Lights & Loops

Lights & Loops

INTRODUCTION
- preface
- why lights
- numbers, explained
- quality of light
QUALIFICATION
- grow vs bloom lights
- fluorescents
- HID lighting
- LEDs
- exotic gas lamps
QUANTIFICATION
- light density
- light uniformity
OPTIMIZATION
- why?
- reflective material
- reflectors
- structural optimization
LOOPS
- closed loop
- open loop
CONCLUSIONS
- combination & alternatives
- conclusion

INTRODUCTION
Preface
"Everything should be made as simple as possible, but not simpler."
-Albert Einstein

This is the absolute simplest way in which Plant Lighting can accurately and thoroughly be explained. If you don't have a basic physics/biology foundation, expect to read slowly, look things up, and be slightly confused. Welcome to life in the twenty-first century.

Why Lights
If you want to garden where there isn't Sun, you need something that produces similar radiation so the Plant can perform photosynthesis and thrive. Aside from this primary reason, some Plants display photoperiodism, meaning that they shift from a vegetative growth cycle to a flowering cycle based on photoperiod, or day:night (light:dark) interval. To propel growth and perpetuate internal Plant cycles, we need lights.

Numbers, Explained
People love to throw around various optics/photometry-related metrics when talking about lights. Obviously we all know exactly what we're talking about, but just for the sake of thoroughness:

Lumen (lm)- "luminous flux". Simpler version: how "bright" the light appears to the human eye. Because the human eye and the Plant don't use the same parts of the light spectrum (we'll get into this in a little bit), lumens aren't a particularly effective way of evaluating Plant lighting.

Illuminance (lm/sq.m, lm/sq.ft)- Lumens are the most common provided measure of light production, so we use this unit to talk (in laymen's terms) about the "density" of the light; basically the amount (lumens) per area of space (square foot or square meter). One Lumen per square meter is called a Lux. One Lumen per square foot is called a foot-candle. Cool.

Electromagnetic Spectrum- The range of all possible wavelengths or colors of light organized from low to high wavelength, starting with stuff we don't care about, to Ultra-Violet, through ROYGBIV (figure it out) and on to Infra-Red and more stuff we don't care about. We talk about a specific point or color on this spectrum using the corresponding nanometer length of the light wave in question.

Absorption Spectrum- For a light-absorbing thing (like a Plant), a graph showing the relative amounts of light absorbed at different all different wavelengths along the electromagnetic spectrum.

Radiation Spectrum- For a light-producing thing (like a lamp), a graph showing the relative amounts of light produced at all different wavelengths along the electromagnetic spectrum.

Photosynthetically Active Radiation (PAR)- The band of the EM Spectrum from 400nm-700nm wavelength, as an approximation of the photosynthetic absorption spectrum.

Photosynthetic Absorption Spectrum- The absorption spectrum of the specific agents that fuel photosynthesis (again, to oversimplify). In other words, the relative amounts of various wavelength light along the EM spectrum that Plants actually use to grow.

Quality of Light
By comparing the Radiation Spectrum of a particular lamp with the Photosynthetic Absorption Spectrum, we can determine how effective a light will be in fueling photosynthesis. Unused Light (outside the photosynthetic absorption spectrum) doesn't aid in Plant growth and still produces radiant heat on the Plant. Therefore, matching lights to the Photosynthetic Absorption Spectrum is crucial for productive growth and low-to-canopy light height. Lumens don't mean diddles except as some general rule-of-thumb for how much light is produced. PAR is an approximation, and not even a particularly good one. Anyone who tries to use a single metric to claim one light is better than another is lying to you. I also am probably lying to you. That's what you get for reading things on the Internet.

