Chapter 4: Light
with the needed accesories
Plant growth involves the conversion of light energy into plant-building
materials (photosynthesis, see chapter 2). Two factors are important for
optimal growth. In the first place, the light intensity. Light intensity
is expressed in 'lumens'. At least 50,000 lumens are needed for growing
indoors. It's not sufficient to add up the number of lumens listed by the
manufacturer for each lamp. The total number of lumens given off is depends
strongly upon good reflection, and proper connecting fixtures and starter
ballasts for the lamps. The quality of the reflector used, and the connecting
fixtures and ballasts determine the light yield for the greatest extent.
For those reasons, self-built sets and home-designed illumination often
deliver a lot less light yield than lamps being used in professional horticulture.
We can improve the light yield in our grow room by applying reflective
material. We haven't painted the walls of the room matt white, and used
reflector caps for the lamps for nothing! The second important factor is
the wavelength of the light. For the production of chlorophyll, and an
optimum photosynthetic reaction, light from the blue spectrum (445 nanometers),
and light from the red spectrum (650 nanometers) is necessary. Blue light
ensures optimal phototropism. Phototropism is the phenomenon which causes
plants to grow towards the light, and to spread their leaves in such a
way to receive the most light.
4.2. Choices for lamps
In this book, we prefer high-pressure sodium lamps, and mercury-iodide
lamps for illumination. Ordinary light bulbs are not suited for cannabis-growing
due to their considerably short life span, and principally due to their
low light yield. Halogen lamps are not advisable for the same reasons.
Fluorescent lamps are not appropriate for home growing. They do serve well,
however, to stimulate seedlings and cuttings to set root. For actual growing,
we stick to gas discharge lamps in the form of high-pressure- sodium, and
mercury-iodide lamps. There are lamps being sold which emit both the wavelengths
needed (blue and red) but we prefer installing seperate lamps in a 1:3
proportion (1 lamp for blue light with 3 for red light). The combination
lamps give off a lower amount of lumens, since they have to emit different
wavelengths. This counts for growing: the more lumens, the greater the
yield. This doesn't mean we can install an unlimited number of lamps. Other
factors must be considered. Using many lamps means a higher temperature
(the heat must be discharged of), a greater need for fresh air (containing
CO2), and a greater need for water and feeding. Always remember the law
of minimums Depending on the size of the garden, we use 400 Watt lamps
or 600 Watt lamps. This choice is made in such a way that all the plants
in the garden area can be illuminated as evenly as possible. By using 400
W lamps, you can put up one-and-a-half times as many lamps for the same
electricity use as when using 600 watt lamps.Also 1000 watt lamps are being
sold but proper reflectors for these types of lamps are not available.
The result is a disproportionately large loss of yield. Moreover, 1000
Watt lamps give off more heat. Therefor they must be hung high above the
plants, and this means more loss of light yield plays in the question.
1000 Watt lamps, with respect to 400 and 600 Watt lamps, mostly cause pain
in your wallet, because the electricity bill gets higher.
In practice, it is possible to reach a light yield of 70-90% of the lumens
which are emitted. For that, (it can't be stressed enough), good reflection
is necessary. Below is a chart with data for several reflective materials:
Reflectivity in % - Reflective plastic sheet 90-95 - matt white paint 85-90
- semi-matt white paint 75-80 - matt yellow paint 70-80 - Aluminium foil
70-75 - Black paint less than 10 Using proper reflective material, proper
connecting fixtures ballast equipment, proper reflector caps with the lamps,
and a distance from the lamps to the plants of 40 to 60 centimeters, 400
Watt lamps deliver, on average, between 35,000 and 47,500 lumens, and 600
Watt lamps between 60,000 and 80,000 lumens (at a distance of 50-70 centimeters).
The distance between the plants and the lamps differs because 600 W lamps
give off more heat. Ifthe plants are to close to the lamps, they will dry
out and burn 600 Watt lamps are preferred, because you get the highest
light yield for the lowest electricity cost. Though they do require more
careful climate control The life span of a high-pressure gas lamp is approximately
2 years when it's used 18 hours a day. The lamps are, however, subject
to decay, which lessens the light yield.
