Iguanas need a special light in order for their bodies to flourish and be healthy.A source of UVB lighting in an iguana's cage is imperative. UVB lighting helps them synthesize vitamin D3, which is necessary to metabolize calcium in the Iguana's diet. Dietary vitamin D3 cannot be processed by iguanas, and they require a strong UVB source to help their bodies produce it. Without a UVB source, they cannot process calcium properly, and will be prone to Metabolic Bone Disease, an often fatal result of calcium deficiency.
UVB lighting cannot pass through plastic or glass, so the iguana needs to be close enough to benefit from the rays. On the other hand, they can't be placed too close, because they could be burned.