Growing under lights: 2015
 

I did a lot of poking around on the topic of artificial lighting in the last six months or so. An awful lot has changed in the last 5 years and LEDs are rapidly emerging as the single best solution for most people. I'll summarize what I learned.

Chlorophyll in all plants - aquatic, terrestrial, epiphytic, whatever - absorbs mainly photons with energies near two specific wavelengths. Such light appears bluish and pinkish to us. Other wavelengths are not used at all and it is a waste electricity of to produce them.

Plants grow great under pinkish and bluish light but look weird to us, so most hobbyists are willing to provide light at other wavelengths for aesthetic reasons.

Metal halide (MH) bulbs produce adequate light for plants. They are expensive, extremely hot to run, and use much more electricity than other kinds of growing lights, much of which is wasted producing heat. They will produce third-degree burns in humans in less time than it takes to withdraw your hand. They will explode if a drop of water hits them when lit, showering near-molten glass all over you and your plants. Their light output declines with age. People make the argument metal halide both lights and heats the growing space during winter, but it costs much less to use different light sources plus heaters to accomplish the same thing. Almost nobody starting from scratch would use metal halide lights nowadays.

Incandescent lights can provide adequate light for plants. They are also hot and cost a lot more to operate than fluorescent lights. Few people starting from scratch would use incandescent lights.

Fluorescent lights of all types and sizes (standard, CFL, T5, T8, T12, spiral...) can produce adequate light for plants. CFL stands for Compact Fluorescent Lighting. These use much less electricity than similarly-rated incandescent lights. The T number refers to the diameter of the tube. T12 is the standard size for overhead lighting; these tubes tend to be the least expensive initially. Tube sizes are not interchangeable in fixtures. All white fluorescent lights emit many wavelengths, including those not used by plants, so electricity is being wasted on producing useless wavelengths.

Among other qualities, fluorescent lights are rated by something called color temperature, reported in Kelvin units, K. This is a rough approximation for light wavelength produced by the fixture. Around 6,500K is needed to grow plants. This is often labeled as "daylight" but you must look at the K rating, because different manufacturers use different terminology. Aquarium fixtures are often used by plant growers. 10,000K tubes provide a brilliant white light that is great for viewing fish but poor for growing plants. "Cool White" tubes have a K rating too low for plants. The K rating is often printed on the tube and is always on the package in the US.

All fluorescent tubes diminish in output as they age. The plants will notice this before your eye does. Most people recommend changing fluorescent lights every 9-12 months because of the diminishing light output.

Standard 4 foot long T12 double-tube shop lights with 6,500 K bulbs are adequate for plants. This is a very low-cost solution to install, but when factoring in electricity cost and fixture lifespan, it is no longer the best. Higher wattage tubes are better than lower. The plants will have to be quite close to the tubes. They produce some heat but it would be unusual for a person to be burned by the fixture.

T5 lights are often used for growing plants - aquatic and otherwise. T5 and their fixtures are more expensive initially than T12, but are supposed to wind up using a lot less electricity for the output over time, so they are supposed to wind up costing less. They produce a fair amount of heat, enough to be a problem for some aquarists and non-aquatic plant hobbyists. Fixtures may burn humans.

CFL lights rated 6,500K provide adequate light for plants. They produce less heat than T5 tubes. A 200 Watt equivalent spiral CFL is available that fits into a standard-base clamp-on shop light with a reflector. I have used this solution to bring aquatic plants needing extremely high light intensity through the winter indoors: water hyacinth, hornwort, Azorella. T5 fixtures are supposedly cheaper than CFLs overall but I was not willing to accept the hot fixtures. I can touch the 200 Watt equivalent spiral bulb. It is clearly hot, but there is plenty of time to remove my hand before being burned. The clamp reflector does not heat up enough to burn my hand. These bulbs also need to be close to the plants.

