Light Transport; Low Wing; 2 Turbojet Eng
Flight Crew Instrument
Flight Crew Total 2800
Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
General None Reported / Taken
Airport; Human Factors
Taxi from the FBO ramp to Runway 04. Normal taxi is to the end of the taxiway to the runway.  This particular runway design has Runway 04 partially down the taxiway. Accidently crossed 04. The runway hold lines should be repainted. I suggest in ground hold lights should be installed at this holding point prior to reaching Runway 04.
Charter pilot failed to note the Runway 04 hold short lines at HOU and taxied onto the runway without clearance.