by Ed Rosenthal
Cool white fluorescents emit more blue light than warm white. They are useful during the vegetative stage of marijuana growth because the blue light promotes stout, compact stem growth.
Fluorescents are three to four times more efficient than incandescent lights. For instance, you might see 20w fluorescents advertised as delivering the equivalent light output as a 75w bulb. The lamps they are being compared to are incandescents. But fluorescents are only 50-75% as efficient as high-pressure sodium (HPS) lamps. Even that comparison is not as exact as it seems because of other factors, including emitted light spectrums (some lights produce more PAR than others) and lamp placement requirements (cooler fluorescents can be kept closer to the canopy than hot HPS lamps).
Warm whites emit more red light than cool whites and are used during flowering because the red spectrum promotes flower growth. All of these lamps are readily available.
Several brands of special “Plant Growth” lamps are available. They concentrate their light emissions in the red and blue spectrums to provide plants with the more energy in wavelengths the chlorophyll can use. However, they produce less total light.
High Output (HO) fluorescents are supercharged fluorescents Use almost twice the power of standard fluorescent lamps. They can illuminate a garden very brightly and are an alternative light source to using a high-intensity discharge lamp. They are readily available in both T-5 and T-8 tube sizes. They make it a lot easier than adding more fluorescent fixtures to increase the intensity of light that gets to the plants.
T-8 STRAIGHT LENGTH TUBES
T-8 tubes are one-inch wide and come in lengths of 2, 4, 6, or 8 feet (0.6, 1.2, 1.8 or 2.4 m). They are typically mounted in standard reflectors. Conventional T-8 tubes use about eight watts per linear foot and produce approximately 650-700 lumens per foot (0.3 m). T-8 fluorescents emit about 15% more light per watt than T-12s. Their diameter makes it hard to place more than four of these tubes per foot (0.3 m), even without individual reflectors. Although reflectors maximize the light coming from each tube, it is difficult to place more than three per foot (0.3 m). These lamps are best suited for rooting clones and adding supplemental light to the garden. More useful are the HO T-8 fluorescents, which use about 12-14 watts per square foot (0.09 sq m) and produce 1,000-1,250 lumens per foot (0.3 m), so they can deliver more light to the plant.
T-5 STRAIGHT LENGTH TUBES
T-5 tubes are 5⁄8 inches (1.5 cm) wide and also come in a variety of lengths. A more recent introduction to North America, they use different ballasts and fixtures than the T-8 tubes. T-5 tubes emit almost 30% more light per watt than T-8s. Their more compact size means it is possible to fit four T-5 tubes in each foot of width. T-5 tubes are available in HO models, which are the ones usually sold in shops. A 4-foot HO tube uses 54 watts and emits roughly 5,000 lumens, almost twice as much output as a conventional T-5. A bank of eight, four-foot T-5 HO tubes emits 40,000 lumens and uses about 435 watts, as compared to a 400w HPS that actually uses 440w and produces about 50,000 lumens. Placed over a 4’x4’ area (16 sq ft or 1.5 sq m) the intensity is 2,500 foot-candles. T-5 HO fluorescents use about 60% more electricity than regular T-5s.
T-5 fluorescent lamps are very efficient sources of light. The tubes are thinner than other fluorescents, so they can be placed closer together. The reflectors have baffles that reflect the light so little is lost to the garden.
COMPACT FLUORESCENTS (CFLs)
Compact fluorescents are often the most convenient lamps to use in small gardens. Unlike other fluorescent bulbs, they have ballasts built into the bulb assembly, so they can screw into standard incandescent sockets. They are available as floodlights, twisted tubes, straight mini-tubes, and as 8- or 12-inch diameter circular fluorescent tubes. U-shaped screw-in fluorescents are also available. Another advantage of CFLs is that they deliver a lot of light from a small point. Unlike tube fluorescents that deliver their light over a large area, often spanning several feet, the compacts “point of light” emissions make it easier to increase light intensity by grouping them close to each other. Large-wattage CFL lamps are available in sizes of 25, 50, 100, 150, 200, and 250 watts.
