Artificial lighting (again again)

[AnTTun]

OK, I have to admit that something is wrong with my chicken box. Techie details first:

LxWxH = 80x60x45 cms (32"x24"x18"), all white inside, insulated outside.
5 fluorescent lamps on 'ceiling', 4 cool white (4000K) and 1 'gro lux' (blue and red spectrum), 18W, 60 cms (24")
Temperature inside the box is around 30 C.
Light period is 14 hours.

Young seedlings seem to be doing OK. But older seedlings of columnar kind, pereskiopsis and selenicereus are growing too tall & too thin. They are not pale green, and spines don't seem too weak but I'm pretty sure that for ex. selenicereus that is 25 cms long should be more than 4-5 mm thick, as some cereus that is 3-4 cms tall should be more than 4-5 thick. I water them every one or two weeks, and add fertilizer once a month.

My guess is that they are not getting enough light, or not enough certain kind of light. If I am right (opinions please, please), I would add two more lamps, but what kind of light? Daylight (6000K) ? Warmwhite (3000K)? Both? Another red/blue with...?

[iann]

You light levels should be about right for most species for the first few months. Of course they are nowhere near enough for older plants. I'm not familiar with the types you are having trouble with. I would imagine that another two tubes would be pretty harsh for newborns, but maybe you can partially hide them or shade them.

In the case of "somewhat white" light, adding more blue should produce more compact plants although it is also more stressful for younger seedlings. The first thing you might notice is a sensitive species going red or brown.

Another important factor affecting etiolation is temperature. Plants kept cooler, especially cooler at night, will grow more compact.

[anders]

I have never grown Cereus from seed, but it sounds as if it is too thin. A 25 cm long Selenicereus should be thicker, roughly twice the width of yours. I would not grow a plant that long under artificial light.
Your setup is similar to mine, where I can grow seedlings until they are about 2—3 cm, it depends on the species.

[AnTTun]

As usual, when one searches the Net on some quite common topic, it becomes hard to decide what website should be used as relevant. The more of them I read, the more confused I get. But lets say following info is more or less common to all of them.

How Light Affects Plants

Plants use the energy from light for more than photosynthesis. The effect of light is still one of the most complicated ques¬tions in plant study today. The four aspects of plant growth most affected by light are:
• photosynthesis — converting light, air and water into carbohydrates and oxygen
• chlorophyll synthesis — building the plant cells that perform photosynthesis
• photoperiod — sensitivity to the length of day
• phototropism — movement toward a light source.
..................................
Almost all life on our planet depends on photosynthesis. Plants produce food for themselves and others when they use the energy from light to convert carbon dioxide and water into carbohydrates and oxygen. The substance that performs photosynthesis is called chlorophyll. Studies have shown that chlorophyll absorbs blue (short wavelength) and red (long wavelength) light for photosynthesis. However, chlorophyll doesn't absorb green (medium wavelength) light. It reflects the green light, which is why chlorophyll -and therefore most leaves -look green.
..................................
Plants are referred to as either high-energy or low-energy plants, depending on the intensity of light they need. For low-energy plants (which includes most houseplants), standard GRO-LUX lamps provide the right balance of wave-lengths. However, high-energy plants seem to require more light in the far-red portion of the spectrum, and grow better if half of the lamps are standard GRO-LUX and half are wide-spectrum GRO-LUX.



(Doesnt't really matter if its called Gro-lux, Fluora... blah blah, important is which part of spectrum lamp emits - AnTTun)

High-energy plants also require more light than low-energy plants. An easy way to figure out how much light energy your plants need is to find how many watts of fluorescent light they need per square foot, and use that number to determine the number of lamps you need.

For example, assume that your plants have no sunlight at all, your lamps are 12-15 inches above your plants, and that you are using 4-foot fluores¬cent lamps to light a plant shelf that is 2 feet wide and 4 feet long (8 square feet). Low-energy plants require about 15 lamp watts per square foot, so you would need 120 watts, or three 40-watt fluorescent lamps. High-energy plants require at least 20 lamp watts per square foot, so you would need at least 160 watts, or four 40-watt fluorescent lamps. You can accomplish this by adding more lamps, adding a reflector above the lamps to direct more of the light toward the plants, or moving the lamps closer to the plants. Germinating seeds or cuttings being rooted only require about 10 lamp watts per square foot, but the lamps should be closer — only about 6-8 inches above the soil or tops of the cuttings. If your plants receive some natural sunlight, you can decrease the amount of light from the lamps proportionately. Note that these recommendations for watts per square foot are for fluorescent lamps only. If you are using incandescent lamps, you need four times as many watts per square foot.

And to (try to) sumarize all this.... I'll try to add 2 more lamps that cover blue/red spectrum and watch plants for another month. Growth of older ones and damage of seedlings. Seems there is no other way than to learn hard way

[iann]

Amazing how a seemingly straightforward set of facts can lead to mistakes of urban myth proportions

[anttisepp]

<...>For wintergrowing plants I use ...<...>

<...> Save you lights for things that need the light in winter, winter growers <...>

Very interesting discussion. Torbjorn, iann, what do you mean under the term "wintergrowing plants"? Are there such ones among cacti? Sorry for offtop.

[iann]

I don't remember what I said about winter growing plants but I probably wasn't referring to cacti. Probably the mesembs that are strictly summer dormant and simply won't perform without good winter lighting. Gibbaeums, Mitrophyllums and friends, stuff like that. Conophytums don't really need lights, Lithops certainly don't, and they are really a waste for cacti that will do very little under most winter lights that they won't do in a window or even in a cold greenhouse.

[AnTTun]

After spending 'few more bucks' chicken box looks like this:



I hope adding few lamps that cover blue/red spectrum will turn into good investement in a month or two. Reason(s) for additions looks like this:







I'm affraid I'll have a lot of cutting to do in spring If they continue to grow this thin, so lets keep fingers crossed.

P.S. I had to take reflector out, it's main purpose was to heat the box up when needed. But 7 lamps heat enough. As a matter of fact, I might have to consider adding cooling fan because temp goes to 30-32 C.

[anttisepp]

It seems to me that the results will be better if distance between plant's tops and lamps should be not more than 5 cm. IMHO

[iann]

It seems to me that the results will be better if distance between plant's tops and lamps should be not more than 5 cm. IMHO

Makes (almost) no difference.

Watch out for those pink lamps losing output after a few months. I don't know exactly what your white ones are, but good quality white fluorescent tubes can maintain 90%+ output until failure after maybe 20,000-30,000 hours. The pink ones can lose 20% of output after a thousand hours or so, and then quite a lot more by the time they fail. Also they just plain don't last very long, but probably not too bad when run as a plant light without much switching on and off. Back in the dark ages, the advice used to be to swap out plant light tubes every 6 months.