LED Grow Lights - LED stands for light emitting diode and LED Grow Lights are made up of hundreds (or more) of these small semi-conductors! They are highly efficient, much cooler than HID Grow Lights and will use less energy!
Flueorescent / T5 - T5 Fluorescent Grow Lights are mainly used for growing seedlings and other indoor plants! They are extremely efficient!
HID Grow Lights - HID (High Intensity Discharge) Grow Lights have been around for many years. The reason they're called "high intensity" is because they discharge very bright light! Metal Halide (MH) and High-Pressure Sodium (HPS) are the most common HID Lights.