GB2034453A - Beacon lamp - Google Patents

Abstract

A beacon lamp has a drum-shaped lens member (12) the focus of which is at the central region (18) of the drum cross-section, a U-shaped Xenon discharge tube (20) lying in a transverse plane of the drum and being symmetrically positioned about the centre of the drum. The drum has top and bottom opaque cover members (26, 28). The lens is faceted (14) to reduce its thickness. The lamp has a radiation distribution which makes it particularly suitable for use on road vehicles. <IMAGE>

Description

SPECIFICATION Improvements in light sources This invention relates to light sources, and particu marly to a light source of the type known as a beacon lamp which is designal to provide a beam of light over a wide angle about an axis.

Flashing beacons used as warning lights for different purposes will have a defined light beam pattern specified to meet a particular requirement. For example, a flashing light on an emergency vehicle must be visible through 3600 and the vertical beam spread kept small to achieve a high beam intensity.

Similarly when the lamp is used in a fixed position, the angle of the light beam is usually kept narrow in the vertical and restricted in the horizontal, as for example with the beacon lamp described in British Patent Specification No. 1,383,653 for use on airfields.

There are certain advantages in using an electronic xenon flash tube to produce light flashes, since the peak intensity of the flash can be high. Also the luminous efficacy can be higher than from a tungsten filament lamp, which is used in a rotating lens or reflector system to produce a rotating beam giving an effective flash of light.

This invention is concerned to provide a light source of the beacon type which provides a particularly advantageous form of radiation pattern and which nevertheless is relatively simple in construction.

According to this invention there is provided a light source comprising a drum-shaped lens member the focus of which is at or near the central region of the drum cross-section, a U-shaped discharge tube within the drum-shaped lens member lying in a transverse plane of the drum and substantially symmetrically positioned about the centre of the drum, and top and bottom cover members for the drum member.

Preferably the drum-shaped lens member is faceted to reduce its thickness. The discharge tube is preferably a xenon flash tube, and can have its electrical connections passing through one of the cover members. The drum lens and cover members pref erably form a weather-tight enclosure.

The invention will now be described in more detail by way of example, with reference to the drawing, in which: Fig. lisa cross-sectional elevational view through a beacon lamp embodying the invention; and Fig. 2 is a plan view of the lamp taken on the line 2-2 in Fig. 1, showing by the line 1-1 the section on which Fig. 1 is taken and also having superimposed thereon a plot of the radiation intensity plot in the horizontal plane.

The light source or beacon lamp 10 is seen to comprise a cylindrical drum-shaped lens 12 of clear plastics material and which is circularly symmetrical, and in section is faceted as shown at 14 to reduce the total lens thickness. The effective optical shape of the lens is indicated by the dashed lines 16 at the left-hand side of Fig. 1. The lens focus is at the centre 18 of the lens.

In normal use of the lamp the drum axis will be vertical and the transverse plane of the drum will be the horizontal plane. The lens, which is of the same shape as the lenses often used in lighthouses, has no effect on the beam in the horizontal plane, but in the vertical plane tends to focus the light into an approximately parallel beam.

The lamp includes a generally U-shaped xenon flash tube 20, the two arms 22 of which are parallel and terminate in bent portions 24 extending longitudinally of the drum axis. The beacon is completed by opaque top and bottom disc-shaped cover plates 26 and 28. The cover plates can be sealingly joined to the edges of the lens 12 to provide a dust and moisture tight enclosure in any suitable manner, this is only diagrammatically shown on the drawing.

The bottom cover plate 28 provides the support and electrical connections for the flash tube 20. To this end the lamp has two terminal lead wires 30 which pass through two respective connections 32 and the underside of the bottom plate 28, and a further support and earthing wire 34 which surrounds the tube at the base of the U and passes through a connector member 36. The connectors may be of the plug-in type, or may require angular rotation to provide a locking action against vibration.

The U-shaped xenon flash tube is positioned as shown with the plane of the U being a transverse plane of the drum, as seen in Fig. 1, and the tube being symmetrically placed about the centre of the drum lens, as seen in Fig. 2, the centre in this example being precisely coincident with the lens focus.

The light pattern produced by the lamp comprises a beam which is narrow in the vertical direction due to the focussing effect of the lens. However, the pattern is not constant around the horizontal plane as shown by the plot 40 in Fig. 2 which is superimposed on the cross-sectional view with the focus 18 of the lens being the origin of the plot. In those angular regions where the tube is nearest to the lens focus the light beam has greatest intensity, and vice versa.

It is seen that the lamp provides a more intense beam to left and right, as seen in Fig. 2, than in the other directions.

This is particularly advantageous for beacon lamps such as mounted on emergency vehicles for use on motorways where travelling speeds can be high. The lamp is mounted to give a more intense beam in the fore and aft direction so as to enable it to be more readily detected by other drivers.

It is not essential forthe lens focus to be precisely at the drum centre. It could for example be on a circle the radius of which is approximately the distance from the centre of the nearest part of the flash tube.

In the illustrated lamp the maximum effective source height is the internal diameter of the arc tube.

This provides the possibility of high light intensity in a beam of narrow vertical angle.

Claims (1)

1. 2. A light source according to claim 1, in which the drum-shaped lens member is faceted to reduce its thickness.

   3. A light source according to claim 1 or 2, in which the discharge tube is a Xenon flash tube.

   4. A light source according to claim 1,2 or3, in which the discharge tube has electrical connections which pass through one of the cover members.

   5. A light source according to any preceding claim, in which the drum lens and cover members form a weather-tight enclosure.

   6. A light source according to any preceding claim, in which both cover members are opaque.

   7. A light source substantially as herein described with reference to the drawings.

   New claim filed on 31.1.1980.

   Superceded claims: Claim 1.

   New Claim:

   1. A light source comprising a drum-shaped lens member the focus of which is at or near the central region of the drum cross-section, a U-shaped discharge tube within the drum-shaped lens member lying in a transverse plane of the drum and having side arms which are substantially symmetrically positioned about the centre of the drum such that the perpendicular distance from the focus to each side arm is less than the distance from the focus to any other portion of the tube, and top and bottom cover members for the drum member.