How many Amps in a Garage. AND how to maintain consistent lighting from an outlet (no flickering)
More current! What are you using for lighting - arc lamps? 

As an animator and photographer myself I'd want to run the lighting as cool as possible. There are some great LED lights out there (or you could build your own). For small stages I've even used LED torches for highlights.

LEDs also have the advantage of running from a regulated DC supply (which gets around your droop problem). You can control intensity (PWM) and color temperature control (LEDs come in all sorts of colors). 

Modern digital cameras (video and still) operate quite happily in lower light conditions giving well saturated color. 

Just on a Health and Safety point

(1) Drawing a higher current than the wiring was designed to take greatly increases the risk of fire. You really do not want to cause a fire. The fact that your lights dim means that the system is straining to cope with normal demand.

(2) Hot lights can also cause fires. Especially with various artist's materials being used (bits of paper, paint etc.)