comparing Sodium and metal halide growth lamps

[merrill]

Does any one have comparitive information on Sodium vs. metal halide growth lamps encouraging blossoming as opposed to vegetative growth?   ANY info will be appreciated.

[Jeff zone 8 N.C.]

Merrill,  Iv'e used them on small palms and on valuable Clivia plants and they do grow plants well.  The Sodium lights are considered best for blossoming and Metal halide for vegetative growth. Iv'e always thought that a mix of the two would probably give the best light but the lights are expensive so I think most people chose the one they need. The Halide will give brighter white light (easy to read under them) and the sodium will give a more yellow, subdued light (very hard to read under them). They both are very low energy users compared to other lights. The light diminishes quickly with distance so put them as close to your subjects as possible, but the bulbs get hot so keep them a few inches away.  If your plants are fast growers you should be ready to move the lights up so the leaves don't get burned. They also produce a lot of heat so be ready to ventilate if in a closed space. One important thing. If the outer glass shell of the bulb gets cracked then throw the bulb away as it will emit dangerous radiation through the crack. Remember when watering to not let water splash on the bulb when it is hot. I may be wrong but I think you should also keep from touching the bulb because oils off your hands can somehow cause a hot spot on some types of bulbs and shorten their life.

[Jim in Los Altos]

Merrill,

Also consider mercury vapor lamps. They emit both uva and uvb. I've had really good results with the clear (versus frosted) reptile lamps. I keep a 150 watt clear mercury vapor light over the top of my 3 foot tall bottle palm for 10 hours per day while it's in the house December through February and it's currently pushing a new spear as fast as it does in mid summer. They cost around $40.00 and you need a fixture with a ceramic base rather than plastic because of the heat generated by the lamp. The heat is good, by the way, since my home is typically 68F but the bedroom with the bottle palm and lamp averages 72F and the lamp also directs heat directly onto the palm the way sunshine would.

[merrill]

Thank you, Jeff:

That's what the vendor said.  Thanks for the even more useful info.

Maybe I can help my Clivia, too.   How long did you use it each day, and for how long?  Sorry to ask so many questions.

Thanks, Jim:

As a matter of fact, have some mercury lamps w/ ballasts.  Always assumed they were useless for plant growth.  Going to have to do more research.

[Neofolis]

The mercury lamps are rarely used nowadays, as they are somewhat ineffiecient compared with the other two.  As mentioned, high pressure sodium is better for flowering, because it is mainly red spectrum, whereas metal hallide, being mainly blue spectrum is better for vegetative growth.  You shouldn't need a combination of the two, if there is still some natural light present, as natural light, because the sun has higher levels in the blue spectrum.  Don't bother with low pressure sodium, it is less efficient than high pressure and is even more biassed towards red spectrum.  Many manufacturers make versions of their high pressure sodium lamps, which are specifically designed as growlamps (Grolux, etc.) and have a slightly more balanced light than the normal sodium lamps, but they are still biassed towards red spectrum.  High pressure sodium has the best lumen efficacy, so gives you the most bang per buck in terms of running costs.

There are fittings available that will take two, four or six lamps, so you could use a combination to obtain a more balanced spectrum.   Another alternative is to use fluorescent tubes, which are available in a range of different colours including daylight (Colour:86/860).  The biggest problem with fluorescent tubes is that, whilst they are still very efficient, they take up considerably more space to obtain the same lumens output.  They do, however, have the advantage of instant startup and, because they run very cool, can be placed closer to the plants.

If you choose one of the high pressure discharge options, it is wise to use a digital ballast, rather than the usual magnetic ballast as it will enable almost instant startup, it will run much more quietly and it will give a more balanced output from the lamps throughout their lifespan, effectively extending the life of the lamps.