Fluorescent Lamps

Marijuana Horticulture

by Jorge Cervantes

Fluorescent lamps have gone through major changes in recent years. New bulbs produce more light. Most growers use fluorescents to grow clones and small vegetative plants and maintain mother plants. Some growers even use them t flower a crop. Fluorescents are available in many different spectrums, some almost identical t natural sunlight.

Flurescent lamps are long glass tubes that come in a wide variety f lengths, from one to twelve feet. The two- and four-foot tubes are the easiest to handle and most readily available. Two four-foot fluorescent bulbs in a shop light fixture cost from $20 to $30.

Fluorescent lamps work very well for root cuttings. They supply col, diffused light in the proper color spectrum to promote root growth. Use any daylight spectrum fluorescent lamp to root cuttings. Fluorescents produce much less light than HIDs and must be very close (two to four inches) to the plants for best results.

Using fluorescents along with HIDs is awkward and problematic. When using them in conjunction with HIDs, fluorescents must be very close to plants to provide enough intense light to do any good. Fixtures may also shade plants from HID light and generally get in the way.

Plants will flower under fluorescent lights. The buds will be small and light, but, with enough fluorescent light, you can grow a mature crop. The grow show will have to literally be lined with fluorescents.

Fluorescent tubes are available in so many different wattages or outputs that they are hard to track! All fluorescents require specific ballasts. The old standard (T12) tubes use about 10 watts per linear foot. A two-foot tube uses about 20 watts, fur-foot: 40 watts, etc. The most common bulbs used for growing are available in lengths from 15 inches to four feet. lamps are available in very low to more than 50 watts. Circular fluorescent tubes are available but used by a few growers.

Power twist, or groove type, lamps offer additional lumens in the same amount of linear space. The deep wide grooves give more glass surface area and more light output. Several companies market variations of power twist fluorescents.

Black light fluorescent lamps emit ultraviolet (UV) rays through a dark filter glass bulb, but they are not used to grow cannabis. Ultraviolet light is supposed to promote more resin formation on the buds. However, all known experiments that add artificial UV light in a controlled environment have proven that it does not make any difference.

Most of the major lighting manufacturers – GE, Osram / Sylvania, and Philips – make fluorescent lamps in a variety of spectrums. The most common are Warm White, White, Cool White, Full Spectrum, and Daylight. Sylvania has the Growlux and the Wide Spectrum GroLux. The Standard GroLux is the lamp to use for starting clones or seedlings. It is designed for use as the only light source, having the full spectrum necessary for photosynthesis and chlorophyll production. The Wide Spectrum GroLux is designed to supplement natural light and covers the blue to far-red regions. Westinghouse has the AgroLight that produces a very similar spectrum to the sun. Warm White and Cool White bulbs used together make excellent lamps to root clones.

Fluorescent bulbs are further classified by diameter and come in the sizes T12 (1.5 inch), T8 (1 inch), T5 (0.625 inch), and CFL. The T12 uses old fashioned magnetic ballasts. The T8 and the T5 (technically CFLs) use electronic ballasts. Growers prefer slimmer T8 and T5 bulbs with electronic ballasts because they run cooler, electricity cycles faster, and lights do not flicker.

Construction and Operation

Fluorescent lamps create light by passing electricity through gaseous vapor under low pressure. Like the HID family, fluorescents require an appropriate fixture containing a small ballast to regulate electricity and household electrical current. The fixture is usually integrated into the reflective hood. There are several types of fixtures. The most common fluorescent bulbs used for growing are hooked to sockets with bi-pin connectors. If purchasing new tubes, make sure the bulb fits the fixture. The fixture may contain one, two, or fur tubes.

A ballast radiates almost all heat produced by the system. The ballast is located far enough away from the fluorescent tubes that plants can actually touch them without being burned.

Ballasts will normally last 10-12 years. Used fluorescent fixtures are generally acceptable. The end of a magnetic ballast’s life is usually accompanied by smoke and a miserable chemical odor. Electronic ballasts simply stop. When the ballast burns out, remove it and buy a new one to replace it. Be very careful if the ballast has brown slime r sludge on or around it. This sludge can contain carcinogenic PCBs. If the ballast contains the sludge, dispose of it in an approved location. Most modern fluorescents are self starting, but older fluorescents require a special starter. This starter may be integrated into the body of the fixture and hidden from view, or be a small metal tube, located at the end of the fixture on the underside. The latter starters are replaceable, while the former require a trip to the electrical store.

If your fluorescent fixture does not work, and you are not well versed in fluorescent troubleshooting, take it to the nearest electric store and ask for advice. Make sure they test each component and tell you why it should be replaced. It might be less expensive to buy a new fixture.

The tubular glass bulb is coated on the inside with phosphor. The mix f phosphorescent chemicals in the coating and the gases contained within determine the spectrum of colors emitted by the lamp. Electricity arcs between the two electrodes located at each end of the tube, stimulating the phosphor to emit light energy. The light emission is strongest near the center of the tube and somewhat less at the ends. If rooting just a few cuttings, place them under the center of the fixture for best results.

Once the fluorescent is turned on, it will take a few seconds for the bulb to warm up before an arc can be struck through the tube. Fluorescents blacken with age, losing intensity. Replace bulbs when they reach 70 percent of their stated service life listed on the package or label. A flickering light is about to burn out and should be replaced. Life expectancy ranges from 9000 hours (15 months at 18 hours daily operation).