WO2006018756A1

WO2006018756A1 - Luminaire for street lighting

Info

Publication number: WO2006018756A1
Application number: PCT/IB2005/052524
Authority: WO
Inventors: Jozef H. C. Hoens; Hendrik Wijbenga
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-08-19
Filing date: 2005-07-27
Publication date: 2006-02-23

Abstract

The luminaire for street lighting in urban areas has a reflector (1) with a plane of symmetry (2) which is perpendicular to a light-emanating window (4). The reflector (1) has a top panel (10) which extends at an acute angle from the light-emanating window (4). Main portions (20,20') of the reflector extend from said window (4) to the top panel (10) and so do auxiliary portions (40,40'), located closer to a central portion (30) of the reflector. The luminaire may be compact but, when installed aside a street, is nevertheless able to light the street in two directions evenly and with a high efficiency.

Description

Luminaire for street lighting

The invention relates to a luminaire for street lighting, comprising: a concave reflector having a plane of symmetry, an optical center in the plane of symmetry and a light-emanating window transverse to the plane of symmetry; a lamp holder for accommodating an electric discharge lamp having an elongate cylindrical light source in the plane of symmetry and along the light-emanating window, the reflector having a profiled surface.

An embodiment of such a luminaire is known from US 4,507,717. In the known luminaire, the reflector is dish-shaped and is built up with facets extending along the light-emanating window and being curved concave transversely. The reflector is accommodated in a housing and the light-emanating window is closed by means of a voluminous tub-shaped hood.

As is customary with luminaires for street lighting in urban areas, the known street lighting luminaire is intended to be mounted on a mast or on a wall front, with the plane of symmetry perpendicular to the longitudinal direction of the street or road to be lit. The luminaire must then throw the generated light sideways from the plane of symmetry so as to evenly light parts of the street or road on the left and right of the luminaire. A relatively small quantity of light is irradiated along the plane of symmetry so as to also light the other side of the street or road directly opposite the luminaire.

The known luminaire is particularly suitable for high-pressure sodium lamps whose discharge vessel, the actual light source, is not centered in the lamp so that, when placed in the luminaire, it is not certain which position the light source will take up.

It is a drawback of the known luminaire that it is voluminous. A voluminous luminaire has a relatively high weight and catches relatively much wind so that the mast or the bracket from which the luminaire is to be suspended must be very heavy. The known luminaire has a relatively low efficiency of 76%.

It is an object of the invention to provide a luminaire of the type described in the opening paragraph, which can be made relatively compact and nevertheless provides street lighting of a relatively high quality. According to the invention, this object is achieved by the street lighting luminaire defined in claim 1.

When using the luminaire for street lighting, it is arranged on the side of a street, with the light-emanating window being directed substantially horizontally and downwards. The plane of symmetry is perpendicular to the longitudinal direction of the street. The screen points obliquely downwards and is directed towards the opposite side of the street.

The main portions throw light generated by an accommodated lamp far away through the plane of symmetry, obliquely from the luminaire. The plane facets ensure that the incident light is spread. Since the light source has an elongated shape, light rays from the lamp are incident on a facet at various angles so that they are also reflected in various directions and the light is thus spread. The light distribution diagram of the luminaire therefore has two extreme maxima of substantially equal value.

The auxiliary portions also produce a spread reflection through the plane of symmetry obliquely from the luminaire, but towards more proximate parts of the street.

Together with the light emanating from the luminaire without any previous reflection, the top panel lights the street directly underneath the luminaire and the area closely surrounding it. The downward direction of the top panel is important to reflect the incident light downwards to the road surface. This downward direction also prevents the occurrence of double reflections. There is absorption at each reflection, no matter how reflective the material is, so that additional reflections, likewise as with double reflections, cause extra losses.

The central portion completes the concave reflector and is preferably dimensioned to be so small that constructive parts of the lamp, such as the lamp base, the sealing of the lamp vessel in which a gas discharge generating light takes place during operation, and the sealing of an external envelope of the lamp vessel obstruct a direct irradiation of the central portion and throw shadows across this portion. Consequently, the shape of the central portion is of little significance.

A luminaire according to the invention has a construction allowing a compact design.

It is a significant advantage of the luminaire according to the invention that it has a relatively high efficiency. It is another advantage that the lighting efficiency and quality are not very sensitive to a deviation of the position of the light source from its planned position. The street lighting quality manifests a relatively large uniformity and the great extent to which dazzling is prevented.

