The luminance range that can be displayed on a theatre projection screen is the ratio of maximum to minimum luminance achievable during projection of film. The maximum achievable highlight is determined by light-source output capacity, projection optical efficiency, the transmission of minimum film densities, screen gain, etc. The minimum is the luminance contribution from house illumination and other stray light, plus optical flare raising black levels, and the transmission of maximum film densities. Measured values in typical first-run theatres show luminance ranges of 500:1 to 300:1 (usually limited by house illumination).