150 is a lot for a 12 but if you are looking to upgrade, just put it higher above the tank. Or you can or limit the light somehow (make a shade, run it less, etc.) I've never heard of anyone shading a light but if I was in your situation, I would probably go get some auto tinting. Keep in mind MH's are very hot so get something that can take the heat.
Or do what jakebtc said and get another tank.