QUALIFICATION- Differentiating between types of lights
Explaining the great mystery of Grow Lights vs Bloom Lights
Most Plants grow better if a blue-dominant bulb is used for vegetative growth and a red-dominant bulb is used for flowering (barring a few full-spectrum LEDs and exotic gas lamps). But if the Sun produces basically the same spectrum year-round (it does) and the photosynthetic absorption spectrum never changes, why on Earth would you need two different kinds of lights? I have never been able to find anyone with a worthwhile explanation for this phenomenon. Except for myself. My explanation is awesome: The blue-for-veg, red-for-flowering distinction exists because photosynthesis isn't the only thing that uses light in the Plant. "Photoreceptor proteins" are basically sensors for particular kinds of light that exist naturally in both plants and animals. We have them in our eyeballs to sense the absence of light and help trigger sleep when our eyelids close. A particular photoreceptor in Plants called Phytochrome only likes red and far-red light and it controls, among other things, Photoperiodism (the switch from vegetative growth to flowering). The presence of more red and far-red light in HPS Lamps/2900K Fluoros/other "bloom" lights explains why they are necessary for Flowering, in that the mostly-blue veg lights lack enough red and far-red light to sufficiently trigger Phytochrome and initiate flowering response in the Plant. The blue-light Metal Halides/6500Ks/ other "grow" lights feed a few different blue light photoreceptors that control other plant functions like Phototropism (look it up). Lights that cover the entire spectrum thoroughly, like some LEDs, Plasmas, and Magnetic Induction Lamps, and the Sun, work for both cycles because they provide for photosynthesis and all the photoreceptors. Science. What a thing.

Fluorescents
In a fluorescent lamp, electrical current runs through a phosphorus-coated tube of mercury vapor, causing it to "glow" and produce light. The actual process is more complicated than this (obviously), but we aren't here to design and build our own gas tubes. "Fluoros" are sold in different lengths (usually 2 or 4 feet long) and also different sizes (thickness i.e. tube diameter). The T5, T8, T12 etc. distinction basically just tells you size. CFL stands for Compact Fluorescent Lamp, wherein the bulb plugs in to an incandescent-type socket, instead of its own special fixture. These are limited in size because the ballast (a device that regulates the amount of electricity running through the bulb so it doesn't explode) has to be a part of the bulb plug, as opposed to being built into the fixture (as it is with a T5/T8/whatever-type tube Fluoros). Bulbs are rated based on their "color temperature", expressed in X,XXX K, or thousands of degrees kelvin. Without getting into the idea of blackbody radiation (which explains this nomenclature but doesn't do much else for us), we can simply realize that 2900K bulbs produce relatively more light on the red side of the visible spectrum, suiting them to flowering growth cycles, and 6,500Ks produce more blue-side light, suiting them to vegetative growth. Fluorescents are relatively efficient, at least compared to incandescent bulbs, and some growers truly swear by their effectiveness in terms of quality production. However, in order to get ample light density in your growing area, lots of bulbs are necessary and they must be very close to the plant canopy.

HIDs
HID stands for High-Intensity Discharge, a lighting tech that works by running current through Gas (like a Fluoro) and Salt (not anymore), causing the plasma in the arc tube to light up in a serious way. It has been surmised that, upon having had relatively mediocre luck with conventional incandescents, some unknowingly genius hippie jacked a streetlight and struck photosynthetically active gold sometime in the 60s or 70s. Who knows? Anyhow, we name the bulbs based on the stuff inside, and while there are a bunch of different kinds in existence, there are two in particular that have been found to work well for growing Plants: High Pressure Sodium (HPS) and Metal Halide (MH) lamps. Like Fluorescents, HIDs require ballasts, but in this case the ballast is bulky, complicated, and hot enough to warrant (typically) being a separate component. Spectra aside, years of use show that HIDs work pretty darn well for growing plants. They produce considerable heat, but any amply powerful lighting system will require an air-cooling system of some sort (see Loops). HIDs' widespread use in many types of lighting means that they've been extensively developed, have particular spectra based on the desires of their producer, and are relatively cheap and robust. Watt-for-watt, when used properly, HIDs are a potent way to facilitate plant growth.

