Brake light.

[Zero999]

What about a Black regulator style circuit?

They're so simple and efficient. You could build one regulator for each string of LEDs.

http://www.romanblack.com/smps/a04.htm

[Kalvin]

How about using four LM317 in TO-220 package connected as 0.35A constant current source, each feeding two LEDs in series?

[Zero999]

7 watts are way too much for a led brake light. You will blind everyone behind you!

I made to be the same as what a normal bulb is: 400 lumens.

I missed that.

Yes, it'll be too bright and not only because of the light distribution. Incandescent lights output that 400 lumens will do so over the whole of the visible spectrum, a lot of which will be filtered out by the red lens. The LED only produces light over a narrow bandwidth, which means it will be much brighter as the red filter won't block much of the spectrum.