Continued from “An Introduction to Light – Part 1″ …

It’s amazing (not to mention useful) to note that the brightness of your lights can determine the height of your plants.  A lot of light means small and thick-set plants. Less light means long and thin plants. The quality of the light (i.e. the presence of all light colours) is the key factor of good photosynthesis.

Some plants need a full twelve hour’s darkness in order to ensure abundant and full flowering heads – particularly during the first twelve days of the blooming period.  So it’s essential that these plants are left undisturbed.

Light and the direction of growth.

Light determines the growing direction of your plants. If the light comes from the right or the left and not from above, your plants will grow in this direction. However when there is an abundance of light plants dispose of measuring constructions – that is, they no longer compare the incidence of light on a part of the leaf to the other parts of the leaves.

Light gives information to the growth tips of plants. Blue light provides the impulse for the direction of growth because it is energy rich and has a short wavelength. Amazingly, this gives blue light the possibility to penetrate the substrate and provides the roots with information about the direction of growth too!

Thinking back to your school-days you may remember a certain experiment involving a potato.   (But then again, which experiment you remember depends on what sort of school you went to!)  A potato is put in a light-proof box and separated from the external world by two dividing walls. A hole is made in each wall and after a while the white sprout of the potato grows right up to the light, in spite of the fact that it was dark inside the box. When the white sprout reaches the light, the parts of the plant turn green and photosynthesis starts. The whole growth is not operated by photosynthesis alone but by another organ of the plant that is able to detect a few photons (light parts) and react. The potato has so much energy (starch = sugars), that it is able to take a meandering route through the box to reach the light.

Growing points (like the first point of the sprout) have ‘an eye’ for light flashes that we cannot see. Seedlings in the ground find their way to the light world in the same way.
Light – the bloom trigger

All blooming plants can be divided into three groups:

1. The first group contains plants that start to bloom independently of the length of the day and the night.
2. The second group contains plants that start to bloom as a certain length of day is exceeded, i.e.  when there are long days and short nights.
3. The third group contains plants that start to bloom if a certain length of night is exceeded.

Let’s explore this ‘switch’ or ‘trigger’ nature of light (as associated with the third group of plants). It’s interesting to note that plants in this group start to bloom if they experience at least twelve hours of darkness, without interruption, otherwise they simply keep on growing. At a certain rhythm of the day and night the legendary blooming hormone florigen is made. This hormone, that has never been isolated (so literally it’s unknown), is turned on and off by light.

Indoor growers know that switching their lights on for eighteen hours or more keeps their plants in a vegetative (rather than flowering) state. Under these conditions, the plant only produces leaves and stems, but no flowers. When the plant receives twelve hour’s darkness it begins to make blooming tissue in its axils. These little blooming points are called embryonic tissue. This early flowering period is more sensitive to interruptions of light than later on in the blooming period. It only takes a few days from switching the light on until the production of the first (embryonic) blooming tissue.  A mistake in this crucial first twelve days can ruin a harvest.

Interruptions in the daytime, like a power failure or bulbs that break, are not as disastrous. The plants will stop developing and the bloom will be later, but the biological clock will not be disturbed.

Interruptions of the night, on the other hand, can be disastrous. These interruptions can be very short but they will have huge consequences depending on the colour of the light. When the plant is disturbed at night with a light red colour it takes only a minute to confuse the plant and turns off the plant’s “switch” to bloom.  Research has found that disturbances in the middle of the night, say after six hours of darkness, have the worst consequences.  Even the light that shines under a door can be damaging. If the plants get no rest at night, they will not flower properly, or worse still, not flower at all. Later on in the blooming period, when the flowers have developed, a disturbed night’s rest will affect the crop, but the plants will keep blooming. This is because the transformation from growth to bloom has already been successfully achieved.

Outdoors, plants that have a full moon at the beginning of the blooming period need a lot more time to develop the blooming points than plants that commence the same process during dark, moonless nights.

Home growers claim that for these types of plants the best light conditions are a period of ten hours of light and fourteen hours of darkness. However, in spite of this many growers of resin-producing plants prefer an even split of 12/12.  With twelve hours of light we double the amount of resin production than if we use ten hours of light.

Well, that will do for now. Let’s hope that this has shed some light on the subject. Happy growing and blooming!