Light-emitting diodes (LEDs) use a different technology from other fixtures. Each LED emits only one wavelength of light. If LEDs/wavelengths are chosen properly, plants can grow under these lights, and electricity will not be wasted on useless wavelengths. By their nature LEDs last an extremely long time with minimal decrease in light output. The lights themselves emit little heat, but they need a transformer to convert household electricity into a voltage they can use. The transformer produces some heat, but generally not enough to burn a human, and it is well away from the plants. LEDs fixtures initially cost a lot more than fluorescent fixtures and tubes, but the electricity savings are supposed to be large enough that the payout period is a year or less. I know a large aquatic nursery owner who switched his entire operation from CFL to LED and the payback period was less than a year.

Commercial vegetable production is being switched to LED lighting because electricity costs are much less over time. Gigantic warehouses are illuminated in pink and blue only. These warehouses are tightly sealed to prevent entry of pests, so insecticides need not be used. Plants are grown hydroponically in nutrient solutions adjusted daily based on analysis of random leaf samples.

White aquarium LEDs seem adequate for some plants, but how to measure intensity of light produced and how to decide which fixtures work well are still not well understood. Aquarium LEDs generally provide neither wavelength nor light intensity information.

We tend not to like the look of only pink and blue LEDs, so fixtures are available containing white as well. People posting to this board sell them. I have not tried any of them but I would expect they work well.

To sum up, if you have minimal money available, you probably shouldn't be growing plants under lights, especially orchids, but that never stopped me when I was dirt poor. If you want to minimize initial outlay, or you don't care about electricity cost now or in the future, use a T12 or CFL system with 6,500K color temperature bulbs in the highest Watt equivalent you can get, and change your bulbs every 9-12 months. Anybody else should use LEDs designed for growing plants.

"Metal halide (MH) bulbs produce adequate light for plants. They are expensive, extremely hot to run, and use much more electricity than other kinds of growing lights, much of which is wasted producing heat. They will produce third-degree burns in humans in less time than it takes to withdraw your hand. They will explode if a drop of water hits them when lit, showering near-molten glass all over you and your plants. Their light output declines with age. People make the argument metal halide both lights and heats the growing space during winter, but it costs much less to use different light sources plus heaters to accomplish the same thing. Almost nobody starting from scratch would use metal halide lights nowadays."

I am certainly no expert, but I disagree with your assessment of MH lighting. Yes, they can explode if water gets on them when hot, but a glass enclosed reflective hood eliminates that problem. Yes, they generate a lot of heat. But for me, it would be impossible to create a temperature difference between day and night without my MH light. An MH light makes it easier to grow orchids of varying sizes than trying to grow them under LEDS or fluorescents. As to cost, I think MH lighting is a relatively efficient way to provide a lot of light for a large area.

I think there are too many variables in orchid growing to categorically rule out one sort of lighting over another. We all know that what works for one person may not work for another. That is what makes growing these plants so challenging and fun.

The main disadvantage of MH lighting is the heat. If the heat is a desired thing, the main disadvantage is removed. Bulb replacement over time adds considerably to the overall cost, but it's spread out over a long period. I have lots of MH stuff laying around and would use it if I had a basement growing space.

Very nice and detailed post, Estación! Here are a couple additional details, which you may be interested in.


It is true that chlorophylls have two absorption peaks (red and blue). However, the last statement is not correct. In the area where photons are absorbed (called photosystems), there are other pigments (such as carotenoids), which can absorb other wavelength. The energy absorbed by other pigeons of photosystems can be passed to the reaction center of the photosystems, and the energy can be converted to chemical energy (ATP and NADPH). So in reality, something called photosynthesis action spectrum is more relevant than absorption spectrum. A lot of people are confused about this.

