A lighting ballast controls and regulates the electrical current that runs into a bulb. HID lights (MHS and HD) require a ballast to start and stay lit. Without a ballast, the amount of electricity going into the HID bulb will vary, and the bulb will short out. The ballast for an HPS or MH light is in its own rectangular metal box that is separate from the bulb area.

CFLs are "sell-ballasted"--that, is they have a ballast at the base of the bulb. The bigger the CFL, the bigger the ballast will be. Check out the base of a 125w CFL. It's huge...it often has small vents on it. That's to keep the ballast inside from overheating.

It sounds like you're just getting started in growing. I have made the same suggestion on several different threads to other people. If any of this is too simple for you, sorry...just trying to get the information across. This is, IMO, the best, cheapest, and easiest way to grow 1-2 plants.

Get two 10" clamp lights at WalMart for $10, and get three Y-Adaptors for each of the lights (about $1.50 each). Buy four 26w Daylight CFLs (around $10 total). Starting with one of the clamp lights and one Y-adaptor, veg four plants in 16 ounce Red party cups. Daylight CFLs are ideal for this...keep them an inch or two from the plants, and have them on between 18 and 24 hours a day. (Different people prefer different amounts of light during the beg period.) As the plants get larger--past about 2 inches in height--transplant them into 5 or 6 inch square pots, and add two Y adaptors to the one you have in your clamp light. You can now use all 4 Daylight CFLs to keep vegging your plants.

When your plants are about 6-8 inches tall, transplant them into 3 gallon pots. But four more Daylight CFLs and make a second clamp light with four lights. Keep vegging until your plants are 10 inches tall, and then switch your daylight CFLs for 23w to 26w Warm white CFLs (about $10 for four) and "flip" your lights to 12/12. After a week or so, your plants will show signs of sex (check other threads on here for how to determine that) and you can throw out the males and concentrate on your females. Using Warm White CFLs, you can flower your plant until harvest. One of those clamp lights with four bulbs is fine for one plant; if your plant is tall (over 24"), you might want to use the other light to give some side lighting. CFLs aren't so good for canopy penetration. One clamp light with four bulbs can flower a plant well; this set up of two lights/eight bulbs will double that. You'll end up with a nice 22-30" plant or two.

Total lighting cost

Two clamp lights--$20
Six Y-adaptors--$10
Eight Daylight bulbs--$20
Eight Warm White bulbs--$20
TOTAL--$70