Extending Photosynthesis Activity by Artificial Light

Various plants, usually part of the food chain, are grown over extended hours in places like Iceland using artificial light and supplemental warmth provided by geothermal energy there. It seems to work.

Typically, extending day length with artificial light will only benefit vegetative growth. If you want to hasten fruiting/ripening, you would be better off introducing artificial darkness, and shortening the day length.

It is feasible to extend the day length and not revert to vegetative growth even for plants with photo-dependent flowering.

Plants with photo-dependent flowering require a certain amount of uninterrupted darkness to remain in the flowering stage. In most plants, it takes about 2 hours after the lights go out, or more precisely after light in the 600 to 700 nm range is eliminated, for phytochrome of the type Pr to build to sufficient levels, and then the remaining time to induce flowering.

The interesting thing is light in the 600-700 nm range converts phytochrome type Pr to phytochrome type Pfr. Similarly light in the 700-760 nm range converts Pfr into Pr.

Daylight could feasibly be extended up to two hours by: filtering light in the 600-700nm range for the last two hours; providing a strong source of ~730 nm light at the end of the light cycle; or a combination of both approaches.

I am uncertain if this will lead just to a reduced time to maturity or just an increased yield.

Another way I find interesting to modify growth and flowering is the use of gibberellic acid.

Oh you can do much better than that.....Welcome to the wonderful world of hydroponic gardening...

http://www.designbuzz.com/entry/hydroponic-garden-requires-no-soil-and-fertilizers/

You can speed up plant growth by an increase of the hours of light. Whether you will get growth to mature in that time frame is dependent on the crop. Also some plants need other environment conditions to happen to bear fruit. Some of those need a drop in the hours of day light.

What are the plants which need a certain period of darkness?. Once we illuminated a footpath going through a rice-field in the night for our staff to go to our factory from their residences. After some time the rice-farmers said to switch it off (and not to switch on for more than a little period) to enable the rice-plant to flower.Why???

Shorter periods of daylight and longer periods of darkness are the trigger mechanism for most plants to stop vegetative growth, and switch into reproductive mode. Most, if not all, of the fruits and vegetables we eat are nothing more than seed pods.

Shorter days signal the advent of winter..................time to fruit and make seeds.

For UV light to really supplement the plants it has to be close to them. My farmer friends start their seedlings under UV before spring, and give them 16 hours of light per day. For leafy greens grown indoors, some people recommend leaving the lights on 24 hours a day. Longer days help to compensate for the lower light levels provided by the fluorescent tubes, which are placed near the tops of the plants and raised up as they grow.

For vegetative growth, high colour temperatures are recommended (5000 K or higher), although some people also use the cheaper 'cool white' bulbs (4100 K) as an all purpose grow light. To promote flowering and fruiting, low colour temperature bulbs are recommended, and as kramarat pointed out, a period of darkness is also required by most plants to flower and fruit (tomatoes, for example, must have a night time).

Two to three hours of extra light by UV per day doesn't sound like much to me, if you hope to get significant results. I doubt it would cut the ripening time of fruit by a full two weeks. The results would also vary depending on what crop you are thinking of. Tomatoes for example, always seem to take the full time to ripen, even with 14 to 16 hours of sunlight as we get in summer here. The best way to get earlier tomato fruit is to choose an early setting variety.

"Ripening agents speed up the ripening process.

They allow many fruits to be picked prior to full ripening, which is useful, since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being gassed with ethylene. A similar method used in parts of Asia is to put a plastic cover over a bed of slightly green-harvested mangos and a few small open containers of clumps of calcium carbide. The moisture in the air reacts with the calcium carbide to release the gas acetylene (ethyne), which has the same effect as ethylene. Ethylene is not emitted by the plant naturally, and cannot activate the ripening of nearby fruits, rather, it is used as a hormone within the plant.

Calcium carbide is used for ripening fruit artificially in some countries. Since industrial-grade calcium carbide may contain traces of arsenic and phosphorus, the use of this chemical for this purpose is illegal in most countries. Calcium carbide, once dissolved in water, produces acetylene, which acts as an artificial ripening agent.Acetylene is believed to affect the nervous system by reducing the oxygen supply to the brain. Agricultural industry PR claims that acetylene is not sufficiently reactive to affect consumers.

Catalytic generators are used to produce ethylene gas simply and safely. Ethylene sensors can be used to precisely control the amount of gas.

Covered fruit ripening bowls are commercially available. The manufacturers claim the bowls increase the amount of ethylene and carbon dioxide gases around the fruit, which promotes ripening.

Climacteric fruits are able to continue ripening after being picked, a process accelerated by ethylene gas. Non-climacteric fruits can ripen only on the plant and thus have a short shelf life if harvested when they are ripe."

GROWTH INFLUENCING FACTORS FOR TOMATOES...

"... growth influencing factors (GIFs) to consider. The most important GIF is light. Artificial metal halide light can simulate full summer sunlight when daylight is at it longest. At maturity, tomato plants require a 16-18 hour photo-period to ensure maximum fruit production and an eight hour respiration period of total darkness. Gradually introduce your plants to higher light levels by moving the bulb closer to the plants by an inch or two every few days.

pH is the measure of alkalinity or acidity of the nutrient solution and is another very important GIF. If pH levels are not maintained at the appropriate level (pH 5.8 - 6.3 for tomatoes) nutrient deficiencies and toxicity will occur. Even seemingly small fluctuations in pH levels can result in inferior nutrient uptake by the plant. pH will need to be adjusted up or down based on the original reading of your water source. Potassium hydroxide will raise pH while phosphoric acid will decrease pH levels. Both products are available at your local hydroponic retail store. pH can be influenced by other factors and must be monitored regularly and adjusted as necessary.

Electrical conductivity (EC), measured in milliMhos, is the measure of electrical conductance of the total dissolved solutes (minerals) in the solution. The optimum EC range for tomatoes is 2.0 to 3.5 milliMhos. While EC measures the total dissolved minerals in a solution it does not identify the amounts of specific elements present. Therefore, it is easier to achieve the ideal EC using premixed 2-part hydroponic nutrient formulations than attempting to create your own formula using individual components.

Temperature is also an important GIF however, it is quite easily controlled. Tomatoes, like most plants grow best with a day/night temperature differential based on light or daytime perception. When there is light the plant considers it daytime and the temperature should be adjusted accordingly. The ideal daytime temperature for mature tomato plants bearing fruit is 18° - 25°C and nighttime is 12° - 18°C. An independent thermostat should be placed among your plants to ensure temperature regulation. An exhaust fan will help control temperature and provide air exchange.

http://www.hydrofarm.com/articles/factors_plantgrowth.php

http://www.simplyhydro.com/home_grow_tomatoes.htm

http://en.wikipedia.org/wiki/Ripening

Don't forget, for fruit to be ripened it also should first be fully grown.

Ethylene is, in fact, naturally emitted by fruit as they ripen, and by ripe or over-ripe fruit. This is the reason that 'fruit ripening bowls' which are covered, trap the ethylene and help to ripen the fruit more quickly.

The old trick is to put your green tomatoes or peppers in a paper bag with a ripe banana. The banana gives off plenty of ethylene, so the fruit quickly turns red.

Take a look at the spectrum for chlorophyll A and Chlorophyll B. You will find that UV is really not part of it. Leaves need red and blue light to activate photosynthesis. Some folk use red and blue LEDs but today they are too inefficient. High bright white LED with the correct spectrum of light out works the best for your $$ but they have to be close to the leaves.