Not really. You could possibly use it on one or two low-light plants, although you might have heat problems. Halogen bulbs, right? You'd have to recharge every day, the bulbs will probably only last a couple of months, and that's going to work out expensive after a while. Get yourself a couple of compact fluorescent light bulbs from Lowes, something in the 20W-42W range. Brighter, cheaper, last longer, no recharging, use as few or as many as you need for your plants.

Thanks for the advice.
I have just finished a geenhouse using twin wall polycarbondate sheet; it is 14 x 6 (just the roof and one side wall - the other sides lean against the house). It is south-east location, so a little shaded at times.
I am thinking of using a high pressure sodium lights (1000 watt.) to supplement the light on cloudy days; I thought I wold add a re-chargeable light for a few plants which are more shaded.
In light of your comments, I will skip that.

Thanks.

Here's a little info about candlepowers, since 3 million sounds like a lot. Candlepower only describes the brightness of a light in a particular direction. Lantern advertisers focus their lights very tightly and then measure the brightest bit as some millions of candlepower (and then exaggerate a bit!). Nice for a flashlight, useless for plants. Lumens measures the total light output. Your 3 million candlepower lantern is probably producing about 2,000 lumens total, the same as a 30W compact fluorescent. The 1000W HPS will produce about 140,000 lumens.