead heat + light.

Timing: How Many Hours of UVB per Day?

A simple, effective schedule

Most leopard geckos do well with:

• •10–12 hours UVB ON in summer/long-day months
• •8–10 hours UVB ON in winter/short-day months

If you want one set-it-and-forget-it schedule: 10–12 hours daily is fine for most homes.

Should UVB be on at night?

No. Leopard geckos still benefit from a day/night rhythm.

• •UVB OFF at night
• •Bright white basking lights OFF at night
• •If you need night heat, use non-light emitting heat (and keep it modest)

Real-world timing scenario

If you work a 9–5 and want your gecko to see UVB during its active times:

• •UVB on: 11 am – 11 pm (12 hours)
• •This gives evening UVB availability when many geckos emerge

There’s no single “correct” clock time. Consistency matters more than perfection.

UVB + Supplements: Getting Calcium and D3 Balanced (Without Overdoing It)

UVB changes how you supplement. The goal is to avoid both extremes:

• •Too little D3 (calcium can’t be used properly)
• •Too much D3 (hypervitaminosis risk over time)

A practical approach many keepers use:

• •Calcium without D3 available in a small dish (especially for females)
• •Dust feeders with:
• •Calcium (with or without D3 depending on UVB strength and measured output)
• •A multivitamin on a schedule (not daily)

Because brands differ, and individual geckos differ, I recommend this decision framework:

If your UVB setup is solid (linear UVB, correct distance, good gradient)

• •Use calcium without D3 for most feedings
• •Use calcium with D3 occasionally (or not at all) depending on your vet’s guidance and your gecko’s history
• •Use a multivitamin 1–2x/month for adults (more often for growing juveniles)

If you have no UVB (or you’re not confident it’s effective)

• •You’ll rely more on D3 supplementation
• •Consider upgrading to UVB for long-term stability

Pro-tip: If your gecko is under UVB and you’re dusting heavy with D3 at most feedings, that’s where people can accidentally stack too much D3 long-term. UVB is not “extra” on top of heavy D3; it often replaces some of it.

If you have a gecko with a history of metabolic bone disease, or a breeding female, it’s worth discussing a specific supplement plan with an exotics vet.

Common Mistakes (And How to Fix Them Fast)

Mistake 1: Using a compact/coil UVB bulb and calling it “done”

Coils create a small, intense hotspot and poor gradient, and distance is hard to manage.

Fix:

• •Switch to a linear T5 HO with a reflector.

Mistake 2: Mounting UVB on top of glass

Glass blocks UVB.

Fix:

• •Mount above mesh or inside the enclosure (with a guard), never above glass.

Mistake 3: No reflector, weak output, too far away

This is the #1 reason UVB “does nothing.”

Fix:

• •Use a fixture with a reflector.
• •Adjust basking height to hit a useful leopard gecko UVB distance.

Mistake 4: Placing UVB over the entire enclosure

Geckos need control. Full coverage can reduce their ability to escape.

Fix:

• •Cover 1/3 to 1/2 of the enclosure length, over the warm side.

Mistake 5: Letting decor create a too-close climb point

Your gecko doesn’t read your “recommended distance” chart. If it can climb to 4 inches from a strong UVB, it might.

Fix:

• •Audit the enclosure: check the closest reachable point to the bulb.
• •Remove or lower “launch ramps” near the UVB.

Mistake 6: Assuming UVB replaces heat

UVB supports D3. Heat supports digestion and metabolism.

Fix:

• •Ensure warm side temps are correct, and use a thermostat where appropriate.

Comparing UVB Strength Options: Which One Should You Choose?

