Low-pressure mercury discharge lamp

Abstract

A low-pressure mercury discharge lamp with a very good color rendering and with a color point (x.sub.L, y.sub.I) on or close to the Planckian locus, includes a gastight, radiation-transmitting envelope which contains mercury and rare gas, and a luminescent layer including a first luminescent material activated by bivalent europium and having an emission band whose maximum lies between 470 nm and 500 nm and whose half-value width is at most 90 nm, a second luminescent material activated by bivalent manganese and having at least an emission band mainly in the red region of the visible spectrum, a third luminescent material with a band emission whose maximum lies between 430 nm and 490 nm, a fourth luminescent material with emission mainly between 520 nm and 565 nm, and a fifth luminescent material with emission mainly between 590 nm and 630 nm. As compared to a lamp with only the first and second luminescent materials, the addition of the third through fifth materials considerably increases the luminous efficacy of the lamp while the very good color rendering is maintained, and the speed with which the luminescent layer is degraded during lamp life is considerably reduced.

Dependencies are inferred from the claim text.