This invention relates to an adapter for a discharge lamp. The adapter is particularly suited for use with a discharge lamp in which a discharge tube is disposed substantially in a plane and a lamp support housing is substantially surrounded by the discharge tube.
U.S. Pat. No. 4,241,386 discloses an adapter for a discharge lamp having a circular discharge tube, which surrounds a circular zone. The discharge lamp has a plug portion disposed on the peripheral region of the circular zone. Accordingly, this known adapter also comprises a socket portion matching the plug portion of the circular discharge lamp. The socket portion must be positioned in a peripheral region of the adapter in order to accommodate the circular discharge lamp.
Most mounting sockets receiving such circular low pressure discharge lamps (also called fluorescent lamps) have a socket portion which is situated in a peripheral area of the mounting socket, corresponding to the peripheral position of the plug portion of the circular discharge lamp.
U.S. Pat. Nos. 4,549,251 and 4,458,301 disclose a discharge lamp with a discharge tube where the discharge tube is bent in a shape so as to surround a substantially planar zone. The discharge lamp includes a lamp support housing. The lamp support housing is positioned in an substantially central area of the zone defined by the discharge tube. The lamp support housing comprises a plug portion with contact pins providing the electrical connection of the discharge lamp.
It would be desirable if discharge lamps of the type described in U.S. Pat. Nos. 4,549,251 and 4,458,301 were connectable to mounting sockets originally designed for circular lamps, i. e. for mounting sockets which have their socket portion in a peripheral area.
U.S. Pat. No. 5,471,375 teaches a mounting socket for use with a discharge lamp having a similar layout as those described in U.S. Pat. Nos. 4,549,251 and 4,458,301. The mounting socket comprises a socket portion matching the electric contacts of the discharge lamp, and also comprises a plug portion matching a known screw-type socket for incandescent lamps. Both the socket portion and the plug portion of the mounting socket are positioned in a central area of the discharge lamp when the discharge lamp is inserted in the mounting socket. However, when the mounting socket is placed in the screw-type socket of the incandescent lamp, and the discharge lamp is inserted in the mounting socket, the plane of the discharge lamp socket is above the level of the screw-type plug portion of the mounting socket. For this reason, a discharge lamp inserted in the mounting socket may interfere with the proper positioning of a lamp cover originally designed to cover a lamp inserted in the lower socket. Thus there is a particular need for a structure in which the level of the discharge lamp plug portion is not much higher than the plug portion of the mounting socket, and the plane of the discharge lamp is substantially the same as the plane of the original socket.
In an exemplary embodiment of the invention, an adapter for a discharge lamp comprises a socket portion suitable for receiving electrical contacts of a first discharge lamp. The first discharge lamp includes a discharge tube, which is disposed substantially in a planar zone having a principal plane. The socket portion has an associated socket contacting plane. The associated socket contacting plane is defined as the principal plane of the discharge tube of the first discharge lamp, when the latter is inserted into the socket portion of the adapter.
The adapter also comprises a plug portion which is insertable into an external female socket. The external female socket is of the type which is suitable for receiving a second discharge lamp, where the second discharge lamp has a discharge tube with a planar tube configuration. The plug portion of the adapter has an associated plug contacting plane. This plug contacting plane is defined by the principal plane of the tube configuration of the second discharge lamp, when the latter is inserted into the external female socket. The adapter further comprises a connecting portion for connecting the socket portion and the plug portion. The connecting portion provides a substantially rigid connection between the socket portion of the adapter and the plug portion of the adapter so that the socket contacting plane substantially coincides with the plug contacting plane.
The adapter is particularly suitable for discharge lamps which have a discharge tube surrounding a lamp support housing so that the lamp support housing is positioned in an substantially central area of the plane defined by the discharge tube. Such a lamp will be termed, folded lamp,, hereinafter because the ends of the discharge tube are folded inwards into the lamp support housing. The connecting portion of the adapter may be sized so that the plug portion is positioned in an substantially peripheral area of the plane defined by the discharge tube when the plug portion of the discharge lamp is inserted in the socket portion of the adapter. This allows discharge lamps with central plug portions to be used with mounting sockets and lamp housings which were designed for circular discharge lamps. Due to the fact that the plug contacting plane of the adapter coincides with the socket contacting plane, the principal plane of the discharge tube of the folded lamp will be practically in the same plane as the plane of the circular lamp. This means that the lamp covers originally designed for circular discharge lamps will be readily applicable with folded lamps as well.