Non-negotiable for this particular lizard
If any pet reptile can be said to run on ultraviolet light, it is the green iguana. Wild iguanas spend their days stretched along branches in full tropical sun, and their bodies are calibrated for that exposure. Indoors, no window and no ordinary bulb substitutes: glass filters UVB out of sunlight entirely, and a lamp that merely looks bright may emit almost no UVB at all. A proper UVB source is therefore part of the iguana's life-support system, on the same level as its food and water, and choosing a green iguana means budgeting for quality lamps and their regular replacement from the very first day.
Why iguanas are hit hardest without it
An iguana's diet stacks the odds against it. As a strict herbivore eating leaves and flowers, it takes in food that is naturally low in calcium and contains no vitamin D3 whatsoever — every scrap of D3 must be manufactured in its skin under UVB. At the same time, a young iguana grows at extraordinary speed toward an adult length of well over a metre, laying down bone continuously, so its calcium demand is enormous precisely when the supply chain is most fragile. Remove the UVB and the gut stops absorbing calcium no matter how good the diet is; the body then mines the skeleton to keep the blood supplied, and the skeleton loses.
The early damage is easy to miss
Metabolic bone disease in an iguana announces itself quietly. The lower jaw may begin to feel soft and rubbery and to sit slightly askew; fine tremors appear in the toes and limbs; the legs can look swollen while actually weakening; appetite drops and the iguana grows lethargic, basking listlessly instead of moving around the enclosure. Any of these signs in a green iguana warrants a veterinarian promptly rather than a wait-and-see week, because deformities that set in during growth — bent spines, shortened jaws, fractured limbs — cannot be fully undone later. Caught early and given corrected lighting and veterinary care, an iguana can recover a great deal; caught late, it cannot.
Getting UVB right across a big enclosure
Scale is the challenge: an iguana needs a long UVB tube or a mercury vapour lamp covering its basking shelf, not a small bulb glowing in one corner. Position the lamp at the manufacturer's stated distance from the basking spot — UVB strength falls away sharply with distance — with no glass or plastic screen in between, and keep the rest of the enclosure shadier so the iguana can move out of the beam when it chooses. Replace tubes on schedule, since output fades months before the light fails, and whenever weather and security allow, supervised time in real sunshine outperforms every lamp made. Check the basking area's warmth too, because an iguana that is too cool will not bask long enough to use the light.
Because iguana health checks lean so heavily on lighting history, keep your lamp types, distances and change dates in KinsLe's Pet Passport, the one packet that carries the iguana's records to the vet, to boarding or to any new keeper.