Is 24 hours of light continuously 24/7 bad for my plants??

[headshake]

that's funny becuase i've read that cannabis plants that grow under 24/0 grow anywhere from 25-33% faster. yet everyone that i have "talked" to says that that doesn't seem so accuate.

from wikipedia:

"Plants usually convert light into chemical energy with a photosynthetic efficiency of 3-6%. Actual plant's photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of CO2 in atmosphere, and can vary from 0.1% to 8%. By comparison, solar panels convert light into electric energy at a photosynthetic efficiency of approximately 6-20% for mass produced panels, and up to 41% in a research laboratory."

so it appears that there is a lot more that goes into it than just how much light is available. if your enviromental factors, assuming we have the same light, only allow you to hit a 3% efficiency than you can hit your plants with 24/0 and it wouldn't be as good as if you had better environmental factors and ran your lights 18/6.

you can't put shit in and get gold out.

also from wikipedia:

"The light-independent reactions are sometimes referred to as the dark reactions, though that term may be misleading as they do not actually require darkness to proceed. The term "light-independent" is used to emphasize that the reactions occur regardless of the amount of light present as long as the proper substrate compounds are available. Even this term can be criticized, however, as the availability of substrates in plants depends on photosynthesis, so the reactions cannot be said to be entirely "light-independent.""

so what that says is your plants don't REQUIRE a dark period. although this term is sligthly skiewed as it implies.

i'm not taking either side, because there is obviously more that goes into getting amazing plants than just hours of light that they receive.

there is a lot we don't know about cannabis plants, that will contiue to unfold as support for this wonderful herb continues to grow.

i love the passion though! you guys both rock!


-shake

[oldmac]

No plants outside in nature have lighting 24 hrs a day. That right there should tell you something! Sorry!

Dear Italiano715,

IMHO I think you are wrong about this. In Alaska you will find that the sun raises during the summer and then just goes round and round; and depending on how far north you are 24 hr sunlight lasts a few days to a few weeks, before the sun sets again. If you would like to see what it does to some C3 plants, just google "Alaska giant vegtables". (it also has a profound effects on humans)
That right there should tell you something. Sorry.

I accept your apology.

[oldmac]

Hey filo6942,

Thank you for speaking up on this subject. I was starting to think I was stuck in a black hole of ignorance.

Again, this is a topic that should not have to be argued about. You can find the answer in a book! I reccomended one that is great to have around, virtually every glasshouse operator I know has this book on his shelf.
"Horticulture, Principals and Practice" by George Arquaah

....or so easy to prove with a simple experiment.

I am not advocating any perticular light schedule to anyone, I happen to use BOTH at the present time! It is what works best for you, in your particular situation. BUT don't tell me or others that it is detrimental to the plant unless YOU CAN OFFER PROOF.

[oldmac]

Hey there jvle,

I'm am trully sorry about "hijacking " your thread. I realized last night that this was going nowhere fast and that even tho we where on topic, I knew it was not right to hold a school yard bitchin' party on your thread.

Sorry again.

BTW on you autoflower project, when you transplant from the cups to a pot, go for one big enough so you don't to transplant again. Their life is so quick, you don't want them slowing at all for anything.

[oldmac]

Hey Shake,

Thank's for the wiki answer. I believe when we deal with a plants cycle, "light-independent" reactions simple means "you don't need light to have it happen" and you are right that it could happen even with light present.

But keep in mind, while the science is in on "vegative" or in horticultural terms "immature" stage, the science is still not clear about the "flowering", or "mature prepoductive" stage. There is still a lot to learn from our beloved plant.
There has been some research that seem to suggest some flower brix conversions only take place in darkness. ( this may be the idea behind some peoples suggestion to put the plants in darkness 1 or more days before harvest.)

