Except for a few creatures in the depths of the oceans and deep under the earth (and, of course, parasites, saprophytes, viruses, bacteria, and maybe a few others that I don’t know about), the plants and animals that the average person recognizes as such all need light to survive. This is subject to variation – what might kill one species might not be enough for another – but light, either sunlight, or artificial light is necessary for our well-being. Green plants need light to make their food; then we (or the animals that we eat) eat a lot of them.
We humans need sunlight to create vitamin D; I know that we can take this vitamin in liquid or pill form, but it’s not half as much fun as a walk in the sunshine. I guess I should confess that as a Canadian, I feel that light, especially sunlight, is not far behind love and freedom as being essential to my happiness.