point is within the e c e requirements in case the discharge lamp was operated by means of a dc current with a substantially constant amplitude the amplitude of the dc current was 10 15 and 20 ma and the corresponding colour points are indicated as dc 10 dc 15 and dc 20 respectively in case the discharge lamp was operated with a ac current having an rms value of 10 15 and 20 ma respectively the obtained colour points ac 10 ac 15 and ac 20 are outside the region corresponding to the e c e requirements in fig6 b the luminous flux u03c6 of this discharge lamp for both dc and ac operation is plotted as a function of the rms value of the lamp current it can be seen that the luminous flux obtained by dc operation is substantially higher than the luminous flux obtained by ac operation it can therefore be concluded that dc operation offers substantial advantages over ac operation both in terms of luminous flux as well as in terms of the position of the colour point furthermore dc operation can be realized using relatively simple means and causes no or only a very small amount of electromagnetic interference in fig7 fig7 a is a front elevation of a lighting unit according to the invention fig7 b is a side elevation of the same lighting unit la is a discharge lamp bent in a plane and provided with a gas filling consisting of neon the discharge lamp wall is provided with a luminescent layer lu h is a housing with a rectangular aperture a mirroring reflector r is provided in the housing forming the reflecting surface in this embodiment the rectangular aperture of.