Fluorescent Light - Testing the Output

by Will
(Soldotna, Alaska)

I have heard that Fluorescent Lights loose their efficiency over time. Is there a meter available to test to see if the light is in the correct light spectrum for tomatoes to grow? If there is, what model and brand would you recommend?

Answer: Will- when you purchase a light bulb, whatever spectrum you decide to go with is the spectrum the bulb will continue to have. What changes over time is the INTENSITY, or strength, of the light output. I have been gardening indoors for 15 years now, and I have never used a light intensity meter. They are quite expensive (at least the ones I've seen), and there are ways that you become comfortable with over time ensure your garden is receiving enough light to achieve your goals.

Basically, the idea is to buy lights that you KNOW produce a lot of light in the usable plant spectrum. Than you want to make sure you replace the bulbs in those lights before they reach 2 years old. Some very serious gardeners replace their bulbs every 12 months, but I find that to be quite wasteful and a bit of an overkill.... most bulb still generate 80% or more of their original output through the second year.

If you have your heart set on using fluorescents, here is the strategy. Any four foot fluorescent shop light will work for clones, seedlings, and plants in the vegetative stage that are 12 or 14 inches tall. When you go to buy bulbs for your fixture, you will want to purchase the bulbs with the highest lumens. Lumens are another measure of usable light, as far as plants are concerned.

Because fluorescent light is so much LESS intense than Metal Halide or High Pressure Sodium light, do not concern yourself with the issue of using blue spectrum light (or cool light) for the veg plants and red spectrum light (warm light) for flowering plants....instead, just stay focused on maximizing the lumens. Keep your plants within two or three inches from the bulbs. Keep the plants directly under the lights. If the plants begin to spread sideways away from the light, add another fluorescent fixture- again, two or three inches above the plants with the plants centered below the lights.

A word of warning- if you are planning to grow flowering plants (which require much more light to grow properly than plants in the vegetative state), expect to have low yields. If you want to grow plants larger than 14 inches tall, or you want larger yields, you may have to move up to compact fluorescents or T5 lights (also known as Tek lights). These lights are made specifically for growing plants, so you can simply purchase the regular bulbs for these lights without much else to consider....but the advice is still the same- replace the bulbs before the end of their second year.

Unfortunately, because of my lack of direct experience in this matter, I cannot recommend a particular model of light meter. However, after reading the above advice, you may decide a light meter is really unnecessary given it's high cost. Either way, I hope this helps you out....and Happy Growing!