Just FYI, for $100 per light you can switch to 48" T5 HO lights with 2 lights in each one. I did this with my lights. I had 4 250W wallpacks in each SS bay. I replaced them with 4 new fixtures. Two are always on and I put the other two on occupancy sensors. Now, I have two lights on all night which put out as much light as my 4 old fixtures put out and when someone pulls in the other two lights kick on and make it extra bright for the customer.
In addition to saving a ton on electricity, I am saving a fortune on light bulbs. The T5 bulbs use 54W per bulb or 108W per fixture. The do not get any dimmer over their life like the metal halides. New bulbs are $3.50 each.