Fiat lux

With my old fluorescent grow lights getting dimmer month by month, I decided it was time to upgrade the lights I use for fostering my seedlings in the basement.

The more light they get, the stronger seedlings will be when it's time to move outside

    Although we may like the idea of starting seeds on a sunny windowsill, the sunlight that comes through a window isn’t really bright enough to grow strong seedlings. Even if I had an unobstructed south-facing window, which I don’t, plants couldn’t get more than 6,000 lux through the glass. In comparison, outdoor light can reach 120,000 lux in full sun.

Light through the window isn't strong

     As plants stand farther back from the window, available light drops off quickly to only 3,000 lux at one foot. Screens filter out light too, and short winter days reduce light exposure.

    Artificial light does more for seedlings that are destined to grow outdoors. My young plants will need 20,000 to 25,000 lux to grow robustly.

Shorter and chunkier is better

    For years I’ve used fluorescent lights for my seedlings. My first set-up was a cheap fluorescent shop light hung from a board held up by bricks. It did the job. Later I bought a four-shelf unit with two fluorescent tubes at each level. The lamps could be moved up and down, which was convenient for keeping them no more than six inches above the leaves—again, light levels drop off sharply with distance from the source. The bulbs didn’t generate heat; even leaves touching them came to no harm. I could use regular fluorescent tubes for these lamps or choose tubes that offer a color spectrum favored by growing plants.

    Over the years, I’ve had trouble maintaining these fluorescent fixtures. Replacing the bulbs and the starters that are needed for fluorescents turned out to be tricky. This winter I was down to one and a half working lamps.

    Meanwhile, for upstairs I upgraded to a T5 fluorescent, twice as intense as the T12s in those basement lights. I can appreciate the difference. The light looks brighter, and seedlings stay huskier under it.

T5 fluorescent under a windowsill

    Marijuana growers may opt for the even greater intensity of HID (high intensity discharge) bulbs, metal halide or high pressure sodium. This is the very bright light you’ll see in clandestine windowless growing areas in TV crime dramas. My friend Prudence urges me to try growing marijuana, but I’m not up to that level of indoor production yet. HIDs generate a lot of heat, which means you can’t let leaves get as close to them. 

    The next wave in grow lights is LEDs. The Gardeners Supply catalog offers LED light stands for around $250 to $300 per shelf. That’s more than I wanted to spend. Instead, I bought a heavy duty wire shelving unit and four LED shop lights—total cost $280. 

New LEDs. I hung some lamps at an angle to keep them closer to the foliage.

It was easy to hang the lamps from the shelves with the hardware provided. They certainly provide more light than the fluorescents, and they should last for my lifetime. Will their light spectrum work for my seedlings? Stay tuned.