ELECTRODELESS BULB LAMP

The present invention relates to an electrodeless bulb lamp.

In our International Patent Application No PCT/GB2006/002018, dated 2 ^nd

June 2006 and now published under No WO 2006/129102, we have described and claimed an electrodeless bulb, the lamp comprising:

• a drive device adapted to drive at least two antennae;

• a ceramic wave guide; • at least two respective voids receiving the said antennae in the wave guide; and

• a central void in the wave guide, for receiving the bulb, equally spaced from the antenna voids, the central void having:

• a physical opening through which light can pass from the bulb and out of the wave guide.

In our British patent application No. 0610580.3, dated 30 ^th May 2006 and as yet unpublished, we described a lamp adapted to receive a microwave excitable, electrodeless bulb, the lamp comprising: • a microwave energy connector;

• a microwave bandpass filter having:

• its input connected to the microwave energy connector and

• an output;

• a wave guide having at least one microwave radiator, connected to the output of the microwave bandpass filter; and

• a receptor in the wave guide for an electrodeless bulb to be excited by microwave energy from the radiator, the wave guide being resonant in the pass band of the filter at least in presence of a said bulb.

The object of the present invention is to provide an improved electrodpless bulb lamp.

According to the invention there is provided a lamp adapted to receive a microwave excitable, electrodeless bulb, the lamp comprising:

• at least one microwave radiator,

• a solid wave guide having: • a receptacle for the or each microwave radiator and

• a receptor in the wave guide for an electrodeless bulb to be excited by microwave energy from the radiator, wherein:

• the receptor is at least partially tapered to provide a light path for light emitted laterally of the bulb to leave the wave guide.

Normally, the lamp will be provided in combination with a microwave excitable, electrodeless bulb received in the receptacle with an annular gap between the bulb and the wave guide at the taper portion of the receptor.

Measuring the radial extent of the annular gap at the orifice of the receptor in the waveguide in terms of the wave length of the microwaves propagated in the wave guide for excitation of bulb, we expect a gap of λ/10 to be possible without deterioration in performance. However, we prefer to use a gap of approximately λ/20.

Normally the taper will be at a relatively shallow angle to a central axis of the receptor, at least where the taper in the wave guide extends the full depth of the receptor, hi which case the taper can be at approximately 20° and preferably, typically at 10°or less to the central axis. Nevertheless steeper angles can be envisaged.

Alternatively, the taper can extend from part way only from the light emission side the wave guide, in which case it can be at a much steeper angle, for instance up to 60°, where the effective (or average) diameter of the receptor remains sufficient to couple microwave energy into the bulb. We would expect to provide a minimum of a 25% plain bore for a 75%, 60° taper bore. A more practical arrangement is expected

to be a 45° and preferably 20° half depth taper. 20° or less to the central axis , without - surprisingly - interfering with microwave coupling to the bulb.

Whilst other solid dielectric materials than ceramics having a dielectric constant greater than 1.0 are becoming available, we prefer to use ceramic material and in particular alumina.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side view of a lamp of the invention, in cross- section through a bulb in the lamp;

Figure 2 is a similar view of a modified lamp.

Referring to Figure 1, a lamp 1 has an electrodeless bulb 2, in a bore 3 formed in a ceramic wave guide 4 having a support plate 5. The bulb has a stem 2', which is thinner than the bulb, which engages in a bore 5' in the support plate for centring the bulb in the bore 3. For exciting the bulb, a microwave radiator 6 is provided in its bore 7 in the wave guide.

The bore 3 is tapered at 6° to its axis 8, which is normal to the faces 9 of the wave guide. The taper extends to the full thickness of the wave guide. This arrangement has been found to provide a significant increase in the amount of emitted light 10, being radiated from the bulb and wave guide couple.

In Figure 2, an alternative bore 11 is shown. This is steeper being at 15°, but extends to only half the thickness 12 of the wave guide. Again a significant increase in the amount of the radiated light has been noted.

In both cases the gap between the bulb and the ceramic at the opening of the taper is 3mm, which equates approximately to λ/20 for a 2.4 GHz microwave excitation via the radiator 6.