UVB strength explained

A UVB lamp’s percentage isn’t the dose your pet gets: on Arcadia’s own chart, its 6% T5 tube reads UVI 4.50 at 12 inches and its 6% T8 reads 1.45. Pick your pet for the lamp strength, basking UV index and distance the sources give.

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What 5.0, 10.0, 6% and 12% mean

Zoo Med’s ReptiSun 10.0 is a 10% UVB lamp. Zoo Med says it reaches 20 in (51 cm) from the lamp, against 12 in (30 cm) for its ReptiSun 5.0, and recommends the 10.0 for larger terrariums and for use above screen covers, which it says can filter out up to 50% of UVB. Arcadia sells 6% lamps for forest species and 12% lamps for desert species, and measures the percentage as part of the lamp’s total light output, after its first 100 hours.

Arcadia says the old advice was simply a 5% lamp for forest animals and a 10% lamp for desert animals, with no thought for the distance to the animal. Its guide now gives a basking UV index (UVI) for each species at different distances, measured with a Solarmeter 6.5.

The tube and the distance change the dose as much as the percentage does. At 12 in, Arcadia’s 6% T5 (UVI 4.50) gives more than its 12% T8 (2.95).

UV index targets

RSPCA gives a basking UVI for each species, from 0.7 for leopard and crested geckos to 3.0–5.0 for bearded dragons and sliders, falling to zero in the shade. Albino bearded dragons, royal pythons and corn snakes get lower targets. A study of 15 lizard and snake species in the wild in the southern US and Jamaica (Ferguson and others, 2010) sorted them into four zones of UVB exposure, from a median UVI of 0.35 in zone 1 to 3.1 in zone 4.

A UV index meter shows what a lamp gives at the basking spot. RSPCA checks a dragon’s gradient with one, and RSPCA Australia says that without one it’s hard to tell whether a light is working properly.

Glass, mesh and distance

UVB doesn’t pass through glass, so the lamp goes inside the enclosure, and most plastics block it too. Mesh blocks part of it, so a tall vivarium or one with a mesh lid may need a stronger lamp.

Keep every light above the animal’s head, not to the side, and at least 4–6 in away, and follow the lamp’s own minimum and maximum distances. Merck puts typical UV lights within 18 in of the basking area, and says mercury vapor lamps can be several feet away. Spot lamps with clear glass faces can give very narrow, intense beams of UV and are best avoided. Guard UV lamps, like heat lamps, against burns.

When to replace a lamp

The sources differ. VCA says to replace UV lights every six months or as the maker directs, even if they still light up. Arcadia says its D3 and D3+ lamps work for a whole year. The British Chelonia Group’s tests found new tubes lose 10–35% of their UVB in the first 100 hours and then decay slowly, so a lamp still good after 3 months is unlikely to need replacing before a year. Check yours with a UV index meter.

RSPCA runs lamps on a plug-in timer, 12 hours on and 12 off. The NSW code asks for at least 6 hours a day from an artificial UV light.