It's probably fine, but having 6 lightbulbs on 1 shitty extension cord just screams fire hazard to me.
I have 1 - 150W 7500lumen 5500k+2 13W 6500k 900 lumen bulbs with 1 big clamp reflector and 2 smaller ones on each plant, probably about 2-3 inchs away, if you have the room. give them as many...