Reptile Lighting Guide: UVB, Heat & Photoperiods Explained

Lighting is not optional for reptiles — it's life support. Inadequate UVB causes metabolic bone disease, one of the most common preventable diseases in captive reptiles. Get lighting right from day one.

Why UVB Is Non-Negotiable

Reptiles need UVB light (290-320 nm wavelength) to synthesize vitamin D3 in their skin. Without D3, they cannot absorb calcium from their diet — regardless of how much calcium you supplement. The result is metabolic bone disease (MBD): soft, rubbery bones, jaw deformities, pathological fractures, muscle tremors, seizures, and death. It's painful, disfiguring, and 100% preventable. UVB does NOT pass through glass or plastic. Mesh screens block 30-50% of UVB. Overhead mounting is essential — UVB must come from above. UVB from the side can cause eye damage.

Types of UVB Bulbs

Linear fluorescent T5 HO (high output) — gold standard. Best penetration, widest coverage, longest lifespan (replace every 12 months). Recommended brands: Arcadia ProT5, Zoo Med ReptiSun T5 HO. Linear fluorescent T8 — older technology, weaker output, replace every 6 months. Compact fluorescent (coil bulbs) — unreliable UVB output, can cause eye problems (photokeratoconjunctivitis). Avoid — they're inconsistent and dangerous. Mercury vapor bulbs (MVB) — provide both UVB and heat in one bulb. Can be used for large enclosures and basking zones. Very intense — must be used at correct distances and monitored. UVB LEDs — emerging technology, not yet proven reliable for most species. Stick with fluorescent or MVB.

UVB Index by Species (Ferguson Zones)

Zone 1 (shade dwellers, UV index 0-0.7): crested geckos, leopard geckos, many snakes (corn snakes, ball pythons), amphibians. Arcadia ShadeDweller (7% UVB) or Zoo Med ReptiSun 5.0 T5. Zone 2 (partial sun/basking, UV index 0.7-1.0): bearded dragons (low end), blue tongue skinks, tortoises, chameleons (montane). Arcadia 6% or Zoo Med ReptiSun 5.0 T5. Zone 3 (open sun/basking, UV index 1.0-2.6): bearded dragons (high end), uromastyx, sulcata tortoises, green iguanas. Arcadia 12% or Zoo Med ReptiSun 10.0 T5. Zone 4 (mid-day baskers, UV index 2.6-3.5+): same as Zone 3 species with higher basking platform placement. Many species need a UV gradient — place the UVB bulb to overlap with the basking zone on one side only, creating a UVB gradient across the enclosure. The animal should be able to escape UVB entirely on the cool side.

Heat and Basking

Reptiles are ectothermic — they depend on external heat for all bodily functions. A proper thermal gradient is essential:

Specific requirements by common species: Bearded dragon: basking 100-110°F (38-43°C), warm 85-95°F (29-35°C), cool 75-80°F (24-27°C), night ≥65°F (18°C). Leopard gecko: basking 90-95°F (32-35°C via under-tank heater), warm 85-90°F (29-32°C), cool 75-80°F (24-27°C), night ≥70°F (21°C). Ball python: basking 88-92°F (31-33°C), warm 80-85°F (27-29°C), cool 75-80°F (24-27°C), night ≥72°F (22°C). Crested gecko: room temperature species, 72-78°F (22-26°C). Stress above 82°F (28°C). Heat sources: halogen flood bulbs (best for daytime basking — produces IRA/IRB most similar to sun), deep heat projectors (DHP — good for nighttime, no light), ceramic heat emitters (CHE — no light, nighttime use), under-tank heaters/heat mats (UTH — ONLY for species that absorb heat through their belly like leopard geckos. MUST be used with thermostat). ALL heat sources must be on a thermostat. An unregulated heat source can kill your reptile in hours. Dimming thermostat for light-emitting heat sources. On/off or pulse-proportional for non-light sources. Digital thermometers with probes on both warm and cool sides. Temperature gun for surface readings. No stick-on analog thermometers — dangerously inaccurate.

Photoperiod (Day/Night Cycle)

Consistent day/night cycles regulate hormones, activity, feeding, and brumation cycles. Tropical species: 12 hours light, 12 hours dark year-round. Temperate species: summer 14 hours light, winter 10 hours light (to simulate seasons). All lights (UVB, basking, ambient) should be on timers. Consistent timing matters — erratic lighting stresses reptiles. NO colored lights at night — no red, blue, or "moonlight" bulbs. Reptiles can see the light, and it disrupts their sleep cycle. If nighttime heat is needed, use a lightless source (DHP, CHE).

Common Lighting Mistakes

No UVB at all — fastest path to MBD. UVB through glass/plastic — blocks 100% of UVB. UVB bulb not replaced — UVB output decays long before the bulb burns out visibly. T5: 12 months, T8: 6 months. Mark the replacement date on the bulb with a Sharpie. Basking spot too cool — reptile can't digest food properly (gut impaction risk). Basking spot too hot — thermal burns (common with unregulated heat sources). No temperature gradient — reptile can't thermoregulate. Colored night lights — disrupt sleep. Improper distance — UVB too far (ineffective) or too close (eye/skin damage). Follow manufacturer distance guidelines. Using coil/compact UVB bulbs — poor output, eye risks. No thermostat on heat sources — a fire hazard and animal killer.