It is to be noted that a luminaire for lighting motorways is known from WO-A- 03/093723, which luminaire also has a top panel enclosing an acute angle with the light- emanating window. However, this luminaire has a completely different structure and, consequently, completely different properties and a different purpose of use. The known luminaire is placed on the side of a motorway and is intended to light one half of the motorway for traffic in one direction against the traffic driving direction. In this case, the top panel points to the oncoming traffic. To this end, the reflector is asymmetrical and thus misses a plane of symmetry, and the lamp is placed transversely to the optical main surface. The reflector is constructed to radiate the generated light substantially in one direction in a concentrated beam so that the light distribution diagram substantially has one maximum.

For an optimal light distribution, it is advantageous when the facets of each main portion are tangent to their own paraboloid with a focus and an apex on an axis, the focus coinciding with the optical center.

It is also favorable when the axis of each paraboloid encloses an acute angle α with the light-emanating window and an acute angle β with the plane of symmetry, the apex being situated proximate to the relevant main portion. Angle α, which generally ranges between 20° and 30°, is useful for radiating the reflected light more downwards, while angle β, which generally ranges between 72° and 82°, is useful for turning the light further away from the side of the street where the luminaire is installed.

The reflector may be made of a reflective or semi-reflective material, for example, metal. However, it is favorable when the reflector is provided with a lacquer coating having a mirror reflection component. The reflector then reflects the light both in a reflective and a scattering way, which contributes to the homogeneity of the lighting and counteracts stepped brightness transitions.

To obtain high light beam maxima, it is, however, useful when the main portions, remote from the light-emanating window, have facets with a reflective metallic surface proximate to the relevant auxiliary portions. Parts of the street which are relatively far remote from the luminaire then still receive a relatively high brightness. The reflector of this embodiment can be obtained by starting from a reflector having a reflective metallic surface and by shielding the relevant parts of the main portions when applying the coating, or by locally removing the coating. However, it is attractive to give the relevant parts a metal plate cladding. The body can then be made of an inexpensive material which can easily be processed, for example, metal or aluminum without any optical quality. It is useful that the facets bounding on the light-emanating window remain unclad in order to prevent a passer-by who is coming within the area of reflection of these facets from suddenly observing the high luminance of the light source due to the reflection in these facets. The auxiliary portions have their own shape due to their function which deviates from the function of the main portions. This involves a transition of the juxtaposed portions. It is favorable when the reflector has a stepped transition from the main portions to the relevant auxiliary portions, which transition is situated in a plane through the optical center and substantially perpendicularly to the light-emanating window. Transition effects on the light beam formed are thereby effectively counteracted and limited.

It is favorable for the formed light beam when the auxiliary portions have facets which are directed as tangent planes to a respective paraboloid with a focus substantially coinciding with the optical center.

The luminaire according to the invention is suitable for accommodating a lamp chosen from several types and several power values, for example, high-pressure sodium discharge lamps of 70, 150 and 250 W and metal halide discharge lamps of 60, 140, 150 and 250 W, and various dimensions, notably light source lengths of, for example, 21, 30 and 60 mm. To make the center of the light source coincide with the optical center of the reflector, it is favorable when the lamp holder is mounted on a bracket supported by the central portion. By replacing the bracket by a bracket having a different length, a specimen of the luminaire according to the invention can be made suitable for accommodating a lamp of a different length in the optical center.

Said lamps are commercially available with an elongate cylindrical discharge vessel of a ceramic material, for example, aluminum oxide which is accurately positioned with respect to the lamp base and, consequently, accurately positioned by the lamp holder with respect to the reflector. During operation, an electric discharge in a gas mixture, at which light is generated, takes place between opposite electrodes in the discharge vessel. Since the discharge vessel is translucent but not transparent, the dimensions of the light source optically correspond to the distance between the electrodes and the outer diameter of the discharge vessel.

For the compact size of the luminaire, but also for avoiding scattered radiation due to contamination, it is favorable when the light-emanating window is closed by means of a flat transparent plate rather than by a hood. Closing of the light-emanating window is generally desirable to avoid contamination of the reflector and hence loss of reflective power. It is favorable when the reflector is accommodated in a housing which, in a side elevation, is substantially triangular. A space accommodating, for example, an electronic circuit for starting and operating the lamp may then be present on the side of the central portion. Even with a closure plate, the luminaire according to the invention has a relatively high efficiency of more than 80%, also because the occurrence of double reflections is prevented to a great extent.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 is a plan view of the reflector;

Fig. 2 is a longitudinal section of the reflector taken on the line H-II in Fig. 1 in a housing;

Fig. 3 is a front view of the reflector taken on the line III in Fig. 1 ; Figs. 4, 5 and 6 are light distribution diagrams of the embodiments shown in Figs. 1 to 3.

