Artificial Lighting Question

Pretty pointless as plants need to be within inches of the tube to benefit. Might be good so you can see at night !

Pointless. If you need light at night use cheap flourescents. Plants need to be very close to the light in order to benefit properly. DiGiTAL ViNYL (no email) Zone 6b/7, Westchester Co, NY, 1 mile off L.I.Sound

Metal halides would be preferable. Three or four 400 watt units should evenly illuminate your space.

DiGiTAL ViNYL (no email) Zone 6b/7, Westchester Co, NY, 1 mile off L.I.Sound

I don't think a double bank would be adequate, but a ceiling covered with fluorescents would be enough for some plants at some stages of their growth. It would be prohibitively expensive for commercial greenhouses to do that; sunlight is free.

Andrew

They use incandescent lamps in greenhouses if they are just trying to lengthen the hours of daylight for plants that are sensitive to day length, because incandescents are cheap and they don't need much brightness. They use high pressuse sodium lamps if they need to supplement the amount of light. The natural light provides plenty of blue wavelengths to regulate plant growth, and HPS are more efficient and have better lumen maintenance than metal halide lamps. (that means they don't start dimming out after a few hundred hours.)

Best regards, Bob

Don't they supplement with halides when daylight hours are short?

But the heat output and cost factor could be prohibitive. MH lights get HOT and make the meter spin like crazy.

-- pelirojaroja

On a lumens per watt basis, metal halides win over flourescents. That's why I'm seeing them more and more often in commercial buildings. The only lights that beat them for efficiency are the high pressure sodium lights (the ones that look very orange); metal halides have a more natural-looking spectrum so win out over sodium for indoor lighting.

No, generally they don't. Triphospor T8 fluorescents with electronic ballasts can exceed that magic 100 w/l ratio. There are a *few* MH lamps that start out just as efficient (but not more efficient) but MH lamps lose their brightness fairly rapidly, while triphosphor flourescents maintain about 90% of their original brightness throughout their 20000+ hour life.

You're seeing them more often in commercial building because of the very high ceilings involved. Those are 400W lamps. It would take too many fluorescents to light a warehouse.

Low pressures sodium are even more efficient and look *much* worse. :-)

Best regards, Bob

I didn't say that. *I* said that MH lights were MORE expensive to run in comparison to fluorescents.

You're right; I was replying to what Pat said. I wasn't quoting you, but left your name in by mistake as part of quoting Pat's message. I should have editted it out, but didn't notice. Sorry for the confusion.

Best regards, Bob