Are you waiting long enough for the bulb to ignite?
The capacitor needs to charge first.
If it's humming, you wired it right.
Is the bulb screwed in snugly? Sometimes those big sockets can be tough to screw into the first time. Be gentle but firm.
The ballast may take up to a minute or 2 to charge and ignite the bulb.
stinkyattic Reviewed by stinkyattic on . MH help I bought a 400 watt metal halide industrial type light. U know the ones that hang in like a warehouse or lowes. But anyway i hooked it up green to green white to white and black to black. Plugged it in and nothing. I can hear a low level buzzing from the ballast but the light bulb doesn't light up. Even bought a new bulb and nothing. Someone plz help. Rating: 5