LIGHT- Cannabis Marijuana seeds Growing Guide
Indoors, 2000 lumens per sq. ft. is about as low as you
want to go indoors. If you get under this mark, plant growth
will certainly not go as fast as possible, and internode/stem
length will increase. Also, light distance to plants will be
much more critical. Daily adjustments to the lamps will be
necessary, meaning you get no vacations.
2500 lumens psf should be a good target, and 3000 is
optimal if your going to inject or enrich CO2 levels (more on
that later).
High Intensity Discharge lamps are the best solution for
most indoor growers. HID lamps come in 3 basic flavors: High
Pressure Sodium (HPS), Metal Halide (MH) and Mercury Vapor.
Metal Halide is an improved spectrum, higher intensity Mercury
Vapor design. HPS is a yellowish sort of light, maybe a bit
pink or orange. Same as some street lamps.
HPS lamps can be used to grow a crop from start to finish.
Tests show that the HPS crop will mature 1 week later than a
similar crop under MH, but it will be a bigger yield, so it is
better to wait the extra week.
The easiest HID to buy, and least expensive initially are
the flourescent and mercury vapor lamps. MV will put out about
8000 lumens per 175 watts, and 150 watts of HPS puts out about
15k lumens, so HPS is almost twice as efficient. But the color
spectrum from MV lamp output is not as good. HPS is high in
reds, which works well for flowering, while the Metal Halide
is rich in blues, needed for the best vegetative growth.
Unfortunately, MV lamps provide the worst spectrum for plant
growth, but are very inexpensive to purchase.They are not
recommended, unless you find them free, and even then, the
electricity/efficiency issues outweigh the initial costs
saved.
400 watt HPS will output around 45k lumens. For every 500
watts of continuous use, you use about $20 a month in
electricity, so it is evident that a lamp taking half the
power to output the same lumens (or twice the lumens at the
same power level) will pay for itself in a year or so, and
from then on, continuous savings will be reaped. This is a
simple initial cost vs. operating costs calculation, and does
not take into account the faster growth and increased yield
the HPS lamp will give you, due to more light being available.
If this is factored into the calculation the HPS lamp will pay
for itself with the first crop, when compared to MV or
fluorescent lamps, since it is easily twice as efficient and
grows flowers faster and bigger. Lamp Type Watts Lumens per bulb Total efficiency
Fluorescent Bulb 40 3000 400 watts = 30k lumens
Mercury Vapor 175 8000 400 watts = 20k lumens
Metal Halide 400 36000 400 watts = 36k lumens
High P. Sodium 400 45000 400 watts = 45k lumens
Notice the Mercury Vapor lamps are less efficient than the
fluorescent (FL), and can not be positioned as close to the
plants, so the plants will not be able to use as much of the
MV light. The light distribution is not as good either. MV
lamps simply are not suitable for indoor gardening. Use
flourecent, MH, or HPS lamps only. Halogen arc lamps generate
too much heat and not very much light for the wattage they
use, and are also not recommened, even though the light
spectrum is suitable for decent growth.
There is a new type of HPS lamp called Son Agro, and it is
available in a 250, 1000, and 400 watt range. The 400 is
actually 430 watts; they have added 30 watts of blue to this
bulb. It is a very bright lamp (53k lumens) and is made for
greenhouse use. These bulbs can be purchased to replace normal
HPS bulbs, so they are an option if you already own a HPS
lamp. The beauty of this bulb is that you do not give up most
of the advantages of MH lamps, such as minimal internode
spacing and early maturation, like most HPS users do, and you
have all advantages of a HPS lamp. One bulb does it all.
Internodal length of plants grown with the Son Agro are the
shortest ever seen with any type of lamp. Plants grown under
this lamp are incredibly bushy, compact and grow very fast.
Son Agro bulbs however, do not last as long as normal HPS
bulbs. There is something like a 25% difference in bulb
life.
