Bearded Dragon Lighting & UVB

Heat, UVB, and visible light do different jobs

Bearded dragons are ectotherms: body temperature depends mainly on their surroundings. Heat supports activity and digestion; UVB enables vitamin D3 production, which helps them use dietary calcium. Bright visible light supports a useful daytime environment, but an ordinary LED or heat bulb does not supply UVB.^{1, 2}

Nutritional metabolic bone disease can result from inadequate calcium, D3, UVB, or heat. Weakness, tremors, a soft jaw, swollen limbs, difficulty walking, or fractures need veterinary assessment. Replacing a bulb alone is not treatment for advanced disease.²

Use a timer for a consistent daytime light cycle, generally around 12 hours as a starting point, with darkness at night. Measure the thermal gradient and basking surface; a bulb’s wattage cannot tell you the temperature your dragon experiences.^{1, 3}

T5 and T8: size and output

The “T” size does not specify a UVB dose. T5 also exists in normal-output versions; choose a reptile T5 HO UVB lamp and compatible reflector/ballast. A plant-growing T5 tube is not automatically a UVB lamp. T5 and T8 tubes are not interchangeable.^{4, 5}

What do 5.0, 10.0, 6%, 12%, and 14% mean?

These labels describe an approximate UVB share of a lamp’s output, not the amount reaching your dragon. A higher percentage does not automatically mean a safer or better setup. Tube power, reflector, mounting distance, mesh, and the closest accessible perch all affect exposure. Even two lamps marked “10%” can deliver different results.⁴

A 24-inch-tall enclosure does not automatically give 24 inches of clearance—substrate, basking rocks, branches, and the dragon’s body reduce it. If the intended system cannot deliver suitable UVB with safe clearance, choose a different lamp or mounting arrangement.

Broad coverage, overlap, and shaded retreats

We prefer a long linear fixture running along the enclosure’s length rather than a small point source. If you use a full-length UVB tube, provide substantial fully shaded areas and solid hides that block direct UVB; every part of the floor should not receive the same exposure. Full-length coverage is our layout preference, not a requirement for every enclosure.

Place useful UVB over the warm basking area so the dragon can access heat and UVB together. It must also be able to retreat to cooler, lower-UV areas. Secure the fixture above the animal, keep glass and plastic out of the UVB path, and account for mesh attenuation. Check exposure at the dragon’s back, not just at the floor.^{3, 6, 7}

A UVI meter, such as a Solarmeter 6.5, helps you map the basking and shade zones. Follow the manufacturer’s bearded-dragon guide for the complete system; a phone light sensor is not a UVB meter.^{6, 7}

Why we prefer tubes over coils and mercury vapor

Coil and compact bulbs

We do not recommend a coil/compact bulb as the main UVB source for a bearded dragon. A small lamp creates a much narrower exposure area than a long tube, making broad coverage harder to achieve. Historical investigations documented eye and skin injuries from certain lamps with excessive or abnormal short-wavelength UV output.^{5, 8}

The accurate term for the reported eye injury is photokeratoconjunctivitis—UV damage to the cornea and conjunctiva, sometimes described as an eye “sunburn.” Those cases do not establish that every modern coil bulb burns the retina. Persistent eye closure, swelling, rubbing, or avoidance after a lighting change warrants prompt veterinary advice and a review of the lamp.

Mercury vapor bulbs

Mercury vapor combines heat and UVB in one localized lamp. We prefer separate heat and linear UVB because a dragon then has broader opportunities to obtain UVB without remaining under one hot basking spot. That flexibility also makes heat and UVB easier to adjust independently. Mercury vapor is not inherently unusable, but it is not our preferred pet-dragon setup.⁹

When should you replace the UVB bulb?

A lamp can still glow after useful UVB output declines. Record the installation date, keep the reflector clean according to its instructions, and check the exact model’s replacement guidance.

Replace sooner if a lamp is damaged or measured output is no longer appropriate. Recheck distances and UVI when changing bulbs or fixtures; a fresh lamp or different reflector can change exposure.^{3, 6, 10}

Our recommended brands and retailer links

• Zoo Med ReptiSun T5 HO 10.0 hood at LLLReptile. Choose a fixture length appropriate to your enclosure and shade plan; the linked 36-inch model is an example, not a universal fit.
• Arcadia ProT5 UVB kit at Reptile Basics. Select the lamp percentage and length for your measured setup.

Read Zoo Med’s system information and Arcadia’s ProT5 guidance before mounting. See our Vitamins & Calcium guide for the other half of bone-health prevention.