The light emitted from CFL lamps is undirected. Since any light that doesn’t reach the plants is wasted, use reflectors to get the lights to the garden. Inexpensive clamp-on light fixtures with bowl reflectors and screw sockets make it easy to position the lamps.
To maintain a fast growing garden, a minimum of 30 watts of fluorescent light per square foot is required during the vegetative growth period. More light—up to 40-60 watts per square foot—produces more high-quality growth. As long as the plants’ other needs are met, the more light that the plants receive, the faster and bushier they will grow.
Compact fluorescents come in many wattages, up to about 200 watts. They’re not as efficient as HPS lamps, but are easier to set up.
You can use fluorescent lights in innovative ways to supplement the main source of light. Mixing light sources such as fluorescents or LEDs with High Intensity Discharge (HID) lamps helps the garden because together they provide more light and can fill in partially shaded areas. Fluorescent lights can be mounted along the sides of the garden or placed in the midst of it. Fluorescent light wands or work lights can be hung vertically in the midst of the garden or horizontally between rows. No reflector is needed for mid-garden applications, because the tube can shine on the plants from every angle.
Both fluorescent and LED lights should be placed about 2-10 inches from the tops of the plants. Don’t let the leaves touch them, because they will be burned.
Use bowl reflectors with CFLs.
CFLs emit the most light when they are positioned with the base up; base down they emit less. Horizontally placed lamps work least efficiently.
METAL HALIDE LAMPS (MH)
MH lamps are the type of lamp used outdoors to illuminate sports events because they emit a white light. They were originally promoted as the light to use during the vegetative stage of plant growth, before the plants are forced to flower. But now it is generally recognized that plants grow as well vegetatively under HPS lamps as under MH, so they are not used that much because they emit less total light than HPS lamps and produce lower yields.
MH lamps, like fluorescents, come in many spectrums. This is a very important factor in figuring how effective your lamp is. In general, 15% of the energy used by MH lamps is emitted as PAR, as compared with 13% for HPS. But the crisp white light emitted by standard MH lamps is low in the red spectrum. Since plants need red spectrum light for photosynthesis and flowering, its absence is felt. Nonetheless, under metal halides, plants grow quickly and flowering is profuse, with heavier budding than under fluorescents. The brighter light penetrates a bit deeper into the canopy.
These plants are growing well under high power CFL fluorescents. The fluorescents supply intense light to the garden producing much less heat than exotics.
MH lamps may be the solution to plant lighting problems indoors and out. These are ideal lights for a garden where the amber light spectrum of an HPS would be indiscreet. During the fall, metal halide lamps can be used in backyard gardens to supply the extra energy boost needed to ripen. Run the lights during the day to supplement the ambient light. Although the light they emit is very bright, it is white, not the unusual amber color emitted by HPS lamps, so it is not as likely to cause suspicion.
MH lamps come in 250-, 400- and 1000-watt sizes. The 250w lamp can light a garden 2’ x 2’ (60 x 60 cm). The 400w lamps can easily illuminate a small garden 3’ x 3’ (90 x 90 cm) or smaller. The 1000w lamp can illuminate a garden of about 4’ x 4’ (120 x 120 cm).
The lamps are convenient to use. The complete unit consists of a lamp (bulb), fixture (reflector) and long cord that plugs into a remote ballast. The fixture and lamp are lightweight and are easy to hang. A chain or rope is used to suspend the fixture, which takes up little space, making it easy to gain access to the garden.
ASK ED: Marijuana Questions
B
ROKEN METAL HALIDE BULB
I recently saw a warning about UV emissions. The author stated that if the protective glass around a metal halide were to break, you should unplug it immediately because without this glass, the metal halide would emit harmful levels of UV radiation. Since reading in your ASK ED book about increased UVB increasing the THC production, I have been looking for a good source of UVB supplementation. Have you ever heard of anyone removing the glass from a MH to increase UVB? How much increased UVB would you receive? Or, is it truly unsafe to do so?
It is unsafe to use a MH with a broken outer bulb. Not only does it emit large amounts of harmful UVB rays, which cause sunburns. It also releases UVC light, which is deadly to most life forms. Broken MH lamps are not something you want to tinker with.
