Vapor Tube Lamp

—A vacuum tube lamp, a form of electric lamp depending upon the luminous properties of rarefied gases or vapor when an electric current is pa ed through them. Two principal forms of vapor tube lamps have reached succe ful development; the Cooper-Hewiit mercury-vapor lamp in which a column of mercury in | a gla tube is brought to incandescence by the pa age of an electric current, and the Moore light which depends upon the incandescence of rarefied gas, composed largely of air, contained in a gla tube of indefinite iength. Vapor tube lamps have a luminous efficiency of 25 or 30 per cent. which k far greater than the best arc or incandescent amps.