Fluorescent lamp with superimposed luminescent layers

Electric gas 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 a luminescent screen which comprises a light-transmissive support on which two superposed luminescent layers are disposed each of which layers on excitation by the radiation emanating from the discharge emit light, the layer which faces the discharge consisting of a luminescent material which per unit weight is more expensive than the material of the other luminescent layer, characterized in that the fraction p of the total amount of radiation emanating from the discharge which is converted into light by the luminescent layer facing the discharge lies between the values 0.80 and 0.99 and that the chromaticity of the light emitted by both luminescent layers together deviates less than 3.5 CIE units from the chromaticity of the light emitted by the luminescent layer facing the discharge.