Option 1: 6–7% T5 HO (most common leopard gecko choice)

Pros:

• •Easier to dial in safely
• •Great for standard-height tanks with mesh lids
• •Usually provides a gentle, usable zone

Cons:

• •In tall setups or dense mesh, it can be too weak unless the basking surface is raised

Best for:

• •Most adult leopard geckos in 20–40 gallon enclosures

Option 2: 10–12% T5 HO (when distance or mesh demands it)

Pros:

• •More reliable UVB in tall cages or with UV-blocking mesh
• •Allows higher mounting while still delivering useful UV

Cons:

• •Can be too strong if mounted close or if the basking surface is high

Best for:

• •Taller enclosures, dense mesh, or when you want a stronger zone with more distance

Option 3: T8 linear UVB (budget/legacy)

Pros:

• •Lower intensity can be forgiving at close distances

Cons:

• •Often ineffective if distance is more than ~10–12 inches or through dense mesh
• •Output declines faster

Best for:

• •Small enclosures where the basking surface is close and you replace bulbs on schedule

Expert Tips: How to “Dial It In” Like a Pro (Without Guesswork)

Use a UV Index meter if you can (the gold standard)

If you want to stop guessing, measure UV. Keepers commonly use a Solarmeter-style UV Index meter.

What you’re looking for is a low UV Index zone at the basking area and near-zero in shaded zones.

Even one day of measuring can answer:

• •Is my leopard gecko UVB distance actually delivering UV, or is the mesh killing it?
• •Did changing fixtures or moving the lamp double my exposure?
• •Is my bulb aging and dropping output?

Replace bulbs on a schedule

UVB bulbs can still light up while producing much less UVB.

General rule of thumb (varies by brand and conditions):

• •T5 HO: replace around 12 months
• •T8: replace around 6 months

If you measure UV, replace when output drops meaningfully rather than by calendar alone.

Watch your gecko’s behavior (and interpret it correctly)

Healthy, normal responses:

• •Basking briefly at dawn/dusk
• •Sitting partly in shade
• •Using hides frequently (they’re geckos)

Red flags:

• •Persistent avoidance of the warm side after adding UVB
• •Eye squinting, keeping eyes closed more than normal
• •Restlessness and constant trying to escape the lit area

If you see red flags:

• •Increase shade immediately
• •Increase leopard gecko UVB distance (raise fixture or lower basking platform)
• •Confirm you’re using a linear bulb, not a compact coil

Pro-tip: Some morphs (especially very light-colored ones like Blizzard, Murphy Patternless, some albinos) can be more light-sensitive. That doesn’t mean “no UVB,” it means “gentler UVB, more shade, and smarter placement.”

Putting It All Together: Example UVB Setups You Can Copy

Setup 1: “Most households” adult leopard gecko (40 breeder, mesh top)

• •UVB: Arcadia 6% T5 HO kit (reflector included)
• •Placement: warm side, covering ~1/3–1/2 of tank length
• •Leopard gecko UVB distance: ~12 inches from bulb to basking surface through mesh
• •Timing: 11 hours/day on a timer
• •Supplements: calcium without D3 regularly, multivitamin on schedule

Setup 2: Smaller 20 long with a juvenile (and lots of climbing decor)

• •UVB: ReptiSun T5 HO 5.0
• •Distance: ~10–12 inches to basking surface through mesh
• •Decor audit: ensure no surface allows closer than ~8 inches
• •Timing: 10–12 hours/day

Setup 3: Taller enclosure or dense mesh (bioactive 24x18x18)

• •UVB: 12% T5 HO
• •Distance: ~14–18 inches to basking surface (depending on mesh density)
• •Shade: heavier planting/cork to create full UV-free retreats

Quick Checklist: Safe Leopard Gecko UVB Distance and Setup

• •Linear T5 HO UVB + reflector (preferred)
• •UVB placed over the warm side, not the whole tank
• •Measure bulb-to-basking-surface distance, not bulb-to-floor
• •Ensure at least one full-shade route and multiple hides
• •UVB on 8–12 hours/day, off at night
• •Avoid UVB through glass
• •Replace bulbs on schedule (or measure UV output)
• •Adjust supplements to avoid stacking excessive D3

If You Want Me to “Sanity Check” Your Exact Setup

If you share:

• •Enclosure size (LxWxH)
• •Bulb brand/type/strength (e.g., Arcadia 6% T5 HO)
• •Whether it’s on mesh or mounted inside
• •Distance from bulb to basking surface
• •Any tall decor the gecko can climb

…I can tell you whether your current leopard gecko UVB distance is likely effective, too strong, or probably getting blocked—plus what the simplest fix would be.