LEDs- Solid State Lighting
Light emitting diodes run current through a tiny chunk of solid/powdered material(s) that glow at particular band of relatively few wavelengths. By combining various quantities of different wavelength-band LEDs, almost any radiation spectrum can be created. Unlike gas lamps, where plasma generates an entire spectrum, each LED emits a very limited number of light wavelengths. The effectiveness of an LED grow light depends entirely on the competency of the manufacturer to create the right radiation spectrum by choosing the specific numbers of different wavelength LEDs. In comparison to basically anything else, LEDs are far superior in terms of both use-life and efficiency. They will probably become the dominant source of Plant lighting as time progresses, but for a variety of reasons, haven't achieved this yet. As usual, looking at the radiation spectrum of the lamp in comparison to the photosynthetic absorption spectrum of the Plant gives a reliable indication of how effectively the light will facilitate growth.

Gas Exotics- Plasma & Magnetic Induction
Plasma lights are chambers of mixed gasses excited by RF (radio frequency) waves. Nice spectrum, relatively cool, but very expensive and therefore relatively uncommon. They also aren't particularly efficient in terms of light output relative to energy consumption, so it's doubtful that these lights will gain any sort of mass popularity. For a discerning professional looking for a very specific set of advantages, however, they definitely serve a purpose.
Magnetic induction lamps produce light using a mechanism similar to that of Fluorescents. However, instead of the current running through a bulb via metal filaments at either end, it (current) is created using an electromagnet outside of the gas chamber. Because of this indirect approach, these lights deteriorate incredibly slowly and, if built correctly, can produce a radiation spectrum that works well for plants in all stages of growth. Currently they're quite expensive as an up-front cost but their efficiency and long life make them worth considering in some situations.

QUANTIFICATION- how big/how high/how many
Light Density
While lumens kind of suck, they are the common measure of "quantity of light" that most lamps are rated with, so we have to use them anyway (at least for the time being). Ideal Light Density is the "amount" of light (number of lumens) that you want per area of canopy space that is being considered (square feet, square meters, etc.). For full-sun Plants this can be estimated by the generally accepted measure of light density that full outdoor Sunlight provides: 100,000 Lux (lumens per sq meter) or apx. 10,000 foot-candles. While there isn't any set number for Ideal Light Density, the common consensus is that 4,000 to 10,000 foot-candles provide ample light for thriving Plants. So,

SPACE (L x W) X IDEAL LIGHT DENSITY (4000-10000) = IDEAL TOTAL LUMENS

Ideal Total Lumens represents the total "quantity" of light that all lamps in a space should emit. One thing that is commonly forgotten is that no lamp is perfectly efficient is transmitting it's light, so the actual total lumen output of a lighting system might be significantly less than the rating of the bulb. This is discussed in the optimization section.

Take for example a 3 ft by 3 ft canopy (9 sq. ft total) and between 4000 and 10000 foot-candles means that the space requires between 36,000 and 90,000 lumens. Consider a target of 90,000 lumens (aiming high to counteract the fact that you'll definitely lose some percentage to system inefficiency), used in conjunction with standard output figures for various kinds of lights to compute some rough figures on light quantities:
- 45 X 2 ft. T5 Fluorescents
- 18 X 4 ft T5 Fluorescents
- 1 X 600W High-Output/1000W HID

There aren't enough standard numbers regarding LEDs/Exotics to provide a decent estimation, but if you're using these sorts of lighting sources you should definitely be able to do these calculations yourself.

Light Uniformity
Simply putting 10,000 foot-candles in a space doesn't mean that it is properly lit. If light isn't evenly distributed across the Plant canopy, there will be dead spots where there is less light than there should be, as well as hot spots where too much light causes heat stress on the Plant. The only conventional solution to hot spots is raising the lamp, which decreases the overall intensity and makes the dead spots even worse. So, if you want to make the most out of your lights, uniformity is crucially important. Most uniformity issues arise when using HIDs, because they produce such intense light from a small point of origin. Consider, as a rule of thumb, that a 400W HID should be between 1 and 2 ft above the Plant canopy, a 600W between 1.5 and 2.5 ft, and a 1000w between 2 and 3 ft up off the top of the Plants (emphasis on the phrase "rule of thumb"). This means that the bottom of the lamp must be at the aforementioned height, and the entire fixture/reflector/hanging setup still has to have room above/around the bulb itself. Many people mismatch a low ceiling-height tent with a large HID bulb/tall reflector and end up burning the daylights out of their Plants - just a warning.

