Technology : the electric current runs through a filament and heat it. The filament becomes consequently incandescent and creates light and heat.
The incandescent lamp are now clear (that means you can see the filament in the bulb when you switch off the light). The frosted or opalescent bulbs are not available anymore because considered as "energy-consumer".
The incandescent system can be used with a dimmer system.
You can easily replace them by halogen or fluocompact bulbs (energy saving lamps) - Warning : Energy saving lamps are not necessarily the best choice.