A PA34-200 on an IFR flight plan in VMC conditions was being vectored for an ILS; but accepted a runway change because of the improved visibility. During the vector the reporter deviated from his assigned altitude because he forgot that he was still IFR.

Narrative

I was approaching CRW under Approach control; vectors for ILS Runway 23. The weather opened up and Controller asked if I'd like to try Runway 33; since that would be more favorable for the wind. Controller gave me an altitude of 3000 FT and told me to turn for the airport and let her know when I spied the field. I was pretty low at 3000 FT and could not see a long way; although visibility was excellent. Controller did not clear me below 3000 FT; but I saw what I thought was the runway and erroneously headed in. Controller received an altitude alert and called me at 2400 FT and I immediately climbed back to 3000 FT and approached uneventfully. What I had seen was not the runway. The visibility was excellent and I had clear ground in sight at all times without haze or cloud; so I never felt uneasy or in any danger of ground contact. Nevertheless; I was not cleared below 3000 FT. When Controller turned me toward the airport; I suppose I 'went visual' and the result was an altitude deviation. This is not a complicated problem; just follow the clearance. I learned that at only 2000 FT or so AGL distances are stretched. I could not believe how far away 8 miles turned out to be from that altitude. What I thought was the runway and runway end lights turned out to be reflections from the sun (into which I was flying) on roadside objects. That is a lesson to be taken from this as well. Large airports (this is the first time into CRW for me) always surprise me with how much land they occupy.