Dim headlights

Ive got a '76 911 that I recently upgraged its headlights to H5s. Upon installation, I noticed that my headlights are very dim. I pulled the bulb off and compared the output with a car with a similar 9004 bulb. I noticed that the other car's bulb was much brighter than mine. Is there a way to increase the light output on my car? Will I need to rewire and/or install relays for the light? Any help would be appreciated.
Thanks.