New Technology and Techniques for Indoor Plant Growing: Part One
by Bill Lermer
Light Spectrum
The factors of growing plants are interdependent and synergistic. The most important of these is light. Growers should start by getting the best possible light their budget can afford. What light is best, depends on the space and situation available. The following techniques are valid for just about any vegetable or herb, such as tomatoes and basil.
Conventional wisdom dictates that the growth phase be illuminated by a quartz metal halide (for blue light), the bloom phase by a high pressure sodium (for yellow/orange light). However, a full spectrum is needed for all phases for a variety of functions. Blue induces growth hormones and rooting and reduces stem elongation. Red induces flowering hormones, and provides energy for growth of flowers and leaves. Using only quartz halide during growth phase results in slow growth due to less red light. Using only hps light during the flowering stage often causes leaf yellowing, (due to lack of growth hormones) and often causes stem elongation.
Red light is the most efficient monochromatic spectrum for plant growth. However, all the colors have functions. If a person were especially good at hearing bass sound, that means the other pitches should be emphasized, so that you can hear the whole melody. For light to be efficient for plant growth, it must be full spectrum with close to equal linearity and amplitude through the production of 400-700 nm, with a slight bump in the red.
The best widely available full spectrum light is called “Ceramic Metal Halide” or “High Pressure Metal Halide”. This has more blue than a quartz halide, and more red than an HPS, so it’s the best for all stages. The far blue range includes UV-B, similar to what is found at high altitudes, and increases the prized phenolic compounds. This increases the potency and flavor of peppermint, licorice, pepper, etc. The Ceramic Metal Halide (CMH) features a ceramic arc tube like an HPS, and uses an HPS or electronic ballast.The CMH is superior to the retro-fit HPS that operates on a MH ballast. The retro-HPS is more expensive, lasts only half as long as a regular HPS, has reduced output, and the spectrum isn’t as good as CMH. The retro-quartz-halide that operates on an HPS ballast is very inefficient.
A mixture of halide and sodium is sometimes recommended. Mixing the two different light sources is difficult unless the horizontal orientation is used, and even then, the light under the halide is more halide (and the light under the HPS is more HPS). Halide and HPS light waves are out of phase with each other, and like oil and water, don’t fully blend together. The quartz metal halide doesn’t operate very well horizontally, the light is less total, doesn’t reflect as well and bulb life is shortened. However, quartz halide and hps can be blended by having both in the same reflector and spinning the reflector.
Light Distribution
Around the edge of a cluster of horizontal lights is weak diagonal lighting; this can be compensated for by 100w side lights. If a single horizontal light were used, non-uniform growth would result from the non-uniform distribution of light. For a single light, a paraboloid reflector would give uniform distribution of lighting. However, a cluster of full spectrum horizontal lights is the best:
- Full spectrum light sources would be in phase with each other
- Light directly from the bulb has more energy than reflected light
- Overlapping of light patterns
- increases total light due to the array effect (that’s why chandeliers have many instead of one big candle)
- allows for sufficient light in fringe areas, at edges of most light footprints
- increases diffusion because light comes from different angles; this increases reception of light by the leaf surface.
A horizontal 400w CMH full spectrum light, with a horizontal paraboloid diffuse reflector, covers about a three foot x four foot oval area by itself. When combined in a cluster, each such light covers about a four foot x five foot area. This is because outside the three foot x four foot area of high intensity, there is a fringe area of lesser intensity. When the fringe areas overlap, they become high intensity areas.
The highest reflective surface is 98% reflective, and this is specular or mirror-like. The specularity reflects light at exact angles, like the edges of a pool table. This has the disadvantage of creating hotspots (unless the angles are very well-designed and precisely shaped, as in a four foot parabolic reflector). The lack of diffusion or multiple angles of light rays can create shadows on the leaf surface.
The leaf receives better when light is coming from different angles, so I recommend the bulb be oriented horizontally, with a diffuse reflective surface. When horizontal lights are in a cluster, the different angles of light increase diffusion. White is diffused, and the best white paint is about 90% reflective. Glossy white is only 68% reflective. Some types of flat white can’t always be cleaned, but can be repainted. Silver reflective surfaces are normally specular, but there is a 97% reflective silver that has micro indentations for diffusion.
Electronic Ballasts
Electronic ballasts are more efficient than magnetic, and also improve bulb life and efficiency.
Be sure to get an e-ballast that is protected against electromagnetic interference (emi). Life Lights is protected against emi, as required by FCC regulations, and is German VDE-listed.
The electronic ballast also improves the spectrum; the spikes are smoothed out. CMH, whether powered by electronic or magnetic ballasts, is a full spectrum light - the best for SAD (seasonal affective disorder) or horticultural applications.
Different E-Ballasts such as Life Lights
- have long-range ignitors (up to 90’); magnetic ballasts typically have short-range ignitors (up to five feet); and most e-ballasts are only rated for 12’ of lamp wire.
- have 6KV pulse-rated wire and quick disconnect connectors, including a ground wire. Others may have only two bare non-pulse-rated wires sticking out of the ballast enclosure (with no strain relief), or have connectors that could melt.
- had only two percent failure rate in VDE destructive halt tests, and had a 0% failure rate in tests of normal operation done by BC Hydro Power.
- have US patents for their advanced technology.
- are sealed, and cooling fans pull air by the heat sink instead of the delicate circuits. If not sealed, the circuit would accumulate dust and moisture.
- have a high frequency carrier wave, not detected by power company detectors. This high frequency simulates natural sunlight, leading to greater absorption of light by the leaf.
- have three indicator lights to tell if the bulb needs to be replaced or if the lights are dimmed. During cloud cover (in a greenhouse), lights would be at full intensity; if the room were too hot, the lights would be dimmed.
- are micro-processor-controlled, to adapt quickly to changing circuit conditions, and allow for dimming.
Limit the growth phase to 10” [25.4 centimeters] in height, and use the continuous (as opposed to simultaneous) method. The continuous method employs one veg light for every four bloom lights, on rotation.
The short height will reduce the time spent on growth, and increase light levels on the lower leaves. If the plant is only 10” - 12” [25.4 - 30.48 cent] when it goes into bloom, it will grow another 1’ - 1 1/5’ [.3048 -.4572 cent] in the bloom phase--the maximum height (2’ - 2.5’ ) [.6096 - .762 meter] that can be adequately covered with efficient lighting.
If the container (e.g. Classic 1400) or hydro bucket is 10.5” [26.67 centimeters] wide, 12 plants can be placed one next to the other under a four foot [1.2192 meter] parabolic reflector with 400w CMH, the same number that can be placed in the bloom room with four inch [10.16 centimeters] spacing in between buckets. The four inch spacing isn’t needed in the growth phase if vertical height is limited to about 10” [25.4 centimeters], since the plant is usually taller than it is wide. The plant will approximate the shape of the container, so the container should be wider than it is tall. Once they reach 10” [25.4 cent] tall, place them under the bloom lights. These should be of higher intensity, because the plant is taller and will need the intensity to cover the lower leaves.