[headshake]

thanks oldmac! and i'm sorry for the wiki answers. i don't have near enough knowledge to speak first-hand, either way. the debate just sparked my perpetual curiousty (especially on this subject!) so i did a limited amount of research and felt that what was found contributed positively on the subject.

i am aware the sometimes my eagerness to chime in is not the best thing. i just can't help it!

so the way i look at it is, that because of the difference of opinion i was intrigued to go do some research on my own and learned a bunch (and peaked my curiosty and drive to find more information further)! so either way, regardless of point of view, fact or opinion, i learned somthing, and ya'll are pretty much directly responsible. so ya'll taught, i learned. isn't that the reason that we are all here?!

keep on posting and i'll keep on reading (you too rusty!)!


-shake

[Italiano715]

Originally posted by Xelatoth

I am a biology major currently taking a plant physiology course and I can tell you, at least according to my botanist professor, that plants will not benefit from the extra 6 hours of light in any meaningful way.

Their stomatic gas exchange occurs during the dark period and while they may induce this behavior during constant light anyhow, there is something they can NOT do in 24 hour light:

Their "dark" reactions!!!

A plant has 2 photosystems and both light and dark reactions!

The plant's electron transport chains will be active during light periods to "harvest" the light into chemical energy...

Now, this energy will be stored for use at night!

At night, the plant uses that stored energy for input into the Calivin Cycle!

The Calvin Cycle is the MOST IMPORTANT metabolic pathway in a plant and it finally can convert the chemical energy into useable sugars with the waste byproduct being O2.

Basically, 18/6 is really the only choice

*** 24/0 will allow for a forced Calvin Cycle, but the plant will need to expend MORE ATP and NAD+ to get the same singular glucose molecule... more work for same result = less vigor!

Fo' real.. let us put this to rest as Mother Nature is the best scientist there is!

Peace

This was posted by AlabamaJack in the Hot Pepper Forum. It was from a research experiment.

OPTIMAL PHOTOPERIODS
For tomato, best growth and yield were obtained under a photoperiod of 14 hours (Vézina et al., 1991; Demers et al., 1998b). Photoperiods longer than 14 h did not further increase yield. Photoperiods of 20 and 24 h can even decrease yield and caused leaf chlorosis (after 6 to 8 weeks) (Vézina et al., 1991; Demers et al., 1998b). Although long term use of a 17-h photoperiod does not increase growth and yield compared to 14 h, it might be interesting to extend the photoperiod to 17 h in order to increase total light provided to plants especially during the months with the lowest natural light levels (December-January). However, if a 17-h photoperiod is used, it is important that the dark period be uninterrupted, since splitting the dark period of 7 h in two short nights of 3.5 h (separated by a light period of 4 h) caused leaf chlorosis and decreased growth and yield (Vézina et al., 1991).

For sweet pepper, a 20 h-photoperiod was optimal for plant growth and productivity (Demers et al., 1998a). Yield under continuous light (24-h photoperiod) was equivalent to yield under photoperiods of 15 or 16 h (Costes et al., 1970; Demers et al., 1998a). Extension of the photoperiod from 15 or 16 h to 24 h decreased the average size of pepper fruits (Costes et al., 1970; Demers et al., 1998a).

Continuous light caused some leaf deformities (wrinkles) but no chlorosis in sweet pepper grown in greenhouses. Although long term use of continuous light is detrimental to tomato and pepper plants, tomato and sweet pepper plants can take advantage of the extra light energy provided by continuous lighting for a short period of time. Early vegetative growth and fruit production of tomato and pepper plants were generally improved under continuous light compared the 14-h photoperiod (Demers et al., 1998a, 1998b). However, after that initial period, plants under continuous light grew more slowly than plants exposed to 14-h photoperiod; so that tomato and pepper plant growth and yield under 14-h photoperiod were then equal to or higher than under continuous light at the end of the experiment.

Costes et al. (1970) also observed that continuous light improved the early performance (hastening of flowering and fruit set, increased early yield) of sweet pepper plants compared to a 15-h photoperiod. Therefore, it might be possible to use continuous light for a short period of time (5 to 7 weeks) to improve growth of tomato and sweet pepper, especially during the months with the lowest natural light levels (December and January). However, such a practice should be investigated in order to determine if short term use of continuous light might have residual negative effects on tomato and sweet pepper plants.

