So, you have a home greenhouse—congratulations! There is nothing quite like stepping into your own warm, glass-walled oasis while the weather outside is doing its worst. It feels a bit like magic. But if you’ve noticed your winter seedlings looking a bit tall, skinny, and fragile (a classic case of what gardeners call “leggy”), or your favorite potted flowers refusing to bloom, you aren’t doing anything wrong. Your greenhouse is just missing one simple thing: enough usable light.