For Fluoros, LEDS, and exotics gas lamps, uniformity depends mostly on light placement and the inherent quality of the light fixture. For HIDs, uniformity is also impacted by reflector choice. More on that next, in "optimization" Fluorescent bulbs nested tightly in a fixture bounce light directly into each other, and it loses intensity as it passes through layer after layer of glass. Better efficiency can potentially be achieved by spreading bulbs apart, hanging them individually (vertically or horizontally), or using a contoured reflector housing.

OPTIMIZATION- making the most of your Lights
Why is it important to make the most out of a light? After all, you could argue that instead of spending time and money on efficiency, you could just buy more (or bigger) lights. The biggest reason to focus on efficiency instead of upsizing lights is to keep long-term costs at a minimum. Electricity is the primarily recurring long-term cost of growing Plants indoors and therefore minimizing electrical consumption is a sensible concern for the prudent grower. The two most significant contributors to electricity costs in almost every growing environment are lights and cooling equipment, and both of these factors depend almost entirely on the overall size/number of lights. As a side note and counterpoint, these factors (lighting and cooling costs) matter slightly less in large spaces and/or cooler climates where A/C costs can be significantly lower. Regardless, conserving light and spreading it evenly means running lights as low and cool as possible while keeping overall electricity costs at a minimum. How do we accomplish this?

Reflective Material
Whether tent or room, the material of all surrounding walls and surfaces should be considered for reflectivity. Bright white and reflective aluminum surfaces are both appropriate; the former is a "diffuse reflective" surface and the latter is a "specular reflective" surface, but that doesn't particularly matter. If possible, any space not totally blocked by canopy should be covered with reflective material. Various mylar films are widely available to accomplish this purpose.

Reflectors
NOTE: This all applies mostly to HIDs. It is worth stating because the vast majority of people choose and will continue to choose HIDs. Why?
- HIDs are and have been used in a wide variety of industrial and commercial settings for 50+ years. For that reason, they have been extensively developed in terms of functionality and efficiency. The ability to replace bulbs instead of entire fixtures (not available in most solid-state [LED] or exotic gas lamps) allows variability as well as the option to take advantage of continuing advancements in bulb tech without having to purchase entirely new setups.
- HIDs use excited plasma/gas to create a spectrum of light. So does the Sun. This inherent likeness in the fundamental way that the light is created make HIDs feasible in replacing/surrogating the Sun's radiation.

With that said, one of the major downsides to HIDs is that they emit light directionally in relation to their gas tube, which typically means that the light projects mostly out from the long surface of the bulb in all directions. This is ideal if your canopy encloses the bulb circularly (see Structural Optimization) but for the rest of us, this means redirecting the 50-70% of the light the leaves the bulb in the wrong direction. How do we do this? Reflectors.

There are a wide variety of reflectors on the market. The biggest distinctions are open vs. closed, and ambient vs. cooled. The quality and design of the internal reflective surface has primary impact on both light output and uniformity. Like with reflective surfaces in general, bright white and aluminum surfaces can both be effective. When sized properly, reflectors should be matched to both the bulb and space in consideration. Cooled reflectors allow for large lights to be run on independent ventilation systems (see Loops) to keep cooling costs down. The major downside to cooled reflectors is that they typically require glass, and light loses, at absolute minimum, 10-14% of its intensity passing through glass. Look for reflectors that spread light evenly and efficiently over an area that is close to your canopy size.

Structural Optimization
Structural Optimization is the idea of using strategic plant placement, physical structure, and/or some degree of Plant training to influence the contour of the plant canopy. The "Sea of Green" technique is an example of this wherein many small, tightly packed, and uniform plants allow for an even and dense canopy. "Screen of Green" achieves a similar goal, but through Plant training and trellising instead of placement and cloning. Both of these techniques are associated with a high level of control over canopy height and uniformity, but they also still create a basically flat canopy surface under the light.