NEGATIVE EFFECTS OF LONG PHOTOPERIODS AND THE FACTORS INVOLVED IN THEIR DEVELOPMENT
Tomato and sweet pepper plants do not take advantage (no increase in yield) when grown under photoperiods longer than 14 h (tomato) or 20 h (pepper). Tomato plants, but not sweet pepper, develop leaf chlorosis under continuous light. In the next sections, we will examine the role of the carbon metabolism, pigments, light spectral quality and day/night temperature differential in the development of these negative effects of long photoperiods.

Carbon Metabolism
High starch and soluble sugar accumulations were observed in leaves of tomato plants grown under long photoperiods, and it was suggested that these accumulations could be related to the development of the leaf chlorosis (Bradley et al., 1985; Logendra et al., 1990; Dorais, 1992).

Studies on other species support the hypothesis of a relationship between leaf chlorosis development and starch and sugar accumulations. For example, continuous light caused increased leaf starch and hexose accumulations and leaf chlorosis of eggplants (Solanum melongena L.) (Murage et al., 1996). However, eggplants growing under continuous light but in a CO2-free atmosphere for 12 h per day accumulated less starch and hexoses, and did not develop leaf chlorosis.

Exposure of tomato and sweet pepper plants to continuous light resulted in increased foliar contents in starch in tomato and sweet pepper, in hexoses (glucose and fructose) in tomato and sucrose in sweet pepper (Dorais et al., 1996; Demers et al., 1998a, 1998b). However, the reduction of the number of fruits on the plants did not modify the pattern of accumulation of starch and sugars in leaves of tomato and sweet pepper plants exposed to photoperiods of 14 and 24 h (Demers et al., 1998a, 1998b). Moreover, the reduction of the number of fruits on the plants did not influence the severity nor the date of appearance of the foliar chlorosis in tomato plants grown under continuous light. This indicates that accumulations of starch and soluble sugars are not caused by a limiting sink capacity. If there is a relationship between the excessive starch and soluble sugar accumulations and the development of the negative effects (leaf chlorosis, decreased growth and productivity) of the long photoperiods on tomato and sweet pepper, it is most likely a limitation of the carbon metabolism at the leaf level which is responsible for these accumulations.

In tomato, the use of continuous light caused, in addition to the foliar chlorosis and increased foliar contents in starch and hexoses, a reduction of the photosynthesis rate and of the activity of the sucrose phosphate synthase (SPS) enzyme (Demers, 1998). These reductions in photosynthesis and of SPS activity occurred between 6th and 8th week
under continuous light, i.e. about at the same time as the foliar chlorosis appeared, while starch and hexoses contents in leaves increased during the first 4 weeks of the experiment.

Since the reduction of the SPS activity occurred after the increase in starch and hexoses, it is thus impossible that the reduction of the SPS activity is responsible for these accumulations. However, it is possible that the SPS activity in vivo is limiting, which would explain the hexose increase. This suggests the limiting step of the export of photosynthates is the synthesis of sucrose in tomato and would explain the absence of growth and the productivity increase under continuous light. Furthermore, the increased hexose levels in the cytoplasm, by a feedback effect, would limit the export of the triosephosphate (photosynthesis products) out of the chloroplast, which would then be redirected towards starch synthesis, thus explaining the increased starch contents.

