You should be aware that your halogen bulbs are using nearly as much
electricity as regular incandescent bulbs, and most of the energy they
consume is being wasted as heat.
Fundamentally, the primary difference between a halogen bulb and a
regular incandescent bulb is that halogen bulbs have bromine or iodine
gas in the bulb rather than an inert gas like argon. The halogens
(bromine and iodine) react with the tungsten atoms that come boiling off
the hot filiment and redeposit the tungsten atoms back onto the
filiment, so that halogen bulbs don't darken with age the way regular
incandescent bulbs do. Also, halogen bulbs operate at a much higher
temperature so they use a quartz bulb rather than regular silica glass.
Still, you will realize a substantial electrical savings if you switch
to either compact fluorescent bulbs or LED bulbs. I would consider
compact fluorescent bulbs instead simply because their price is lower
and the price of LED bulbs is still coming down. LED bulbs are supposed
to last very much longer than CFL bulbs, so maybe LED is the way to go
to save more over the long term because you won't be replacing bulbs
nearly as quickly.