A more advanced form of structural optimization involves creating a canopy that surrounds a bare HID bulb, therefore eliminating the need for a reflector and increasing the efficiency of the light. This technique is commonly referred to as "vertical gardening". Because virtually all light is utilized and none is lost to reflector inefficiency, wattage goes a long way with a vertical garden; however, building the necessary infrastructure and successfully training Plants to evenly fill the cylindrical and inward facing canopy can be complicated.

LOOPS
The vast majority of growers will likely end up at least base-lining with HIDs over a relatively flat canopy—mostly for reasons of simplicity. This necessitates reflectors, and for the purpose of efficient climate control, cooled reflectors. Efficiently cooling a light involves a ventilation system of sorts, which is something else that I haven't seen properly explained. There are two distinct strategies for ventilation: Open-Loop and Closed-Loop.

Closed-Loop
In a closed-loop system, the air that passes over the reflector enters from outside of the (theoretically) sealed growing chamber, cools the bulb, and exits without ever touching the growing environment. Why is this useful? First of all for smelly Plants, the ventilated air in a closed-loop system will be scent-free. Also, closed loop systems allow for the use of Carbon Dioxide atmosphere enrichment because the internal atmosphere doesn't cycle out of the chamber. Smelly plants will probably still need some sort of independent air scrubbing system to prevent scent-seep, as well as an air-conditioning system to cool the chamber. Just because the closed loop potentially keeps the Lamp cooled, the light it produces still heats up the room significantly, so A/C is still necessary to balance any reasonably sized lighting system.

Open-Loop
Open-loop systems are commonly used in smaller environments, where a stand-alone air conditioner isn't a viable or efficient means of cooling. In an open-loop system, air is pulled from inside the environment through the light and out of the room, cooling the light and also drawing in outside air to cool the room. The inherent advantage of this system is that it piggybacks on a presumably large and efficient built-in air conditioning system to keep costs down in a relatively small environment. The use of a pre-filter when drawing in the ambient air is necessary to prevent all sorts of contamination/pests. The air that is pulled out will need to be scrubbed on either the input or output end to deal with smelly Plants.

Side note: Closed- and open-loop systems are usually talked about in relation to cooled reflectors, but environments are either closed or open regardless of their use of cooled reflectors.

CONCLUSIONS
Combination & Alternatives
Using multiple, smaller lights as opposed to one big one has a few advantages. First of all, redundancy means that an outage doesn't totally disrupt Plant growth. More importantly, the case of multiple different lights allows for a diversity of spectrum that Plants particularly like. To specify, it has been found that running a HPS in conjunction with a MH lamp creates a spectrum that is advantageous for vigorous Plant growth. Using various kinds of fluorescents and/or LEDs in combination with HIDs has also been shown to have positive results. More, smaller lights results in better spread, more options in terms of placement, and potentially lower running height.

There are a number of neat alternative/supplementary lighting methods but they are mostly way to cool to divulge publicly on the Internet. To get you thinking on the right track, things like skylights and solar tubes allow good old-fashioned natural sunlight to supplement artificial lighting sources. This can have dramatically positive results in terms of Plant growth and vibrancy as long as they glass they are made of doesn't over-filter the light. However, it must be considered that these light portals must be completely dark during the Plant's night time to prevent disruption of the photoperiodic cycle, regardless of what the Sun is doing outside.

Conclusion
One thing you will notice is that I don't cover the specifics of light timing or wiring. This is because the former is incredibly simple, and the latter is case-specific and complex. If you are overloading your circuits, I highly advise you to have a professional electrician check over your setup for safety reasons. Homeowners insurance will do everything in their legal power to deny you any compensation for an electrical fire caused by your own misuse of a household power supply. Just a warning. Anyhow, I hope you have found this to be informative and helpful. Enjoy yourself, do your thing, and stay breezy. No seriously, fans are important.


Signing off,
greeen giant