Fig. 1 shows an accommodated lamp, a lamp holder and a bracket, in which the top panel and the central portion are considered to be transparent from the exterior. The other shapes of the reflector are visible on the outer side because the shapes of the inner surface can be distinguished on the outer side. In Fig. 3, the top panel and parts of the main portions are considered to be transparent from the exterior.

In Figs. 1, 2 and 3, the luminaire for street lighting is provided with a concave reflector 1 having a plane of symmetry 2, an optical center 3 in the plane of symmetry and a light-emanating window 4, i.e. the outer contour in Fig. 1, transverse to the plane of symmetry 2. A lamp holder 5 is present for accommodating an electric discharge lamp L_D with an elongate cylindrical light source in the plane of symmetry 2 and along the light- emanating window 4. The reflector 1 has a profiled surface.

The reflector 1 , sec Fig. 2, has a top panel 10 which extends at an acute angle of, for example, between 25° and 35° from the light-emanating window 4. Near its highest point, the panel 10 is kinked so as to have a portion parallel to the light-emanating window 4. The reflector 1, see Figs. 1 and 3, has respective main portions 20, 20' on each side of the plane of symmetry 2 extending from the light-emanating window 4 to the top panel 10 and, as a profiled surface, has substantially plane facets 21, 22, 23 arranged in rows along and in columns on the light-emanating window 4. Furthermore, the reflector 1 has a central portion 30 transverse to the plane of symmetry 2 which extends from the light-emanating window 4 to the top panel 10, while a lamp holder 5 is arranged proximate to this central portion 30. The reflector also has respective auxiliary portions 40, 40' on each side of the plane of symmetry 2, between the relevant main portions 20, 20' and the central portion 30 which extends from the light-emanating window 4 to the top panel 10 and has substantially plane facets 41.

The facets 21, 22, 23 of each main portion 20, 20' are tangent to their own paraboloid in the Figures, with a focus 24 and an apex 25 on an axis 26, the focus 24 coinciding with the optical center 3. The axis 26 of each paraboloid encloses an acute angle α, of 25° in Fig. 3, with the light-emanating window 4, and an acute angle β, of 77° in Fig. 1, with the plane of symmetry 2, the apex 25 being situated proximate to the relevant main portion 20, 20'. In Figs. 1 and 3, the axis 26 is shown for the main portion 20.

Fig. 1 shows that the light-emanating window 4 is tapered at the area where the top panel 10 touches the light-emanating window 4.

The reflector is provided with a lacquer coating having a mirror reflection component. The coating comprises 75% by volume of a translucent silicon binder and 25% by volume of light-reflective particles of titanium dioxide with an aluminum oxide film. Titanium dioxide and aluminum oxide have different refractive indices of 2.32 and 1.63, respectively, so that the mirror reflection by the lacquer is strongly increased.

Remote from the light-emanating window 4 and proximate to the relevant auxiliary portions 40, 40', the main portions 20, 20' have facets 22 with a reflective metallic surface. The facets 22 have an aluminum cladding on the lacquer coating. It is to be noted that Fig. 3 shows that facets 21 of the main portions 20, 20' tangent to the light-emanating window 4 are perpendicular to this window 4 in the embodiment shown, so that they are not visible in Fig. 1.

The reflector 1 has a stepped transition 42 from the main portions 20, 20' to the relevant auxiliary portions 40, 40', which transition 42 is situated in a plane through the optical center 3 and substantially perpendicularly to the light-emanating window 4. The auxiliary portions 40, 40' have facets 41 which are directed as tangent planes to a respective paraboloid with a focus 43 substantially coinciding with the optical center 3. In the embodiment shown, the facets 41 of the column of facets bounding the transition 42 have the position of tangent planes to the paraboloid but are displaced outwardly. A second transition 42' in another plane through the optical center 3 and substantially perpendicular to the light-emanating window 4 separates them from a second column of facets which are tangent planes. As a result of the outward displacement, there are stepped transitions between the facets 41 of said column of facets. Each transition is situated in a plane through the optical center and perpendicularly to the plane of the transition 42. The lamp holder 5 is mounted on a bracket 6 supported by the central portion

30.

The light-emanating window 4 is closed by means of a flat transparent plate 7 of, for example, glass.

The reflector 1 is accommodated in a housing 8 which, in a side elevation, is substantially triangular. The housing has a space in which an apparatus 9 for starting and operating the electric lamp L_D is arranged.

The luminaire shown has an efficiency of 86.3%.

In the luminaire shown in Figs. 1 to 3, a metal halide high-pressure discharge lamp of 140 W with an efficiency of 120 lm/W was accommodated. The light source had a diameter of 7.7 mm and a length of 30 mm. The light distribution of the light beam generated by the luminaire was measured, with the light-emanating window being directed horizontally and downwards.

