Luminescent coating for low-pressure mercury vapour discharge lamp

A low-pressure mercury vapour discharge lamp having a vacuum tight radiation transmitting envelope comprising a quantity of mercury and a quantity of rare gas and provided with electrodes between which the discharge takes place during operation, and with a luminescent coating comprising three luminescent materials, a first material having an emission band at a maximum in the wavelength range between 430 and 490 nm and a half value width of less than 100 nm, a second material mainly having its emission in the wavelength range between 520 nm and 565 nm, and a third material mainly having its emission in the wavelength range between 590 and 630 nm, wherein said second luminescent material is activated by terbium and is selected from the group consisting of materials defined by the formulas:

• Ce.sub.1-x-y La.sub.x Tb.sub.y MgAl.sub.11 O.sub.19 and a
• (Ce.sub.1-x-y La.sub.x Tb.sub. y).sub.2 O.sub.3.sup.. nAl.sub.2 O.sub.3 b
• in which
• O .ltoreq. x .ltoreq. 0.50
• 0.20 .ltoreq. y .ltoreq. 0.50
• x+y .ltoreq. 0.90
• 10 .ltoreq. n .ltoreq. 12
• and in which up to a maximum of 25 at% of aluminum may be replaced by elements selected from the group consisting of gallium and scandium and in which magnesium may at least in part be replaced by one or more elements selected from the group consisting of zinc and beryllium.