The invention relates to an electric lamp comprising
a light source provided with a discharge vessel which is sealed in a gastight manner and which transmits radiation,
a lamp cap having a shell and a base,
a housing connected to the light source and to the lamp cap,
ballast means which are electrically connected to the light source for operating the light source and which are arranged at least partly in a space surrounded by the housing and the lamp cap, and
contacts which are connected with electrical conduction to the ballast means at least during lamp operation, one of said contacts being provided on the base and a further one on the shell.
Such an electric lamp is known from European Patent Application 156439. The known lamp is designed for use in the same applications in which traditionally an incandescent lamp was used. A major advantage of the known lamp over an incandescent lamp is that the luminous efficacy of the known lamp is considerably higher than the luminous efficacy of an incandescent lamp. A disadvantage, however, is the fact that the length of the known lamp is greater than that of an incandescent lamp, so that the known lamp is less suitable as a replacement for an incandescent lamp in some applications. It is accordingly desirable to reduce the length of the known lamp in order to increase the range of application of this lamp. A further reduction in the length of the lamp, however, is often accompanied by a size reduction of the housing, whereby the capacitive coupling between the ballast means often present in the housing and the contacts on the lamp cap increases. This capacitive coupling increases even further when the ballast means are partly provided in the lamp cap in order to facilitate a further size reduction of the lamp. The ballast means may consist, for example, of a coil when the electric lamp is operated with a current whose frequency is identical to that of the mains voltage with which the lamp is supplied. In that case there is a low-frequency lamp operation. Alternatively, however, the ballast means may comprise a circuit arrangement for generating a high-frequency current from the mains voltage, with which the electric lamp is supplied, for operating the electric lamp. In the latter case there is a high-frequency lamp operation. The frequency of the high-frequency lamp current is often of the order of 10 kiloHerz. Owing to the increased capacitive coupling between the ballast means and the contacts of the lamp cap, the ballast means cause a comparatively high degree of interference in the supply voltage mains during lamp operation, especially when the electric lamp is operated at a high frequency.