Extension services call light the single most important factor in growing plants indoors. It is the energy source for photosynthesis, so a plant in too little light cannot make enough food, however carefully you water or feed it.
Light has three parts worth knowing. Intensity is how bright it is. Duration is how many hours of light the plant receives in a day. Quality is its colour, or wavelengths: plants rely mainly on red and blue light for photosynthesis.
Intensity is the one people misjudge most. Outdoors on a sunny day, light can reach 10,000 to 12,000 foot-candles. Indoors, even a spot right by a window receives a small fraction of that, and a few steps back into the room it falls again. Our eyes adjust so well that a room can feel bright when, to a plant, it is dim.
The next lessons show how to judge each part of light in your own home and what to do when it is not right.
Key points
- Light powers photosynthesis; nothing else can replace it.
- Think in intensity, duration and quality.
- Indoor light is far weaker than it looks to our eyes.
Try this
Stand in the middle of a room that feels bright, then stand right at the window. Notice how your eyes adjust; a plant cannot.
Check yourself
Read more in the reference
Sources
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