I did an experiment concerning this sometime in the past too though it was an accidental discovery that the LED light actually do help plant growth. I was trying to produce fodder for my poultry but mistakenly left the seedlings in a location where the only source of light was an LED light. I noticed that the plant was growing towards the light. I changed the direction and, within a few hours, the plants changed direction again towards the light. So I think it can serve as source of light for growing plants.