Metal Halide (MH) is another option, and is available in
both a 36k and 40k lumen bulbs for the 400 watt size. The
Super Bulb (40k) is about $10-15 more, and provides an extra
4000 lumens. I think the Super Bulb may last longer; if so,
that makes it the way to go. Halide light is more blue and
better than straight HPS for vegetative growth, but is much
less efficient than HPS. It is possible to purchase conversion
bulbs for a MH lamp that convert it to HPS, but the cost of
the conversion bulb is more expensive than the color corrected
Son Agro bulb, so I would recommend just buying the Son Agro
HPS. Even though it costs more initially, you get more for
your energy dollar later, and it is much easier to hang than
10 fluorescent tubes.
If you have a MH 36k lumen lamp burning at 400 watts and a
53k lumen HPS burning at 430 watts, which is better efficiency
wise? Which will provide a better yield? Obviously, the Son
Agro HPS, but of course, the initial cost is higher. Actually,
the ballast will add about 10% to these wattage numbers.
The Son Agro bulb will prove much better than the MH for
any purpose. The MH bulb does not last as long, but is
cheaper. Compare $36 for a 400 watt MH bulb vs. $40 for the
HPS bulb. Add $15 for the Son Agro HPS. The HPS bulb life is
twice as long. 10k hours vs. 21k hours. The Son Agro is 16k
hours or so. Still, longer bulb life and more light add up to
more for your energy dollar long term.
Horizontal mounting of any HID is a good idea, as this will
boost by 30% the amount of light that actually reaches the
plants. Most HIDs sold for indoor garden use these days are of
this horizontal mounting arrangement.
HPS is much less expensive to operate than any other type
of lamp, but comes in the 70 watt size at the home improvement
stores. This size is not very efficient, but blows away FL in
efficiency, so they might be an alternative to FL for very
small operations, like 9 sq. feet or less. Over 9 sqr. feet,
you need more light than one of these lamps can provide, but
you could use two of them. 70 watt HPS lamps cost about $40
each, complete. Two lamps would be 140 watts putting out about
12k lumens, so it is better than FL, but a 150 watt HPS puts
out about 18k lumens, the bulb life is longer, bulbs are
cheaper and the lamp more efficient to operate. The biggest
problem is that the mid size lamps like the 150 and 250 watt
HPS are almost as expensive to buy as the larger 400. For this
reason, if you have room for the larger lamp, buy the 400. If
your going pro, a 1080 watt model is available too, but you
might find there is better light distribution from two 400
rather than one large lamp. Of course, the two smaller lamps
are more expensive to purchase than one large lamp, so most
people choose the larger lamp for bigger operations.
Heat buildup in the room is a factor with HID lamps, and
just how much light the plants can use is determined by
temperature, CO2 levels, nutrient availability, PH, and other
factors. Too big of a lamp for a space will make constant
venting necessary, and then there is no way to enrich CO2,
since it is getting blown out of the room right away.
Bulb Costs: the bulb cost on the 70 watt HPS is $24, the
150 is only $30, and the 400 is only $40. So you will spend
more to replace two 70 watt bulbs than you will to replace one
400 watt HPS. (Go figure.) Add that up with the lower resale
value on the 70s (practically nothing) and the fact that they
are being modified and are not suited to this application, and
it becomes evident that $189 for a 250 HPS lamp, or $219 for a
400, might just be worth the price. Keep in mind that for $30
more, you can have the larger lamp (400watt) and it puts out
20k lumens more light than the smaller lamp. Not a bad
deal!
Here is the breakdown on prices (from memory): Type Complete Cost Bulb Cost Bulb Life Lumens
HPS 400 $219 $40 18k hours 50k
MH 400 $175 $37 10k hours 36k
Son Agro400 $235 $55 15k hours 53k
Super MH400 $190 $45 ?? 40k
MH 250 $149 $32 ?? 21k
HPS 250 $165 $36 ?? 27k
HPS agro250 $180 $53 ?? 30k
MH 150 $139 $25 ?? 14k
HPS 175 $150 $30 ?? 17k
If your looking for these types of lamps, look in the
Yellow Pages under gardening, nursuries, and lighting for
indoor gardening stores in your area.
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