Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Declared Emergency
Aircraft
In cruise flight at 15;000 FT the Cabin Press warning light illuminated. We decided to declare the emergency and executed an emergency descent; final descent was to 8;000 FT then the light extinguished. Then we were assigned 6;000 FT; cabin pressure was now below around 7;000 FT; we did the checklist and advised ATC of our intentions to proceed to [nearby airport].  At the same time we got a hold of Dispatch and told them we declared an emergency with ATC and that we were diverting; then in coordination with Dispatch we determined that the best course of action was to return to [departure airport]. We were assigned 4;000 FT since we needed to burn fuel to not land the airplane above the landing weight limitation.In the cabin the passengers and Flight Attendant were okay and none of them experienced any difficulty; they were also informed of the diversion; we burned the fuel and landed normally and safely.
Dash 8 Captain reported loss of cabin pressure at 15;000 FT; the crew declared an emergency and returned to departure airport.