High-Performance Garden Lighting (Part Two)
By Richard Tamassy
In last month’s article, High-Performance Garden Lighting we covered the history, electrical theory and some common modern horticultural applications of metal-halide (MH), high-pressure sodium (HPS) and compact-fluorescent (CFL) lighting technology.
The focus of this months article is how and where to practically apply what we have learned about lighting in order to design the most effective garden lighting environment possible for your crop.
Lighting Issues:
As far as your plants are concerned light is another form of food. Just like regular plant food, with its balance of nitrogen, phosphorus, potassium and trace elements that are necessary for the healthy development of each specific crop. Light, in different color mixes (spectra) is correspondingly necessary for the healthy development of each specific crop. Both must be applied at the correct times, for a specific amount of time, and in the correct amounts in order to contribute to the ideal growing environment for your plants and to make a crop flourish. With fertilizers, the quantities of each required element are well known and relatively simple to control in order to achieve optimum growth. However, when one is growing under artificial lighting, there is always a tradeoff between the limits of lamp technology, power and the ideal spectrum necessary to promote optimum growth and yield.
Unfortunately for plants, much of the lighting technology developed is designed to produce the maximum amount of human usable light energy (lumens) in stadium (MH lamps) and street lighting (HPS lamps). As Murphy’s Law would have it, plants “see” pretty much the opposite spectral curve of what the human eye sees. Which means that in reality, most of the electrical energy that goes into producing those visibly bright lumens is lost in terms of plant grow power. Fig 1 demonstrates how radically different the average plant spectral response cure is from that of the human eye.
Plant vs. Human Lighting Needs:
What the eye sees:
Human vision is most sensitive in the green region of the light spectrum. The in-depth scientific application of this is beyond the focus of this article, but the green light bias of the human eye has to do with the arrangement and bio-physical properties of the of the light receptors (namely rods and cones) in the eye itself. A practical example of this green light bias in real terms is military night vision. Night vision devices emit a specific shade of green not to be cool or cute, but because this particular green provides the best visibility to the human eye and appears the brightest of all colors of the visible light spectrum all things being equal. This peaked sensitivity provides the maximum visibility for objects viewed through night vision goggles and scopes. For plants, exactly the opposite is true.
Plants and Light:
Plants have leaves that are generally green. Technically, this means that plants reflect much of the available green light back into their direct environment, and this is why they look green. In simple terms, this means that plants are least sensitive to green spectrum light. So, what appears to be the brightest light to the human eye that has a bias towards green spectrum light may actually be very dim light in terms of plant grow-power. Don’t believe this… a couple of new products on the market use this phenomenon. All horticulturalists understand that it is absolutely critical to maintain complete visible darkness during the crops ‘off cycle” in order to maximize yield. Which means that most of the maintenance work has to done when the lights are on in order to avoid “awakening” the plants and interrupting the standardized 12-hour bloom cycle. As of late, a new series of green bulbs and green LED flashlights have been introduced into the market that allows gardeners to maintain their crop without disturbing the plants. The reasoning behind these products is pretty much an extension of what we have covered here; plants are least sensitive to green light, this is why they are not disturbed while the human eye is most sensitive to green light, this is why gardeners can see what they are doing even with such “dim” lighting. As the plant photosynthetic curve (PAR curve), shown in Figure 1 illustrates, of all visible light spectra, plants need blue and red light the most and green the least.
Measuring Lighting “Grow Power”:
Photosynthetically Active Radiation (PAR) is the basic standard measure for grow light efficacy. This light measurement system uses a spectral curve that is similar to the one shown in Figure 1 as a Standard. Commercial horticultural lighting manufacturers generally express the PAR system in terms of PAR Watts, thereby providing an simple means of comparing the available “food value” that your plants can utilize to grow. PAR Watts also provides an easy way of comparing different brands and varieties of HPS and MH lights for the amount of plant grow power.
However, plant photosynthesis involves four different pigments that convert the light energy into plant usable energy. Simply put, each specific pigment responds to specific spectra of light. The average response for all the pigments is shown in the PAR curve. The relationships between the amounts of activation of each specific pigment have also been shown to cause physical changes in plant development and physiology. The blue end of the spectrum appears to be predominantly responsible for elongation and green growth development while the red end of the spectrum has been shown to increase fruit development. Figure 2 provides a graphic summary of this.
In the modern high-yield garden, this is commonly applied. Blue light sources, such as MH and cold (6,400K+) CFL’s are used for the vegetative stage where the plant builds its green growth and root foundation. While red light sources, namely HPS and warm (2,700K) CFL’s are used in the bloom or fruiting stage in order to focus the plants energy on building the largest fruit size and quality. These are the tricks that gardeners use in order to generally compensate for the less than ideal spectrum provided by commonly available HID lights.
About CFL’s:
CFL’s are the only singular lights currently available that can be specifically tailored to ideally match the PAR curve. The CFL uses a phosphor coating to convert its internal UV light into visible light spectrum. If the coating is altered, the light spectrum is directly altered. It is a relatively simple matter to “dial-in” the ideal PAR curve spectrum by applying the proper phosphor coatings. Additionally, unlike MH or HPS lights, multi-phosphor (properly designed) CFL’s emit a much broader and smoother spectral curve than the typically peaky narrow spectrum produced by commercially available HID lights.
