Carotenoids

Carotenoids are fat-soluble, strongly coloured (usually yellow, orange or red) substances found in many plants. The probable use of carotenoids to the plant is that they harmlessly absorb ultraviolet light and oxygen, which otherwise might damage the plant's tissues. This is rather similar to their usefulness to animals including humans; all the carotenoids are strong antioxidants, preferentially dissolving in various cell membranes including the cell wall and protecting those membranes from damage caused by oxidation and free radicals from other sources including nuclear radiation (there is always some nuclear radiation in the environment, from cosmic rays and radioactive substances in the diet).
Beta-carotene is of course a carotenoid; however, it is rather different because the body has a use for beta-carotene in the production of vitamin A. No individual one of the other carotenoids is essential in the diet, but it is probable that one's health would be drastically impaired if one did not have any of them in the diet.
Carotenoids have many specific uses. Lutein and zeaxanthin have specific effects on protecting the eye (particularly the retina) from damage; lycopene has specific use in protecting the prostate, particularly against cancer. Alpha and gamma carotene are protective in the lungs specifically; and beta carotene, apart from its use as a precursor to vitamin A, also helps the lungs. However, high levels of any and all carotenoids in the diet, whether from food or supplements, help protect against many problems including the problems of aging and specifically cancer.
Carotenoids are found in the diet in all vegetables, although they ae not always obvious, but in general terms any plant food that is orange or yellow will be high in carotenoids; examples are carrots, yams (sweet potatoes) and various squashes; also fruits such as melons. Lycopene is a bit more difficult to find in food, as it isn't quite so obvious; it is bright red, which means that foods high in lycopene might be confused with foods high in various proanthocyanidins. The common food highest in lycopene is tomatoes.
Carotenoids are best absorbed from juices or cooked food, as both processes help break down plant cell walls and make the carotenoids more absorbable. Carotenoids are also a great deal better absorbed if eaten with at least some fat, as they are themselves fat-soluble. Carotenoid supplements are therefore ideally taken with a meal that contains some fat, or with any oil supplements that you might be taking.