AbstractSmoke‐obscuration of monochromatic (0.632μm) light helium‐neon lasers and of broad‐band continuum light a hot tungsten filament is reported. The effect of forward‐scattered light is evaluated for the monochromatic source, and the degree to which the Bouguer law is obeyed for a non‐monochromatic source is discussed. Practical experience with both small‐scall and fire experiments