I understand that some readers have a very strong dislike for CFL lighting technology, and from the way CFL’s have been marketed to the gardening community in the past, this is understandable. However, that being said, CFL’s are ideal for spectral supplementation (not replacement) to HPS lights. We have fielded a number of reports where gardeners were using 1,000 watt MH bulbs for vegetative growth. Based on the broader spectrum offered by the 6,400K CFL, they replaced the 1,000 watt MH until an equal level of vegetative growth was achieved over an equal period of time. In these independently run tests, it took three 125 watt 6,400K side-light blue CFL’s (375 watts combined draw) to replace one 1,000 watt MH. Although, we do not recommend CFL’s as direct replacements for HID lights, especially in the bloom stage, these informal tests do illustrate how much can be gained from a light source that has a broader and fuller spectrum than traditional HID lighting.
This is why we feel very strongly about supplementing the red spectrum of HPS lights with a properly installed, good quality, multi-phosphor blue spectrum CFL. The gains in photosynthetic efficacy, plant health, and yield are well worth the relatively small extra investment. Figure 3 depicts the spectral output of a commonly used, name brand 1000W HPS light alone and when used in conjunction with our side-light blue CFL’s placed inside of our Pro-Gro 1250 vented hood. The increase in essential near UV and blue light is obvious.
Simply put, your plants see light as another food source, i.e. not much different from fertilizer, all the CFL is doing is adding the missing “trace-elements” necessary to achieve maximum potential from your crop. It’s pretty simple.
Sample Garden Applications:
The following illustrations provide an example for building a “dream” garden without having to go through all the calculations necessary to obtain ideal lighting values in a set room size. The space occupied by the garden is 12 feet by 12 feet by approximately seven to eight feet tall. In future articles, this is the standard garden that will serve as a reference to illustrate different concepts and techniques. In all instances, it is recommended that the garden walls be lined with silvered Mylar or similar reflective material in order to maximize on the available light produced by the grow lights. In all instances, it is also recommend that HPS lights are used in conjunction with properly designed blue spectrum CFL’s in order to maximize the plants photosynthetic capabilities and deliver the best possible plant health and fruit yield. However, should you choose to make your own reflectors, tests have shown that the individual constructor use one reflector for the main HPS bulb and one separate reflector for the CFL bulbs at each bulb site with an approximate ratio of 500 watts of HPS to 125 watts of blue CFL. Even if the gardener chooses not to go with the mixed spectrum concept at all, these examples should still prove as a useful basis for further development.
Figure 4: The 4-By Soiless
General Notes:
- Five gallon bag or rigid plant pots
- Vegetative growth cycle
a. Move plants to one side of room so that they can be veged under two lights in order to conserve power
b. Use two 1,000 watt MH conversion bulbs or
c. Use a balanced spectrum hood featuring a 1000 watt HPS plus two side-light blue CFL’s
d. Set light on cycle to approximately 18 hours - this appears to be the optimum average for different plant verities
e. Vegetative cycle time will vary from 1.5 to three weeks depending upon plant variety, environment and fertilizer - Bloom (fruiting) cycle
a. Distribute plants evenly throughout room
b. Replace the two currently installed 1,000 watt MH conversion bulbs with 1,000 watt HPS main lights or
c. If you are using the Pro-Gro 1250’s, step “b.” is unnecessary
d. Plug-in remaining two reflectors, so that all four reflectors are operational
e. Set light on cycle for approximately 12 hours - this appears to be the optimum average for different plant verities
f. During the bloom cycle, it is absolutely imperative that no light is allowed to enter the room when the main lights are off. If light enters, you will get reduced yield and potentially obtain no fruit at all under extreme instances
General Notes:
- Select your favored method of growing. Flat-table can be configured for soiless, hydroponic flood-drain, aeroponic, constant drip, deep-water culture etc.
- Vegetative growth cycle
a. Depending on the growing method you have selected, you may be able to utilize one table for the vegetative cycle by moving the plants onto this one active table
b. Use 1,000 watt MH conversion bulbs or
c. Use a balanced spectrum hood featuring a 1000 watt HPS plus two side-light blue CFL’s
d. Set light on cycle to approximately 18 hours - this appears to be the optimum average for different plant verities
e. Vegetative cycle time will vary from one to six days depending upon plant variety, number of plants, environment and fertilizer - Bloom (fruiting) cycle
a. Distribute plants evenly on flat-tables
b. Replace any currently installed 1000 watt MH conversion bulbs with 1000 watt HPS main lights or
c. If you are using the pro-gro 1250’s, step “b.” is unnecessary
d. Plug-in remaining two reflectors, so that all four reflectors are operational
e. Set light on cycle for approximately 12 hours - this appears to be the optimum average for different plant verities
f. During the bloom cycle, it is absolutely imperative that no light is allowed to enter the room when the main lights are off. If light enters, you will get reduced yield and potentially obtain no fruit at all under extreme instances
Same general instructions that apply to the 4-By Soiless garden also apply here. The concept of 3-D side-lighting is to enhance crop yield and quality by providing increased lighting to the lower regions of the plant and further light spectrum enhancements.
Please Note: These diagrams are intended strictly for academic purposes only. The diagrams do not constitute actual plans and as such are not formally approved for construction or approved to meet building, electrical or fire and safety codes. If you have any specific questions, please refer to a qualified professional.
Summary:
Thank you for staying with us. This concludes the High-Performance Garden Lighting series.
In the next issue of Maximum Yield magazine, we will cover the very unique topic of Safety and Security.
Richard Tamassy is CEO of Broad-Leaf Grow Gear Inc. and heads up the product design team