NO! Not safe!!!

Do a search here and look into CFL's (compact fluorescent lamps). The really big ones are fairly expensive, but not as bad as metal halide, and they don't need a ballast.

False economy. If you need enough power to want a metal halide (250W and up) then you should stump up and buy a metal halide. Compact fluorescents are barely half as efficient and so you will be paying twice as much on your utility bill. Nice to save $100 up front (remember you would need about 400W of compact fluorescents to get the same light as a 250W metal halide), not so nice to pay an extra $15 every month that you use it. Below about that 250W level, metal halides are less efficient and you will be better getting a compact fluorescent if you need a single intense light source. Straight tube fluorescents are more efficient than compact fluorescents and you should use those if you need between about 80W and 400W of light and can get the required intensity with them.

Metal Halide light system is expensive, because they are worth it.
but if you have patience to shop around, it can be very reasonable.

I got a new 400w MH electroic ballast plus a bulb all for $50.00 on ebay. I spent another $10 for parts and made myself a fixture. Because it's an electronic ballast, it can fire both MH or HPS bulbs.

This system made a huge difference in my seed starting efforts.

dcarch

I have a couple metal halides for my basement, and the difference between those and flouro's are is amazing. Flouro's will keep them growing nice, metal halides will will make them flourish and take right off. If you have the money to spend, go for it, you wont regret it.....that is what I did. I still have some plants under flouro's on my main floor, but my high light ones are in there with the metal halides.

I have a passion vine, that I brought in from summer, the frost got it twice. I took a few cuttings and stuck the plant under the MH's, and now, a few weeks later, it is beautiful. It is getting ready to flower again, the leaves are deep lush green. It is nicer in my basement that it was outside, because there are no "elements" to damage it.

HTH let us know what you decided

you need to look for cheaper sources in my opinion. check out http://www.insidesun.com/index.php

good folks there with high quality and cheap prices. there you can get a 400 watt hps or MH for around $120.

i wouldn't even think about using compact floro bulbs cuz they aren't going to put out the power you need.

also i was wondering how many square feet you need to light. usually a 400watt covers 4'x4' , a 600 covers 6'x6'-8'x8' , and a 1000 watt covers 8'x8' - 10' x 10' area. so keep that in mind when selecting lighting.

Thanks for the advice! I don't know why I hadn't thought of Ebay. I went on there and ended up getting a 400watt light with reflector and ballast for about $80. My plants are much happier now.

Thanks.

(mr. nice guy) usually a 400watt covers 4'x4' , a 600 covers 6'x6'-8'x8' , and a 1000 watt covers 8'x8' - 10' x 10' area.

(Lermer) Normally, you want to go horizontal in order to get as much direct light as possible. The light footprint is rectangular, and from end to end you get only about a 3' width. From side to side you get 4'-6' depending on reflector type. That is with a 400w.

Increasing the wattage does increase the horizontal coverage, but not the vertical coverage (which is limited by the canopy which blocks light to lower leaves). However higher wattages mean fewer points of light and more shadows on leaf surfaces.

Quartz metal halide (MH), and HPS, are hopelessly obsolete. I recommend either ceramic metal halide (CMH), or pulse start metal halide (PSMH). Fluorescents are fine for cuttings.

Eventually LEDs might be efficient, but by then probably something else will come along. I'm excited by the new 25 watt CMH with parabolic reflector bulb. At about one foot, there are 4300 foot candles (optimum). At about two feet, there are still 1000 foot candles (adequate). I would recommend many of the 25w CMH bulbs, but the problem is the high price on this new patented technology.

Low power HID lamps are extremely inefficient. The little 25W reflectors are less efficient even than the small spiral CFL bulbs, and only about half as efficient as a good straight fluorescent tube or a high power metal halide bulb. Don't consider using them as a plant light unless you don't mind the $100 price tag (for one 25W bulb!), the short lifetime, and the terrible lumen maintenance. These bulbs are designed for specialist applications where a small intense light source is needed for accent lighting, with the ceramic technology providing better colour rendering for retail applications, etc.

The 25W PAR CMH has 1220 lumens, or 48.8 lumens per watt.
This is comparable to the 45-60 lumens per watt of a comparable wattage compact fluorescent:

http://en.wikipedia.org/wiki/Luminous_efficacy

The price is higher, but the CMH (with PAR reflector built into the bulb)reflects better because the arc tube is almost a point source and it is horizontally oriented.

Without a parabolic reflector built into the bulb, the compact fluorescent radiates in almost every direction, and is not directed toward the plant.

You are quoting random rubbish from the internet again without checking what is happening today in the real world. I doubt you can find a CFL in Home Depot or any other store in any state of the union, and probably not in an internet store either, which produces anything more than a lumen or two away from 65 lumens/watt. There are however, a number of compact fluorescent designs which considerably exceed this efficiency, mostly high power devices with relatively few bends. You continually compare your infamous CMH bulbs with obsolete technology, presumably for greater impact on your sales targets, but it is highly deceptive. Please compare best practice CMH technology with best practice technology of other bulb types.

The PAR CMH does indeed produce a highly focussed beam just like the halogen reflectors it is designed to replace, but this property is of only limited value for growing plants. In fact most growers strongly prefer a more diffused light to allow maximum intensity without localised scorching. Some form of reflector, baffle, or enclosure is important to getting maximum light from any bulb onto the plants. Some CFLs come with an integrated reflector, some don't, but something should always be used for plants. A simple device like a white card baffle surrounding the area is extremely effective.

And what is this about horizontally oriented. It is oriented whichever way you plug it into a socket. It is in fact vertically oriented with respect to the reflector, a choice which is equally as effective as any other orientation when combined with an appropriate reflector shape. In this case, the vertical orientation with a round reflector gives a symmetrical beam spot, highly desirable for this type of bulb.

You may also wish to consider the lumen maintenance of both the 25W CMH and a typical domestic type CFL. Both are pretty awful to be honest, which greatly limits their usefulness as plant lights. For example, the CMH loses over 30% of output before 5,000 hours of use. You would really want to be replacing them on something like a 2,000 hour cycle, pretty scary at $90 a time.

Lifetime/maintenance curves based on light type