There are some very rare plants which can grow without light - such as some cacti that grow in the deserts. However, for any regular plant, light is a must-have. While some plants need less light and others need more, all plants do need light as it helps them with processes such as photosynthesis and the generation of chlorophyll. Plants can grow without using a ‘grow light’ if you grow them outdoors, as the sunlight would be sufficient. However, grow lights promise optimal growth because you can control them in any way you wish to.