Untrue. Many holoparasitic and myco-heterotrophic plants do not need light, the most famous example of which is probably Rafflesia arnoldii :
Well, parasitic and heterotrophic plants need light indirectly, parasiting on a plant that photosynthesises. :P
Well, myco-heterotrophs, as the name suggests, parasitise a fungus, which itself needs no light (e.g. the ghost orchid). Some of these plants even get their nutrients from fungi which themselves parasitise other fungi! The point at which light is necessary can be quite a number of steps up in the food-chain.