In practice, it appears that high-pressure gas lamps give optimal results
for 4 to 5 harvests. After those, it's advisable to replace them. It seems
that the installation of one 600 Watt sodium lamp per square meter is enough
to achieve the best results. Principally one can say 'the more light, the
better', but with more illumination, the control of other factors (namely,
temperature control) becomes a problem. Indoor growers work with their
light source close to the plants. Considering the light yield of the sun,
(hundreds of thousands of lumens, but a little further away), fewer lumens
are needed for growing indoors. A simple formula shows that you can also
use three 400 W lamps for two square meters. The sodium lamps provide light
from the red spectrum. This light is used principally during growth. A
mercury-iodide lamp fills in the blue spectrum. For reflection, growers
use wide-angle reflectors with sodium lamps, and super-wide-angle reflectors
with mercury-iodide lamps. Super-wide-angle reflectors spread the light
over a greater surface area. We use the proportions of 3 red lights to
1 blue. So, the light from the blue lamp must be spread over a larger surface
4.3. Using high-pressure gas lamps
High-pressure gas lamps may only be used in the fitting meant for that
particular lamp type. High-pressure gas lamps all have their own start-up
conditions, voltages, characteristics, and shapes. Using lamps with improper
sockets can cause electrical shorts! Therefore, it's recommended that you
buy all the parts of a pressurized gas lamp from the same dis- tributor.
The sockets, ballasts, and connectors must always be protected from humidity;
otherwise, electrical shorts occur. As stated earlier, high-pressure gas
lamps have a long life span. You must be careful when replacing these lamps.
They are, as the name implies, under pressure, and they explode when you
destroy them. When you do that yourself, you must always wear gloves and
safety glasses. In addition, you have to protect yourself against the poisonous
materials found in these kinds of lamps. The heat given off by high-pressure
gas lamps, and their accompanying starter ballasts, must be completely
ventilated. This means that the lamps shouldn't hang too close to the plants
(hence drying and burning occurs), but also not too close to (flammable)
ceilings and walls. Place a piece of non-flammable material (not asbestos!)
between the lamp and ceiling or wall. Furthermore t's necessary to discharge
of excess heat by using a ventilator. Finally, it's important to keep high-pressure
gas lamps clean. Dirty lamps provide much less light yield than clean ones.
The lamps should be polished now and then with some glass- cleaning agent.
That should be done only when the lamps are turned off, and well-cooled.
the use of gloves to protect the lightbulb cloning accessories
Be especially careful with water. Lamps which are still hot, or even warm,
can explode when touched, and that's not funny Also, take care never to
touch these types of lamps with your fingers. Just like halogen lamps,
bodily acids can burn through, causing the lamp to fly to pieces.
4.4. Proper lighting for cannabis
The advantage of growing cannabis indoors is the fact that you can give
the plants the feeling that it's their flowering season all year round.
You're not dependent on the weather or the season. We distinguish two separate
phases in plant cultivation: the growth- or vegetative phase, and the flowering-
or generative phase. We've already made sure the lamps are installed in
such a way that all the plants can be optimally illuminated. A light period
of 18 hours and a dark period of 6 hours is ideal for the vegetative phase.
We're assuming that you already have cuttings with roots. With proper care,
a healthy cannabis plant can grow up to 5 centimeters per day. It's very
easy to cause the plant to flower. We only have to give the plants the
idea that the days are getting shorter ('autumn'; for cannabis, the sign
to flower). We do that by making the light and the dark periods the same
length; - 12 hours. In principle, cannabis is an annual plant. The entire
life cycle, from seed to death, takes place in one year in nature. When
growing cannabis under artificial light, it is possible to force flowering
earlier than in nature. After 4 or 5 days vegetative phase, flowering can
be 'provoked'. We do that the moment the clones have visibly started to
grow. Two or three weeks after the light period is reduced to 12 hours,
the plants begin to flower. It's very important not to interrupt the dark
period. If the plants receive light during the 12-hour dark period, they
'get confused'; they want to continue growing, and the blooming phase is
postponed. The generative phase lasts 60 days or longer, depending on the
variety you're growing. When working with cuttings, it's possible to harvest
four to five times a year.
the cutting or clipping of a clone and the motherplant and its clone on
a rockwool plug
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