METAL HALIDES & ULTRAVIOLET LIGHT (UV)
Ultraviolet (UV) light, as discussed above, is composed of spectrums beyond blue that are invisible to humans but are visible to many animals. UV light is divided into three bands—UVA, UVB, and UVC. UVB is critical to the development of THC. The potency of marijuana is dependant on the amount of UVB light it receives. Metal halides emit UV light and can be used for this purpose.
Even if plants are being grown under HPS lamps, potency—that is, THC content—will increase significantly if they are replaced with metal halides during the last two weeks of flowering. Just be aware that the protective glass in air-cooled MH fixtures absorbs UV light before it gets to your garden. So the only way to benefit from the UV output is to remove the glass and take other steps to cool the light.
HIGH PRESSURE SODIUM VAPOR LAMPS (HPS)
High-pressure sodium (HPS) vapor lamps emit an orange or amber-looking light. HPS lamps are commonly used as streetlights. Their spectrum is heavily concentrated in the yellow, orange, and red spectrums with only a small amount of blue. HPS lights are usually used for flowering because they supply more orange and red light than MH lamps. The increased red and yellow light seems to promote more flower production.
Gardeners usually use HPS sizes of 150, 250, 400, 600, 750 or 1000 watts, all of which are sold in indoor garden shops. They produce about 15% more light than MH and use the same configuration: lamp, reflector, and remote ballast. The 600- and 750w HPS lamps are about 7% more efficient than the other sizes.
Small watt HPS lamps are available in hardware stores. They are used for outdoor lighting. They can be used to light tiny gardens and for brightening shaded or dark areas of the garden or to extend the canopy when plants bush out.
Space HPS lamps so they provide an even light throughout the garden. Placing the lights about a meter (about 3’) apart provides an input of approximately 60 watts per sq ft (660 watts per sq m).
HPS lamps emit 13% of the energy they use as PAR. The 250w lamp can light a garden 2’ x 2’ (60 x 60 cm). The 400w lamps can easily illuminate a small garden 3’ x 3’ (90 x 90 cm) or smaller. The 600w lamp illuminates a garden about 3.5’ x 3.5’, the 1000w lamp can illuminate a garden of about 4’ x 4’ (120 x 120 cm).
HPS lamps support fast growth during both vegetative and flowering stages. They need no supplemental lighting during any stage of growth. HPS lamp brands and models differ in both the amount of light emitted per watt and in the spectrum that is emitted.
Some HPS lamps emit enhanced levels of blue light, which encourages stout short stems and branches. Since light of particular spectrum is processed differently by plants, some lamps produce more growth and flowering than others. For more about the differences between HPS bulbs, see the website for the results of our tests of many of the most popular brands.
ASK ED: Marijuana Questions
AGING HID LAMPS
How can I tell when a working HPS or metal halide bulb is ready for retirement? I’ve read that the bulbs emit less light over time. If the amount of light declines gradually, I might not notice the light decline. Should I mark the bulbs with the date I put them into service? How long do the bulbs last?
Lights become dimmer as they age. To check a lamp use a light meter or compare the old lamp with a new one. Bulbs should be replaced after about 8 or 9 months if they are being used for flowering, or after five months if the lamp is on continuously. Their light production diminishes with time and use.
Gardeners often combine HPS and MH lamps because they think blue light from the MH lamps keeps the stems stouter and shorter. But any benefit is likely to be far less than they would suppose. The red light of HPS lamps does not cause plants to stretch. Stretching is caused by far-red light, and HPS lamps don’t emit light in those wavelengths. Confusion about this stems from how similar the light from incandescent lamps and HPS lamps look. Both emit visible light primarily in the yellow, orange and red spectrums, so gardeners confuse the spectrums of the two lamps. But incandescent bulbs emit more far-red than visible light, and HPS lamps don’t.
BALLASTS
Each MH and HPS lamp has an electrical system that requires conversion to higher voltage than is delivered through the electrical grid. The ballast converts house current to the appropriate voltage. Ballasts used to power garden lights are usually remote from the light, connected by a long electrical cord. The convenience of this is that the heavy ballasts are not hanging from the ceiling, only the much lighter and less cumbersome reflector and bulb are stationed above the plant canopy.
