Generally, lighting globes that are normally used in garden lightings or street lightings could be made from different substances. Mostly common are ABS plastics because of its cheapness. The other is PMMA or acrylic.
Acrylic lighting globes have the advantage of higher stability and solidity against outside weather conditions; thus, under the sun and with continuous exposure for ultraviolet, this does not affect it.
While ABS plastics are affected by UV and that makes it gets yellowed after a period of usage in outside. The reason of that because in manufacturing process there is a substance added to ABS in order to Inhibit flammability which called TBBP. This when get shed to UV makes bromine to be freed and get to the surface of the substance, which get oxidized and makes the outsider shape being yellowed.
On the other hand, acrylic globes are not much expensive than ABS. It has slightly higher value supported with long life, solidity, and stable behavior between the series of outside lighting products.