Moreover, the increased accumulation of starch would generate, by a feedback effect, an overload of the Calvin cycle, which would gradually cause the observed decrease of the CO2 fixation rate. Are the starch accumulations responsible for the leaf chlorosis in tomato? It is possible that the overload imposed on the Calvin cycle (decreased photosynthesis) could limit the use of the reducing potential (ATP, NADPH) produced by the luminous phase of photosynthesis, thus causing an overload on the electron transport chain and the photo-oxidation of the chlorophylls (decrease in the leaf chlorophyll contents), and thus explaining the observed leaf foliar chlorosis. Transgenic tomato plants (in which a gene coding for the SPS enzyme was incorporated and overexpress this enzyme) could be used in future studies to test if accumulations of starch in leaves are responsible for the development of chlorosis observed in tomato plants exposed to continuous light. Transgenic tomato plants (overexpressing SPS) have higher photosynthesis rates and accumulate less starch and more sucrose than non-transformed
plants, especially under conditions of saturating light and CO2 (Galtier et al., 1993, 1995; Micallef et al., 1995). One can put forth the assumption that, under continuous light, leaf starch contents would be lower in transgenic plants than in normal plants. If this is the case, the reduction of the leaf starch content in transgenic plants should thus prevent the development of the leaf chlorosis, or at least decrease its severity.

In sweet pepper, the use of continuous light caused an increase in the leaf starch and sucrose contents, but did not affect leaf hexose contents, photosynthesis rates and SPS activity (Demers, 1998). The increased foliar contents in sucrose indicate that SPS activity in sweet pepper is not limiting as in tomato. Increased accumulation of starch in
sweet pepper plants exposed to continuous light would be explained by the fact that continuous light results in a longer period of time over which starch synthesis occur, but without overloading the starch synthesis pathway. Thus, starch accumulation in sweet pepper under continuous light would not be important enough to cause a reduction in CO2 fixation (no overload of the Calvin cycle). Increased leaf contents in sucrose suggest that sucrose export would be possibly limiting. In sweet pepper plants, the export rate of carbon (as sucrose) out of the leaf is constant, and the export rate would be limited at the level of the loading of sucrose in the phloem (Grange, 1985, 1987). This would explain why the growth and the productivity of the sweet pepper plants do not increase under continuous light.

Pigments
In growth chambers, continuous light caused leaf chlorosis, decreased photosynthesis rates, and reductions in leaf contents in pigments (chlorophyll a and b,
carotene, xanthophylls) in both tomato and sweet pepper plants (Demers, 1998). Leaf chlorosis, decreased photosynthesis rates and loss of pigments were more important and occurred earlier in tomato plants than in sweet pepper. Compared to sweet pepper plants, EPS ratio (epoxidation state of the pigments of the xanthophyll cycle) was lower in tomato, indicating a greater need for energy dissipation and a more important state of stress (caused by excessive light). Pigments such as carotene and xanthophylls (violaxanthin, antheraxanthin, zeaxanthin) play a significant role in the protection of the photosynthetic apparatus against damage that could be caused by an excess of light.

Carotene and xanthophyll levels were higher in sweet pepper plants than in tomato. Thus, sweet pepper has a better protection against the degradation of chlorophylls, which would explain why leaf chlorosis appeared later and were less severe in sweet pepper.

---- end copy/paste ------------
Leaving lights on 24/7 is OK and perhaps beneficial (not counting the cost of electricity) for no more than seven and maybe as few as five weeks and after that it is detrimental.

Mike

I know ^^^ isn't cannabis....well you get the point....healthier plants with a dark period.

1st quote link: 18/6 vs 24/0
2nd quote link: What are the Consequences of Leaving Lights on 24/7

[Italiano715]

Photosynthesis

Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae (Kingdom Protista). Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.

[Leaf Cross-Section] Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins), and the stomates. The upper and lower epidermal cells do not have chloroplasts, thus photosynthesis does not occur there. They serve primarily as protection for the rest of the leaf. The stomates are holes which occur primarily in the lower epidermis and are for air exchange: they let CO2 in and O2 out. The vascular bundles or veins in a leaf are part of the plant's transportation system, moving water and nutrients around the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs.

As you hopefully recall, the parts of a chloroplast include the outer and inner membranes, intermembrane space, stroma, and thylakoids stacked in grana. The chlorophyll is built into the membranes of the thylakoids.

Chlorophyll looks green because it absorbs red and blue light, making these colors unavailable to be seen by our eyes. It is the green light which is NOT absorbed that finally reaches our eyes, making chlorophyll appear green. However, it is the energy from the red and blue light that are absorbed that is, thereby, able to be used to do photosynthesis. The green light we can see is not/cannot be absorbed by the plant, and thus cannot be used to do photosynthesis.