Fig. 4 shows the light distribution diagram of the light on the surface of a cone having half an apex angle of 80°, the apex in the central position of the lamp and the axis in the vertical position. In the diagram, the vertical axis, 90°-270°, lies in the plane of symmetry 2 of the luminaire, the horizontal axis, O⁰- 180°, is parallel to the longitudinal direction of a street to be lit. The Figure shows that the intensity in the surface of the cone is smaller than 20 cd/klm throughout. The luminaire thus meets the requirement that the intensity in this surface of the cone should nowhere be more than 30 cd/klm or more in order to prevent dazzling.

In Fig. 5, the broken line a shows the light distribution in the plane of symmetry 2 of the luminaire, in which the lamp holder 5 is situated proximate to the origin of the system of coordinates, and the accommodated lamp points to the right. The luminaire radiates more light to the right, towards the street on the side of which the luminaire can be installed, than to the left.

The solid line b shows the light distribution in the vertical plane perpendicular to the plane of symmetry and through the optical center 3 of the luminaire. The luminaire has two maxima of substantially equal value.

In Fig. 6, the lamp holder 5 is arranged behind the origin of the system of coordinates, and the lamp points forwards. The vertical axis, O⁰- 180°, is vertical and lies in the plane of symmetry 2. Both the curve to the left and the curve to the right in the Figure show the light distribution in a plane extending at an angle of 77.5° to the plane of symmetry 2. The planes thus jointly enclose an angle of 155°. These planes are important because they indicate that much light is irradiated in those planes which are directed towards the center of parts of the street that are relatively far remote from the luminaire.

The diagrams show that the luminaire according to the invention is suitable for evenly lighting the street both to the left and to the right when the luminaire is placed on the side of this street. In addition, measurements have proved that lighting with a high efficiency is possible, even when using a compact luminaire.

Claims

CLAIMS:

1. A luminaire for street lighting, comprising: a concave reflector (1) having a plane of symmetry (2), an optical center (3) in the plane of symmetry and a light-emanating window (4) transverse to the plane of symmetry

(2); - a lamp holder (5) for accommodating an electric discharge lamp having an elongate cylindrical light source in the plane of symmetry (2) and along the light-emanating window (4), the reflector (1) having a profiled surface, characterized in that the reflector (1) comprises: a top panel (10) extending at an acute angle from the light-emanating window (4); respective main portions (20, 20') on each side of the plane of symmetry (2), extending from the light-emanating window (4) to the top panel (10) and having a profiled surface in the form of substantially plane facets (21, 22, 23) arranged in rows along and in columns on the light-emanating window (4); - a central portion (30) transverse to the plane of symmetry (2), extending from the light-emanating window (4) to the top panel (10), the lamp holder (5) being arranged proximate to said central portion (30); and respective auxiliary portions (40, 40') on each side of the plane of symmetry (2), between the relevant main portions (20, 20') and the central portion (30), extending from the light-emanating window (4) to the top panel (10) and having substantially plane facets (41).

2. A luminaire as claimed in claim 1, characterized in that the facets (21, 22, 23) of each main portion (20, 20') are tangent to their own paraboloid with a focus (24) and an apex (25) on an axis (26), the focus (24) coinciding with the optical center (3).

3. A luminaire as claimed in claim 2, characterized in that the axis (26) of each paraboloid encloses an acute angle α with the light-emanating window (4) and an acute angle β with the plane of symmetry (2), the apex (25) being situated proximate to the relevant main portion (20, 20').

4. A luminaire as claimed in claim 1 or 2, characterized in that the reflector (1) is provided with a lacquer coating having a mirror reflection component.

5. A luminaire as claimed in claim 4, characterized in that the main portions (20, 20'), remote from the light-emanating window (4), have facets (22) with a reflective metallic surface proximate to the relevant auxiliary portions (40, 40').

6. A luminaire as claimed in claim 4, characterized in that the reflector (1) has a stepped transition (42) from the main portions (20, 20') to the relevant auxiliary portions (40, 40'), which transition (42) is situated in a plane through the optical center (3) and substantially perpendicularly to the light-emanating window (4).

7. A luminaire as claimed in claim 4, characterized in that the auxiliary portions (40, 40') have facets (41) which are directed as tangent planes to a respective paraboloid with a focus (43) substantially coinciding with the optical center.

8. A luminaire as claimed in claim 1 or 2, characterized in that the lamp holder

(5) is mounted on a bracket (6) supported by the central portion (30).

9. A luminaire as claimed in any one of claims 1 to 8, characterized in that the light-emanating window (4) is closed by means of a flat transparent plate (7).

10. A luminaire as claimed in claim 9, characterized in that the reflector (1) is accommodated in a housing (8) which, in a side elevation, is substantially triangular.