GB2079433A

GB2079433A - Marker light suitable for airport runways

Info

Publication number: GB2079433A
Application number: GB8115640A
Authority: GB
Original assignee: Toshiba Electric Equipment Corp
Current assignee: Toshiba Electric Equipment Corp
Priority date: 1980-06-04
Filing date: 1981-05-21
Publication date: 1982-01-20
Also published as: JPS57684A; JPH0121561B2; BE889007A

Abstract

A light source 14 is disposed within a housing 10 having windows 12 therein, and an interference filter 16 is disposed between the source 14 and each window 12 to colour the light emitted through the latter. In order to prevent the chromaticity of the emitted light varying beyond permitted limits due to variations in the angle of incidence upon the filter, each filter 16 is curved so that it presents a concave surface to the light source 14 and the angle of incidence is restricted to 30 DEG or less. <IMAGE>

Description

SPECIFICATION Marker light This invention relates to a marker light for projecting coloured light by means of a coloured filter.

Marker lights of various types are installed in runways of airports and project coloured light. Some of these marker lights use coloured filters for projecting the coloured light, interference filters being presently used for this purpose. Typically, an interference filter is formed by coating a transparent base material with a plurality of interference layers having different refractive indices, using materials such as ZnS, MgF2, etc. A beam passing through such a filter is tinged with a desired colour by means of a variety of interferences caused by various combinations of the interference layers.

Although multilayer coated interference filters are advantageous over coloured glass in having a higher light transmission factor, they are nevertheless subject to the defect that the chromaticity of the transmitted light varies in dependence upon the angle of incidence of the light. Therefore, the chromaticity of the light will vary according to the angle from which the transmitted light is viewed.

The permissible change in the chromaticity of light beams emitted from marker lights is governed by ICAO (International Civil Aviation Organization) Annex-i 4. Among the permissible changes in the chromaticity of various colours provided by ICAO, the one for green is shown in Figure 1 of the accompanying drawings by way of example. In this Figure, crosses represent the chromaticities obtained for beams emitted from a light source with a colour temperature of 2,856"K at various angles 6 of incidence upon a green interference filter. It will be seen that the chromaticities obtained for beams incident at angles ranging from 0" to 30 fall within the permissible range provided by ICAO.On the other hand, the chromaticities obtained for beams incident at angles given by 0 > 30 are not included within the aforesaid permissible range. Accordingly, the angle of incidence 6 of the beam upon a green interference filter must be given by 0 S 30".

In published Japanese patent application no.

129510/80, there is diclosed a marker light which is provided with a reflector and a concave lens for projecting a beam emitted from a light source onto an interference filter at an angle of incidence 0 within a predetermined range. In this marker light, the light source is disposed between the interference filter and the reflector, and the concave lens is located in a position lying on a straight line passing through the light source and the filter and is disposed further from the light source than is the filter.The greater part of the beam emitted from the light source is condensed by the reflector, and is then projected on the filter at 0 < 30 . After passing through the filter, the then coloured beam passes through the concave lens to obtain the characteristics required by lCAO, according to the application of the marker light.

Because a reflector is used, a marker light of such construction involves an increase in the number of components which leads to increased cost and more complicated assembly. Moreover, in marker lights wherein coloured light is projected in a plurality of directions using a single light source, it is impossible to use any reflector at all orto use a good-sized reflector. In the conventional marker light, therefore, it is hard to set within a predetermined angular range the angle of incidence of a part of the beam upon the interference filter. Namely, the chromaticity of the light emitted from the marker light would depart from the permissible range provided by ICAO, depending on the angle from which the coloured light is viewed.If only those beams which are projected on the filter at incidence angles within the predetermined range are used, it becomes necessary to use a light source having a relatively large power consumption, which is contrary to the present-day idea of energy economy.

It is an object of the present invention to provide a marker light which overcomes the problems described above.

According to the present invention, a marker light comprises a housing having a light-projection win dowtherein, a light source disposed in the housing and optically opposed to the light-projection window, and an interference filter opposed to the light source and having a concave surface facing the light source.

The interference filter may be in the form of a curved plate, a plurality of flat plates arranged in a curve, a plate bent only at its ends so as to have a cross-section in the shape of a tray, or may be annular in cross-section.

The invention will now be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a chromaticity diagram showing the permissible change in the chromaticity of a green marker light as provided by ICAO Annex-14; Figure 2 is a plan view of a first embodiment of a marker light according to the present invention; Figure 3 is a sectional view taken along the line 3-3 in Figure 2; Figure 4 is a sectional view taken along line 4-4 in Figure 3; Figure 5 is a perspective view of a modified form of interference filter for use in the marker light shown in Figures 2 to 4; Figure 6 is a sectional view similar to Figure 4 showing a second embodiment of a marker light according to the present invention; and Figure 7 is a sectional view similar to Figure 4, showing a third embodiment of a marker light according to the present invention.