The overall chemical reaction involved in photosynthesis is: 6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2. This is the source of the O2 we breathe, and thus, a significant factor in the concerns about deforestation.


There are two parts to photosynthesis:

The light reaction happens in the thylakoid membrane and converts light energy to chemical energy. This chemical reaction must, therefore, take place in the light. Chlorophyll and several other pigments such as beta-carotene are organized in clusters in the thylakoid membrane and are involved in the light reaction. Each of these differently-colored pigments can absorb a slightly different color of light and pass its energy to the central chlorphyll molecule to do photosynthesis. The central part of the chemical structure of a chlorophyll molecule is a porphyrin ring, which consists of several fused rings of carbon and nitrogen with a magnesium ion in the center.

The energy harvested via the light reaction is stored by forming a chemical called ATP (adenosine triphosphate), a compound used by cells for energy storage. This chemical is made of the nucleotide adenine bonded to a ribose sugar, and that is bonded to three phosphate groups. This molecule is very similar to the building blocks for our DNA.

Structure of ATP

The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn't directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Actually, notice that the first product of photosynthesis is a three-carbon compound called glyceraldehyde 3-phosphate. Almost immediately, two of these join to form a glucose molecule.

Most plants put CO2 directly into the Calvin cycle. Thus the first stable organic compound formed is the glyceraldehyde 3-phosphate. Since that molecule contains three carbon atoms, these plants are called C3 plants. For all plants, hot summer weather increases the amount of water that evaporates from the plant. Plants lessen the amount of water that evaporates by keeping their stomates closed during hot, dry weather. Unfortunately, this means that once the CO2 in their leaves reaches a low level, they must stop doing photosynthesis. Even if there is a tiny bit of CO2 left, the enzymes used to grab it and put it into the Calvin cycle just don't have enough CO2 to use. Typically the grass in our yards just turns brown and goes dormant. Some plants like crabgrass, corn, and sugar cane have a special modification to conserve water. These plants capture CO2 in a different way: they do an extra step first, before doing the Calvin cycle. These plants have a special enzyme that can work better, even at very low CO2 levels, to grab CO2 and turn it first into oxaloacetate, which contains four carbons. Thus, these plants are called C4 plants. The CO2 is then released from the oxaloacetate and put into the Calvin cycle. This is why crabgrass can stay green and keep growing when all the rest of your grass is dried up and brown.

There is yet another strategy to cope with very hot, dry, desert weather and conserve water. Some plants (for example, cacti and pineapple) that live in extremely hot, dry areas like deserts, can only safely open their stomates at night when the weather is cool. Thus, there is no chance for them to get the CO2 needed for the dark reaction during the daytime. At night when they can open their stomates and take in CO2, these plants incorporate the CO2 into various organic compounds to store it. In the daytime, when the light reaction is occurring and ATP is available (but the stomates must remain closed), they take the CO2 from these organic compounds and put it into the Calvin cycle. These plants are called CAM plants, which stands for crassulacean acid metabolism after the plant family, Crassulaceae (which includes the garden plant Sedum) where this process was first discovered.

Photosynthesis

[Rusty Trichome]

^^^ Nice find.

Love the Wiki response...at least someone out there is trying...

In response to the 24hrs of light a day in Alaska...are you sure it's 24 hours of direct light? You sure it has all to do with the light, and not the temps...? What about UV and visible light refelcted off the moon? No correlation there...? There are signs from both sides of the aisle of the possibility of influence with and without dark or rest periods.

How Does Darkness Affect Plant Growth? | eHow.com

Cabbages grow big in Alaska when sunlight is abundant. The photosynthetic process occurs most readily when the sunlight available to the plant is the greatest. This is why plants in the tropics grow so large. They are near the equator where the sunlight is directly overhead much of the year. However, photosynthesis can occur in the dark. It does not occur as rapidly as during the daylight, but it is possible. If this were not the case, plants would shut down entirely every night when the sun went down.

