Fluorescent and HID (high intensity discharge) lamps require ballasts to apply starting voltage to the lamp and to establish current flow. Ballasts regulate current and power. Ballast types fall into two categories:

• Magnetic ballasts are often found in HID and older florescent fixtures. They are simple devices that are noisier and use more power than the newer electronic ballasts. Magnetically-ballasted lights can also have a noticeable "flicker
• 
  
• Electronic ballasts are lighter, smaller and quieter and offer more energy efficiency.