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 colour 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's 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 HID's 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's 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's. 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's 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 build up 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's 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 70's (practically nothing)