Therefore, the periodic darkness of nighttime does not affect plant growth very much. In areas of the world, like Alaska, that experience seasonal increases in the length of daylight photosynthesis does make plants grow very large. Although Alaskan vegetable gardens are filled with plants that do well with cool temperatures and a short growing season (turnips and cabbage, for example), they tend to grow very large. This is because the sunlight hitting the gardens can do so for up to 20 hours a day.

Ecology Of The Night

Plants do not normally react strongly to the simple experience of darkness. However, autotrophic plants depend on light for their food, so darkness (the absence of light) influences their growth, and prolonged darkness is deadly. Certain unicellular algae (both marine and soil) avoid this problem in an interesting way. In light, they photosynthesize normally and make all the carbon compounds they need. But in darkness, they rapidly develop a powerful transport system that pumps external organic carbon compounds (particularly sugars) into their cells, providing an alternative source of energy and metabolites. The transport system is lost and photosynthesis begins when the light is turned on, and the rate of photosynthesis and transport may vary inversely with the light intensity. This mechanism provides a strong competitive advantage for these organisms.
The periodicity and duration of light and darkness is powerfully important in the development of many plants. The measurement by plants of light/dark periodicity enables them to fit their growth patterns to the seasons, and the duration of periodic darkness is critical for the onset of flowering in many higher plants. Thus, relatively strong light pollution during the night (as from street or flood lights) may seriously disturb the normal growth, development, flowering and senescence patterns of sensitive plants.
...
In general, plants are not usually much affected by the absence of absolute darkness at night, that is, by light pollution. Bright illumination at night may affect the flowering of sensitive plants, and other aspects of growth and development behaviour, including maturation and senili-ty, may be affected. But lower levels of light pollution, which might affect animal behaviour or astronomical observation, seldom affect plants in any significant way. Plants cannot be likened to the canaries in coal mines as indicators of excessive levels of pollution.

[oldmac]

[quote=Italiano715]Photosynthesis[/QUOTE

To whom it may concern;

The point that I have made continually here, is this use of 24 hr photoperiod is for a "immature phase plant" or in terms we are all familar VEGATIVE state.
Most of these papers deal withe the entire life cycle of the plant, including "mature phase" we know as Flowering. IMHO a plant needs a dark photoperiod of at least some duration during this time. But not when it is in VEGATIVE state.

This is an excert of the above clip/paste:

>"Costes et al (1970) also obsevered that continuous light improved the early performance (hastening of flowering and fruit set, increased early yield) of sweet pepper plants compared to the 15hr photoperiod. Therfore it might be possible to use continuous light for a short period of time (5-7wks) to imrove growth of tomatoes and sweet pepper, especially during the months of lowest natural light levels (Dec/Jan). However such a practice should be investigated in order to determine if short term use of continuous light has residual effects on tomato and sweet pepperplants."<

At least I have you all looking and reading, next we need to work on our reading comprehension.

There are even more recent studies, and all seem to indicate the same thing, I can only conclude that it is not only NOT harmfull to use 24/0 for vegative growth, it seems to INCREASE growth.

OK Rusty, you did not want to read up on this, but Ital at least did. You did not want to accept any proof I had to offer, what about above? Italian715 is the source of this and he's trying to support your position.

Now with all this said plus all the additional rhetoric, I need to say this to you; I have no problem at all with your using 18/6 (I use it too) or if you want to say you have a feeling that your plants need a rest or that you think they do better that way, fine. I previously mentioned the human tendicy to "humanize" our plants, project our feelings and needs onto them. I realized I do it too, just last night a couple of minutes past 8:00 when my bloom room lights came on, I walked in to check on my girls with "good morning ladies how are you all doing!". Yup, I talk to my plants and somehow I think they like it. No science, no studies, but I really think they do better when I talk to them..... go figure.

This topic and others like it could be great to discuss, if you and I and others here could get less emotional and personnel with our debates and try to hold discussions instead. I'm willing to try and do better in the future.