Circuit regulation Question?

If I were to have a circuit, mainly containing lights (LEDs). They were all in parallel, are the amount on at any time wasn't constant. That is something 2 LEDs (1.4v) sometimes 1 (0.7v). How would i regulate the circuit as a whole, considering the voltage output needed it never constant. Which type of regulating circuit (Zener or IC) would be better in this case, why?