"KEEP AWAY FROM SUNLIGHT" WARNING , WHY IT IS WRITTEN ON THE PRODUCTS ?

Ever you think about it, keep away from sunlight / protect from light is written on product. Some food or medical items, like cosmetic items, many of our medicines and other product have a "protect from light" warning on the label. How can light influence products like milk and what does this warning mean in practice? Why they give this warning on the product. How the light can degrade the quality of product. We always learn that light is good for vegetable so how it can be bad. Did these light can make food poisonous?

ANSWER :- 

The photons of light, especially ultra violet photons from sunlight, carry energy that can break chemical bonds.

The bonds in chemicals that make up colours, ie. dye molecules, are most affected - since they create the colour effect by absorbing some photons (of one colour) and not others.

So they have chemical bonds of the correct energy to absorb light, these molecules will eventually be destroyed by strong light and the color will fade - which is what happens to clothes left in strong light. In the case of the fruit juice it will probably lose some of it's strong colour, it may also destroy some of the vitamins - but it's unlikely to make the juice poisonous!