Lighting Your Seedlings

Finally! In spite of the foot of snow we received this past weekend, spring is just around the corner. For those with late frost-free dates, it’s finally time to start our seeds. Back in 2009 I posted a series of articles about seed starting. (You can find them in the category drop box at right.) However, years have passed and things have changed.

While I still stand behind everything I said back in 2009, we who garden in 2021 have the advantage of new technology. Back in the day, I used basic shop lights—normal cool white fluorescent tubes—to grow my seedlings. Now I’ve switched out the fluorescents for LEDs, and my little seedlings couldn’t be happier.

To see why, let’s look at the light intensity from each type of bulb. Light intensity is measured in lumens. My old 40-watt fluorescent tubes put out 2300 lumens. My new LEDs are much brighter, emitting 5000 lumens. Moreover, the output of aging fluorescents steadily diminishes, especially at either end of the tube, while LEDs remain constant.

Whichever light source you use, be sure to position them so that your plants are as close as possible to the bulbs—within an inch or two—as the amount of light they’ll receive quickly falls off with distance.[i]

Fluorescent lights have a limited life-span, averaging 10,000 hours. This will be shorter if you frequently turn them off and on, as you would do daily when starting seeds.[ii] LEDs, on the other hand, last much longer, for 50,000 to 100,000 hours. Keep this in mind while pricing your options.

LEDs use significantly less electricity to produce their brighter light. This is partly because little energy is wasted as heat, partly because the light is all aimed downward where it’s wanted, and partly because they’re just that more efficient. Thus, they’re better for the environment, both in resources needed in their manufacture, and in their energy needs.

And while we’re on the topic of the environment, remember that fluorescent lights contain both mercury and phosphor, toxic substances that require specialized disposal of worn out bulbs. (I wonder how many people actually bother to haul their used tubes to the toxic waste disposal?)

If LEDs have a downside, it’s their initial price. They typically cost more. However, remember that they can last 5 to 10 times as long as a cheap fluorescent tube. Beside, prices are coming down. We recently picked up a couple of LED fixtures for well under $20 each. Considering how well they work and how long they last, I consider it a worthwhile investment.


[i] I find it easiest to raise my trays to start with, then lowering them as needed as the seedlings grow taller. To facilitate this, I try to group my seedlings so that those with similar heights occupy the same tray.

[ii] Leaving the lights on for more than 14 hours a day can cause veggie seedlings, especially spinach and lettuce, to bolt later in life. Besides, plants need both light and dark for healthy growth.

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