Equation for Parabolic Reflector

I am going to be building a hood/reflector soon, and I would like to create a curved hood that
will maximize the light reflection.  If I were to take a longitudenal cross section of the
hood, what would the optimum equation be for light reflection?  Is it a parabola, and if so,
is there a formula?  Any comments?

in Irving, TX with too much time on my hands (obviously).