Dear Sev, first of all, a simple thing. Light in the vacuum always moves by the speed 299,792,458 meters per second: this fact is exactly true because of the modern definition of one meter. The speed of light in the air is just 0.03% smaller than the speed of light in the vacuum. Nothing ever travels faster than light in the vacuum.
Second, mirrors typically reflect less than 100% of coming light - something like 70%. But that's not the main problem here.
Third, the energy is conserved, so you can't produce much more "light" by putting mirrors. You can't illuminate 100 households by having 1 light bulb and "copying" it by mirrors. Why not? While you may increase - and almost double - the "amount of light" that is hitting a particular area, this fact is (more than) balanced by the fact that the light that would be absorbed by the area occupied by the mirror itself is not absorbed.
So when it comes to the energy budget, ideal mirrors (that reflect 100% of light, just for the sake of simplicity) only rearrange the distribution of light - which areas finally absorb it and which areas just reflect it. The total amount of light that is absorbed is given by the total amount of light that is emitted on the light bulb - and it only depends on the light bulb (and its power).
If you consider light as a "practical thing allowing us something to to be seen", then you want the light to be reflected, e.g. by a book. But the counting for a book that reflects some light - so that we can read it - is similar as the counting for an object that absorbs the light. Mirrors may increase the amount of light reflected by a particular book, but they may not increase the amount of light reflected by the whole room, assuming it has a uniform albedo.
If you look at a light bulb and a nearby mirror, you may see "two light bulbs" and a doubled amount of light, so to say. But this is only true from certain directions. From other directions, the outcome is different and often opposite. For example, if you place your eyes behind the mirror, so that the light bulb is on the opposite side of the mirror than you, then you see no light bulb directly - and no unreflected light from a light bulb (and no light bulb light reflected only by mirrors).
This lesson is much more general. Mirrors - and any other gadgets - may move energy from one place to another, or transform it from one form to another. But they never change the total amount of energy.