Fluorescent Grow Light - Testing the Output

by Will
(Soldotna, Alaska)

I have heard that fluorescent grow 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 fluorescent grow lights, 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!

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(10 week update below)

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Hi everyone, Jason from Jason's Indoor Guide here. When I got started with hydroponic gardening more than 24 years ago, my first garden used rockwool cubes and B.C. Nutrients....and I remember thinking to myself yeah, sure, there may be a lot of advantages to gardening with hydroponics, for example there are very few pest problems, therefore very little pest control, no weeding, no plowing or tilling the soil, no soil testing or having to add things into the garden soil, no watering the garden....but for someone who just wants to grow their own vegetables and have more control over their food supply and the quality of the food that they eat, the cost of constantly having to buy grow media and hydroponic nutrients makes this an expensive hobby for most people...

Epic Nutrient Change

I suppose when you take into consideration how much money you save NOT having to buy food at the grocery store, it is surely cheaper to grow your own food hydroponically even with the cost of high quality nutrients. Nevertheless, I didn't have a whole lot of money to work with and I needed to make my efforts as affordable and effective as possible....and in the last 24 years I HAVE learned a thing or two!

As you browse through Jason's Indoor Guide, you will notice all of the systems that I use personally are homemade systems. As I got 3 or 4 years of experience under my belt, I quickly adopted a preference to standing water systems and systems that use expanded clay pellets or lava rock, because the media is re-usable and it eliminates a huge operating expense. So once a hydroponic system is built, garden maintenance is minimal- check and adjust the nutrient solution daily, and to change it completely every 2 weeks....and the biggest operating cost is the hydroponic nutrients. (and the electric bill, lol)...

Homemade Cloner

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Unfortunately, I have been gardening for over 24 years and I have only just recently mastered this difficult skill....and even then, only because I happened to find a very easy to follow, high quality technique and decided to follow the instructions to the letter. I produced more high quality compost in just one week than I was able to use in a whole year! If you can master the technique, I highly recommend it. It is one of the top 3 things you can do to increase the productivity of your food production efforts, while at the same time decreasing the amount of effort required to grow all of your own food, and decreasing the total cost of operating your food production system.

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This solution is aquaponics. If you are serious about producing all of your own food and being self-sufficient, this is the ultimate solution for reducing expenses (as much as possible), reducing the total amount of work required, and maximizing the productivity of your gardening efforts. I have been gardening for over 24 years, and it is the perfect food production solution in my opinion.

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Besides mastering how to make high quality compost, learning aquaponics is one of the top 3 things you can do to increase your garden productivity, reduce your total costs, and reduce your total work. The product that I learned from is called Aquaponics4you. With all of my hydroponic gardening experience, the first time I came across the Aquaponics4you product I knew immediately that it was something very special! Place an aquaponics system outdoors and use the sun instead of grow lights, and you have reduced every garden expense to nearly ZERO!

The Same System/ 10 Weeks Later!

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