You perceive heat contrasts, warm bodies, hot metal, cooling surfaces, even in total darkness. You can identify living creatures and recent tracks by temperature differences, but fine details, colors, text, and subtle features remain indistinct. Thick stone, metal, glass, heavy insulation, or uniform temperatures can block or confuse thermal vision. Magical darkness doesn't stop heat detection, but solid walls and barriers do. If range for Thermal Vision is unknown, and is needed, DN uses 60 feet as a default.