You probably want to look at the table 3 of this paper. Ceramic MH isn't as efficient as the top rated HPS or LED, but it is fairly efficient (5th column Photon efficiency).
HPS: 1.7-0.95 micromol/J
LED: 1.7-0.89 micromol/J
CMH: 1.46-1.25 micromol/J
Florescent: 0.84 micromol/J

Also, if you look at the 5 year cost (including the intial cost and electricity), from the cheapest to more expensive:
HPS < CMH < LED < florescent
This is the right most column of Table 3.

A lot of people consider only the initial fixture cost, but indeed, the electricity becomes the main cost over a couple years.

In the US, T8 is the standard size (it used to be T12 is the standard, but it is getting more difficult to find, because it is so much less efficient). Some fixutres can take T8 and T12. There are also 2 kinds of T5 (normal output and high output), where you have to much the bulbs with the fixture (ballast).

With efficiency, T5 NO is the most efficient, then T8 and T5HO, then T12. T5NO and T5HO is more efficient in the hot operating condition. So in lower temp, T8 could be more efficient than T5HO.

I'm not sure what you mean by "well understood". There is nothing tricky about LED measurement. The best is using spectrophotometer, but it is not something most of us can afford. Quantum PAR meter gives a pretty good quantification of light relevant for plants. With white light, even the lux/footcandle meters can give the idea of how much your plants are getting.

There is no advantage of going T12 over T8, so T8 is a better choice. Also, people shouldn't get too hyped up about LEDs, though. There are humongous variation in the efficiency among fixtures (as the Table 3 of the paper showed). Most cheap ones are slightly better than florescent light (in efficiency). To get high efficiency LED, you either need to pay quite a bit at first or you need to go to DIY route (which is my favorite).

Lots of light!
 

I have just purchased a T5 HI- output light fixture with 2-24 watt tubes of blue light, 6500k. Wow! Very, very bright light!! Now I wonder if this type of light is not TOO much for orchids. I'm keepiing the fixture about 4 feet from the plants, and watching closely to see what effect it has. This is day one.
I purchased a half dozen "rescue"plants from the local farm store where they had almost killed them with overwatering. No tags, nothing to know what they are xcept they are orchids of some kind. Also trying to revive two cattley
as that I overwatered and repotted after joining orchidboard and learning enough to be dangerous. I will update as I learn more about this lighting thing.

T5 HO part is myth part is true.
T5 HO lamps can be really good for plant growth, provided it is of good quality.
The cheap ones are good only for domestic lighting (you think plants are doing well). The expensive, specially manufactured for horticulture are good, but if you do a count (compared to other light emission) reach the conclusion that you must meditate.
The K is how plants look to you.
The PAR is roughly how much energy the plants get.

:waving
The flour tubes I got with the T5 are HO, horticulture.
The store is here in Humboldt Cnty, Ca. And is where the Marijuana growers buy their supplies! Been reading about lights today on Orchidboard and decided maybe I don't have ENOUGH! But yes, it'll be fine. I can always suppliment with daylight. Bright sun today, temp is a HI 72. Normal here is 55 night, 65 day. Perfect for outdoor grows, so I understand. Thanks for the feedback!
Later that same day: purchased a two-tier grow bench with T5HO flour tubes @ 24 watts, two per shelf. Not actually a bench, they call it a "cart", but has no wheels.
40x24x12". Won't get here till middle of August; reckon they have to build it; outrageous price of $229! Well, that's inflation for ya. I can do wheels.

:rofl: good joke

The plants aren't getting much light if you place it at 4 feet. Try 2 feet or so for the relatively low light orchids. Cattleya can be around 1 foot (from the bulbs to the leaves).

Ah yes grasshopper! I understand. That's why I got the cart. She-who-must-be-obeyed thinks she would like orchids "here", I think maybe "there". The "cart" can be moved, and has plenty of room to hang lights. Can't really
"Hang" lights yet;but yes, I hear the "closer". When I turned on the lights they were SO much brighter than the "old" style I was afraid they'd be too much, but after reading here today I can see I was way wrong. Thanks for the feedback.

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What? (:scratchhead:)