Refract & reflect subdivs. and photon map

[Numse]

I rendered a car model of mine and it took me 31 hours. The frustrating thing was that if I hadn´t rendered the glas on the lights it had taken about 4 hours. Someone know how I can speed up the render? I have 10 subdivs on reflections and 12 on refrections in my glas material.

One other thing. Whats the different between using irradiance and photon map on secondary bounces other than speeding up the render with photon map?

[Da_elf]

a: does your glass have glossyness to its refractions and reflections?
b: is this an exterior scene or something? if so then stay clear of photons

[Numse]

No glossy. Studio scene.