Old-style magnetic ballasts are dedicated to a particular type and watt lamp and a single grid voltage, such as 110 or 220. Most digital ballasts can be used for both MH and HPS lamps of the same wattage and can be used with both 110 and 220 voltage. Some can power different wattage lamps.
Digital ballasts are the most efficient way to power indoor lights. Quantium Ballasts are equipped with a dimmer switch that allows the grower to regulate the energy output and intensity of the lights. Lamps powered by digital ballasts emit 15-20% more light than a standard electromagnetic core ballast.
Compared to magnetic ballasts, digital ballasts are more convenient to use for several other reasons:
•Magnetic ballasts use 20% more electricity than the bulb is rated to convert the electricity to an appropriate form. Digital ballasts use about 10%, half the current of a magnetic. As a result a 1000w lamp and magnetic ballast consume 1,200+ watts.
•Magnetic ballasts contain an iron magnetic core so they are heavy. A ballast for a 1000w lamp weighs between 35 lbs (16 kg) (MH), 44 lbs (20 kg) (HPS), and up to 54 lbs (24.5 kg) for a MH/HPS convertible unit. Digital ballasts weigh much less, only 8-12 lbs and most often ignite both MH and HPS bulbs.
•All magnetic ballasts hum. Digital ballasts are silent.
•Digital ballasts are gentler on the bulb during start-up.
•Digital ballasts regulate currency more precisely. The bulb receives a more even electrical flow so it is stressed less. It lasts longer, emits a brighter light, and doesn’t flicker.
•Digital ballasts are “smart”. They recognize the type and size of bulb that they are powering, so a single ballast can be used for either a HPS or MH bulb.
•Digital ballasts turn themselves off if they encounter any kind of problem.
•Magnetic ballasts emit a lot of heat. Digital ballasts produce a lot less.
•Digital ballasts are more expensive than magnetic ballasts, but they save electricity, labor, and effort while producing more light, resulting in more bud.
Digital ballasts have many advantages over electromagenetic ballasts, they are quieter and more efficient, and operate at a higher frequency, minimizing the wear and increasing lamp life. The Global Greenhouse Ballast is lightweight, creates very little heat, and works with both MH and HPS lamps.
LED LIGHTS
The latest addition to indoor lighting options is lamps made from Light Emitting Diodes (LEDs). LEDs come in many configurations, including flood lights, panels, bars, circles, and rectangular fixtures. LEDs create little heat, and fixtures are only three or four inches deep, so they make great lamps for closet cultivation or other spaces where height is an issue. LEDs ar
e also highly efficient, using less electricity than HIDs and even fluorescents.
LEDs are unique among lighting systems because each diode emits light in an unusually narrow spectrum. The minerals used to make it determine the spectrum the diode emits. HID lamps emit most of their light in spectrums that are not very useful to the plant. With LEDs, fixtures can be designed to provide the plants with exactly the spectrum that they need for maximum growth.
LED lights emit light in a narrow portion of the light spectrum. Light output is concentrated in the light bands that plants use most efficiently, red and blue. The Supernova LED by HidHut features adjustable lighting controls that allow the grower to determine the ratio of blue to red light it projects. Fans are built into the equipment so very little heat is produced.
LEDs emit very little heat and can be placed very close to the plants. The light spreads at a 120° angle. This LED from Maxx Power has a built in digital driver that monitors the power going to the bulbs 100 times a second and adjusts accordingly to ensure that maximum output is being achieved.
By tailoring the diodes’ light spectrum to plant requirements, LEDs can be more efficient PAR producers. HPS lamps deliver more total light per watt of input, but LEDs are twice as efficient in PAR light per watt as HPS lamps. That means a 200w LED lamp can be substituted for a 400w HPS lamp, and the 300w LED lamps can be substituted for 600w HPS lamps. The first generations of LED lamps did not emit an intense-enough light to support either active vegetative growth or flowering, but modern fixtures, which use higher-capacity diodes, have solved those early problems.