Working with Metal Halide lights.

One important is that lumens are meaningless when it comes to growing plants.

Lumens are corrected for the human eye response for brightness, but plants don't need light that appears bright to us. 1 watt of optical output at 550 nm will appear much brighter to us compared to 1 watt of 670 nm light. A plant will have -more- use for that watt of 670 nm light output though: there are more photons per watt and only one photon can be used in photosynthesis.

Fine tuning the light will depend on the plant you are trying to grow, chlorophyls a and b have somewhat different absorption spectra. Optimizing light sources for this using LEDs is quite a business at the moment.

Blarg King said:

Oh I know how watts work. A 60 Watt incandescent gives off less light than say a 60 fluorescent. But for the purpose of this since it's all the same tyoe of light source a 1000 watt MH will produce more light than a 400 MH.

Fluorescent isnt really ideal. I believe MH and HPS give off more lumens per watt, not to mention to get a similar light spread and output from fluorescent would take a lot of fluorescent bulbs which means more fixtures and ballasts and more cost.

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I believe I can shed some light on this matter as I have a background in hort ED.
CFL ( Compact fluorescent esp. 3600 - 6500K values (6500K is daylight - white) are used to get plants to a beginning stage of their growth cycle normally. For growing in confined spaces they are used instead of MH/HPS as they produce far less heat. (lower fire danger). They are actually used quite a bit in crop production. Once the plants are large enough they are then transferred usually into a room with a combination of MH and or HPS/ or if lucky enough high power LED setup + Plasma "spot" lighting ( or a combo bulb set up) in addition to side lighting which can be either Hort fluorescence racks or even LEDs. This allows the plants to develop quickly with higher yields and simulate a nearly perfect growing condition.

CFL is not something to discount. For the entry level grower they're quite effective and plentiful.

Lumens are meaningless as Benm pointed out. µmol/J* or µmol s−1W*−1 is the unit used to measure effective spectra on plant growth.
Note: W* and J* indicates PAR watts and PAR joules (400–700 nm).

CFL's are fine or sprouting seeds and growing the first stages of a plant. At this point efficiency is not overly important.

Living in a country where hydrophonic cultivation of all kinds of produce is a significant source of income i hear and see what growers are actually doing. Sodium lights are pretty good to provide the bulk of light for most plants, but they need to be augmented with a bit of blue light from other light sources (mercury lamps or such).

There is a trend towards using LED technology as it's efficiency comes closer to that of sodium lights but the output spectrum can be chosen more narrowly. I presume LED lighting will become the standard for new greenhouses soon enough, if it isn't already.

Yeah Im using a T5 fluorescent grow light right now and I've use it for seedlings plenty of time its just not powerful enough for bigger plants. They have new sodium lights now that also contain a MH arc tube to provide the blue end of the spectrum all in one bulb.

I do think LED will definitely take over just right now the upfront cost is high enough that it would take a while for the savings of increased efficiency to return investment.

If you need a LOT of light that could work out better indeed. Commercial growhouses also use a combination of sodium lamps and something else for the short wavelenghts (metal halide, plain mercury).

Theoretical results are better for LED systems, but purchase cost can be a good reason to go for something else.

1000bulbs is great i used them for 2 12 volt slas a 6 volt sla lantern bat and a 24v 250 watt airplane light and 2 f15t8 germicidal florescent tubes.

Benm said:

CFL's are fine or sprouting seeds and growing the first stages of a plant. At this point efficiency is not overly important.

Living in a country where hydrophonic cultivation of all kinds of produce is a significant source of income i hear and see what growers are actually doing. Sodium lights are pretty good to provide the bulk of light for most plants, but they need to be augmented with a bit of blue light from other light sources (mercury lamps or such).

There is a trend towards using LED technology as it's efficiency comes closer to that of sodium lights but the output spectrum can be chosen more narrowly. I presume LED lighting will become the standard for new greenhouses soon enough, if it isn't already.

Click to expand...

Actually, I was just in Vancouver about a week ago and saw some High power LED lighting using Crees new-ish XLamp 3590 LEDs.
These were being used in an 4x 5 array format for doing mid-sized plants.