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My Fluorescent Light Setup

Contributed article by Jack Honeycutt, © 2002, 2006

Introduction

A few weeks ago I traveled to Seattle Washington from my home here in Portland Oregon (about a 3 hour drive) to a meeting of the Cascade Cactus Society. I traveled to Seattle because the meeting that month was to be at a plant light store and the store owner grows cacti. The store is called The Sun Shoppe; owner Jerry Addington spoke about growing cacti under plant lights (he recommended metal halide lamps). The ceiling of the shop was filled with metal halide lamps, mostly between 500- and 1,000-Watt lamps. He estimated he his lamps would provide 2,000 to 5,000 foot-candles when using the metal halide lamps in actual practice. I am sure this is true, but the display lamps were high up on the ceiling, and I got readings of only 250 to 450 foot candles on the plant stands where the cacti were displayed. (Editor's note: 100 foot-candles is approximately the same as 1080 lux).

He did tell us that he buys cacti and does not grow his own, and he also tries to sell them quickly, before they become elongated. He showered us a few that had been sitting around the shop for a while and that had not sold; they were etiolated and unhappy. Thus, it seems possible ceiling-mounted fixtures do not provide enough light for healthy growth. so maybe he only gets about 400 foot-candles in his shop. No doubt, a much greater illuminance would be obtained in an actual growing setup with the lamps placed closer to the plants. I thought he was a honest and helpful fellow and a friend to all the cactus folks in the society. I did a little impulse cactus buying while in his shop and I recommend a visit if you are ever in that neck of the woods.

Light Bulbs

While taking a reading with my foot candle meter in his shop, I was approached buy a woman (who's name escapes me); she told me she grows all her cacti under fluorescent lights. She says they grow well and flower. I told her that when using a plant light (GE Wide Spectrum Plant and Aquarium Light 48 inches (1220 mm, 40 Watt) I was only getting about 200 or so foot-candles 4-6 inches under the bulb. She told me that she had obtained a great increase in light output when she switched from the cheap $9.95 "shop light" fixtures to a brand with a better ballast.

She also told me that "plant light" bulbs put out few foot-candles, but do give off a lot of light in the red spectrum which is important for encouragine flowering in cacti. She switched from plant lights to a combination of GE 40 Watt Natural Color Kitchen and Bath Ultra bulbs (a "warm" light, with more red than many bulbs), and Philips Cool White Plus (3,200 Lumens, Color Rendering Index 70, Color Temperature 4100K).

When I got home I bought the best 2-bulb, 4-foot (1220mm), 40-Watt fixture (without a reflector) that Home Depot had for sale (about $25.00). And I installed the two fluorescent bulbs suggested by the woman I had spoken to at The Sun Shoppe.. I also bought two other bulbs from GE called "Sunshine Full Spectrum Lights (claimed to simulate noonday summer sun, 2,250 lumens, color temperature 5000K, 90 CRI).

Ballasts

Electronic ballasts have gained in popularity since their introduction in the 1980s. While it is said that the electronic ballasts can produce a little more light, their real claim to fame is that they save energy, using up to 40% less than some magnetic ballasts. As a test I bought the best magnetic ballast Home Depot had for sale (about $11.00), the best Electronic ballast Home Depot had for sale (about $16.00) and a high end electronic ballast (about $40.00) from Grainger. I installed them in the best fixture I had and measured the foot-candle output in the center of the bulb after they were had warmed up for 30 minutes. I took all my measurements at about 4 inches under the bulbs. I used the GE Sunshine (48' GE Sunshine Fluorscent Tube Light Bulb) to establish a baseline.

This created 4 combinations of fixtures:

1. standard ballast supplied with the best Home Depot fixture,

2. best Home Depot standard ballast (same fixture as above)

3. high-end Home Depot electronic ballast (same fixture as above), and;

4. Grainger electronic ballast (same fixture as above).

My readings were similar for all 4 ballasts when using the GE Sunshine, about 2,000 foot-candles. I did get a bit more light with the electronic ballasts, but if I moved my meter just 1/4 of an inch further away the result disappeared. Therefore, unless you are about to replace a old ballast or your energy bills are high, I would not spend the extra money on a electronic ballast. The best standard ballast sold by Home Depot ($11.00) worked just as well as anything else in my tests.

One thing about electronic ballasts, when you turn the light on the lamps immediately illuminate, there is no flickering--very strange to see. Additionally, electronic ballasts should be totally silent, no hum.

Fixtures

The cheap shop light fixture that I was using did not even have a ballast that I could replace. It had a transformer, a capacitor and some other components at each end of the bulb. When I moved the GE Wide Spectrum Plant and Aquarium Light to Home Depot's best fixture, I was pleasantly surprised to find this doubled my light output. Thus, a good fixture makes a difference.

In the 1994 book "Threatened Cacti of Mexico" it is stated:

"Plants use light energy, but they need light of around 400 nm (Violet) and 700 nm (red) wavelengths, know as Photosynthetically Active Radiation (PAR)..... As already indicated, it is necessary to use lamps that produce sufficient PAR. The florescent tube lighting used for aquaria are suitable. Such tubes are long lasting (+/- 18,000 hours) and they work at their best between 20 and 30 C. If the intention is to obtain only germination and initial growth of seedlings prior to transplantation, it is enough to use only five florescent tubes per square meter. This number has to be doubled if plants are to be maintained under these conditions for a long time"

My growing area is about 1/2 square meter, and I have three, 4-foot fixtures (1220mm) for a total of six lamps. So I am a little over the recommendation (better to have more light than less). I have wrapped three sides of my growing shelf with reflective mylar to reflect light back into the growing area. All plants sit on a seed heating mat (about 85 to 90F (30 to 33C) as needed for germinatoin.

Suggested Reading

Articles

"Blooming Succulents under Fluorescent Lights" by Poincelot and Cunningham, in the USA Cactus and Succulent Journal Vol. XLVII Nov-Dec 1975, #6.

Web Links

How Fluorescent Lighting Works, Oct 1996, posting on The Krib

Creating a Low Cost Fluorescent Lighting System, article, Studo 1 Productions

Photosynthetically Active Radiation, (PAR) Wikipedia

This article was originally posted on the Yahoo.com Living Rocks Forum and is reproduced in edited form by permission of the author (registration may be required to access the original article).