PURPOSE: To increase the amount of phosphor powder depostion without causing uneven depostition layer by a method wherein high voltage for electrostatic coating is applied across a galss tube heater and phosphor jetting nozzle which is inserted into the glass tube and having at the nozzle tip a powder disperser and an electrode.

CONSTITUTION: A glass tube 1, while being rotated with an insulative rotator 2, is heated by burner 3. Into the glass tube 1 a phosphor powder jetting nozzle 4 is inserted, and a high-voltage generator 7 supplies a voltage of 10W25kV across the nozzle 4 and the burner 3. At the same time a phosphor powder feeder 5 supplies powder phosphor to the nozzle 4. The powder is jetted from the tip 6 and electrostatically coated on the internal surface of the glass tube 1. The tip 6 of the nozzle 4 has phosphor powder jetting holes 8 and further ahead a conical porcelain disperser 10, and an electrode 12 consiting of the first part 13 of a 0.1W3mm in diameter and 3W50mm long wire extending in the direction of nozzle axis and the second part 14 located at a minimum of 3W10mm from the internal surface of the glass tube 1.