I put my straggling geraniums from outside on the sunny kitchen window this fall, hoping they could be resuscitated. I found an old cobalt blue vase, and have been filling it with tap water, putting in sunlight for a day and then watering all the indoor plants this winter. I have never had such success with my plants. Most recently, we were away for several days and I forgot to water the basil plant, which was just that thing you buy at the grocery store, in a little plug, that's usually mean for instant consumption. It had thrived all winter, but when I neglected it like this I came home to a desiccated "thing." I thought I'd toss it and buy another basil plant and couldn't find one, so I started to water it frequently with the cobalt blue vase water. This poor plant, which really seemed like a goner, has come back to life. I have no idea why this works, but it seems to. I have never tried the blue light in any other way.