Referring first to Figures 2 to 4, the marker light shown therein comprises a hollow housing 10 having two light-projection windows 12 formed in its top side. A light source 14 (in this embodiment a halogen lamp) is disposed inside the housing 10 and is optically opposed to the two windows 12. Also disposed inside the housing 10 are two interference filters 16 each formed by coating a transparent base material with a plurality of interference layers having different refractive indices, so that the light transmitted therethrough is green. Each filter 16 is in the form of a curved plate and has a concave surface which faces the light source 14.The angle of incidence H of light emitted from the light source 14 upon each filter 16 is given byo S 30 , preferably (3 S 25".

A light-transmitting member 18 is disposed inside the housing 10, and in this embodiment is formed by an annulus of transparent glass material. Those portions 20 of the light-transmitting member 18 which face the light-projection windows 12 are designed to function as lenses, as shown in Figure 4.

After passing through the filters 16, those beams emitted from the light source 14 within respective angular ranges a each corresponding to a horizontal angle of 50 are projected onto the lens portions 20 ofthe light-transmitting member 18, respectively.

The beams after passing through the lens portions 20 are in compliance with the distribution of green light which appears in a table entitled "Light Characteristics for Taxiways intended for use with Runways other than Precision Approach Runways Category Ill" of ICAO Annex-14. That is, these beams are each distributed within a horizontal angular range p = +19.25 .

As described above, the light emitted from the light source 14 is coloured green by passage through the filters 16, after which the light passes through the lens portions 20 of the light-transmitting member 18, and is then projected as a beam into the outside space through the light-projecting windows 12 in the housing 10. The light emitted from the light source 14 is projected onto the filters 16 at an incidence angle 0 given by 0 ";300. Accordingly, the light after passing through the filters 16, if viewed from every direction, can comply with the chromaticity range for green light required by ICAO, as shown in Figure 1.

Because a reflector is not used, the marker light of the present invention is simpler in construction and easierto manufacture and assemble as compared with the conventional marker light described previously. For this reason, the marker light of the invention may be used effectively to emit coloured light in a plurality of directions.

As is evident from the detailed description above, therefore, the marker light of the invention is so designed that the chromaticity of the coloured light which it emits falls within the permissible range provided by ICAO even though the visual angle to the coloured light may change. In addition, the chromaticity requirements of ICAO may be satisfied with use of a light source which requires less power consumption than does the light source used in the conventional marker light.

In the embodiment of Figures 2 to 4, the interference filters 16 are each in the form of a curved plate.

Other forms of filter can however be used within the scope of the invention. For example, each interference filter may be formed from a plurality of flat plates or pieces arranged or connected in a curve, as shown in Figure 5. Alternatively, as shown in Figure 6, each interference filter may be in the form of a plate bent only at its end portions so as to have a cross-section in the shape of a tray. As a further alternative, an interference filter of annular crosssection may be provided, as indicated in Figure 7. It is expressly advisable to use a filter of this latter type with a marker light which emits coloured light in a plurality of directions, as shown.

In the above description, reference has been made to interference filters which colour light passing therethrough green. Itwill of course be appreciated that the invention is applicable to colours other than green, such as red, yellow, orange and blue for example.

Claims

1. A marker light comprising a housing having a light-projection window therein, a light source disposed in the housing and optically opposed to the light-projection window, and an interference filter opposed to the light source and having a concave surface facing the light source.

2. A marker light as claimed in Claim 1,wherein the interference filter is in the form of a curved plate.

3. A marker light as claimed in Claim 1, wherein the interference filter is in the form of a plurality of flat plates arranged in a curve.

4. A marker light as claimed in Claim 1, wherein the interference filter is in the form of a plate bent only at its ends so as to have a cross-section in the shape of a tray.

5. A marker light as claimed in Claim 1, wherein the interference filter is annular in cross-section.

6. A marker light as claimed in any preceding Claim, wherein the angle of incidence of light emitted by the light source on said concave surface of the interference filter is nowhere greater than 30".

7. A marker light as claimed in any preceding Claim, wherein the interference filter is provided with multiple interference coatings.

8. A marker light substantially as hereinbefore described with reference to Figures 2 to 4, or Figures 2 to 4 as modified by Figure 5, or Figure 6 or Figure 7 of the accompanying drawings.