WO2006109258A1

WO2006109258A1 - Luminaire and inspection lighting apparatus

Info

Publication number: WO2006109258A1
Application number: PCT/IB2006/051124
Authority: WO
Inventors: Paulus G. H. Kosters
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-04-14
Filing date: 2006-04-12
Publication date: 2006-10-19
Also published as: MX2007012533A; BRPI0609759A2; TW200702655A

Abstract

The invention relates to a luminaire comprising a housing (2) with a light emission window (3) , the housing comprising an elongated reflector element (4) which is concave towards the light emission window and defines a longitudinal axis. A light distribution element (7) is positioned in such a way that, during operation of the lamp, essentially all light originating from the electric lamp traverses a light distribution element before exiting the housing via the light emission window. The light distribution element is provided with alternating bright (8a, 8b, 8c) and dark bands (9a, 9b, 9c) extending along the axis and yielding areas of a relatively high and a relatively low luminance, respectively. The dark bands are diffusely transparent to light.

Description

Luminaire and inspection lighting apparatus

The invention relates to a luminaire comprising a housing with a light emission window, the housing comprising: an elongated reflector element which is concave towards the light emission window and defines a longitudinal axis; contact means for accommodating an electric lamp and being positioned between the reflector part and the light emission window; a light distribution element being positioned in such a way that, during operation of the lamp, essentially all light originating from the lamp traverses the light distribution element before exiting the housing via the light emission window, the light distribution element being provided with alternating bright and dark bands extending along the axis.

The invention further relates to an inspection lighting apparatus.

Such a luminaire is known from the Internet site http;//www.paramountU^ The known luminaire is suitable for a surface inspection lighting apparatus for use in visual inspections by a human inspector of reflective test surfaces for surface defects, having a region from which light emanates when the apparatus is in use. The alternating bright and dark bands then yield bright areas of a relatively high luminance and relatively dark areas of a relatively low luminance, respectively. The luminance level of the light emanating from said region varies substantially across said region, so that the specular reflection of light from said region in a flat, defect-free, reflective test surface is perceived by a human inspector as having said varying luminance distribution. The inspector looks at the specular reflection of the apparatus in the test surface. If the test surface is reflective, smooth and free of defects, it acts as a mirror and the inspector perceives a steep luminance distribution and can judge that the surface has a good quality.

A surface defect on a reflective surface typically distorts its smoothness. Light specularly reflected by the defect is therefore reflected in a direction different from that of the light reflected by the good-quality surface that surrounds it. When the inspector views the reflection of the apparatus in the test surface, he sees, at the location of the defect, light reflected from a position on the apparatus that is remote from the positions on the apparatus from which light is reflected to the inspector by the good-quality surface surrounding the defect. As the luminance of the light emanating from the apparatus varies across it, the defect is perceived as having a luminance which is different from that of its surrounding area. If the severity and size of the defect are sufficient, the inspector sees a remarkable distortion in the luminance level at the location of the defect, which distortion can be distinguished from the changes in the luminance level due to the spatial pattern of the apparatus.

The reasons for suitability of the luminance distribution are as follows:

First, it is essential that the luminance varies across the apparatus for defects to be visible, as described above.

Secondly, the human visual/perceptual system is sensitive both to step changes in the luminance level within a field of view, and to step changes in a luminance gradient. A person therefore easily perceives visual features of this kind.

Thirdly, research has shown that the luminance level of light perceived by a human is substantially a logarithmic function of the actual luminance. For example, a person judges a small change in a low luminance to be of a similar magnitude as a large change in a high luminance.

A light distribution which approximates the distribution described above can be produced by one or more light sources covered with a light distribution element in accordance with the known luminaire. The light emanating from the light distribution element is made by masking it with a generated pattern.

In the known luminaire, the luminance distribution pattern is in the form of linear, parallel, alternating dark and bright bands. The known luminaire has the disadvantage that it yields dark areas having a substantially zero luminance level.

It is an object of the invention to counteract the disadvantage of the known luminaire. To this end, the luminaire of the type described in the opening paragraph is characterized in that the dark bands are diffusely transparent to light. During operation of the lamp, the dark areas in between the bright areas are thus given a sufficient luminance to enable the inspector, spotting a defect, to follow the defect spot through said dark area and to subsequently mark it, thus being less liable to the risk of losing a once spotted defect when it crosses a dark area. Furthermore, by having given the dark areas a sufficient luminance level, the distorting effect of surrounding/ambient light on the balanced light distribution pattern as yielded by the luminaire of the invention is decreased. The risk of erroneously spotting a defect or missing a defect is thus decreased.

The spatial pattern of light intensity can take a number of forms. The pattern is preferably in the form of linear, parallel, alternating dark and bright bands. Alternatively, the distribution may be a pattern of tiled, or tessellated, polygons such as triangles, squares or hexagons. It appeared that good operation/inspection conditions are attained when adjacent bright bands have a mutual spacing in the range from 10 cm, to counteract mutual distortion, to 40 cm, to prevent that the inspector has to change his position so as to enable him to adequately carry out the inspection.

In an embodiment of the invention, the luminaire is further characterized in that the number of bright bands is three and the number of dark bands is two. In practice, the detection and marking of defects often occurs in three stages. In the first stage, when the defect passes the first bright area, the inspector often notices from the corner of his eyes that a section has a defect. When the inspector directs his attention to the spotted section of the defect, said section passes the second bright area, during which the inspector is able to determine the exact location of the defect. When, finally, the defect passes the third bright area, the inspector is able to mark the defect at its exact location. For pleasant and/or efficient working/inspection conditions, it is preferred that the bright areas have a maximum luminance level which is at least three times the maximum luminance level of the dark areas.

In another embodiment of the invention, the luminaire is characterized in that the dark bands have a width W_d in the range of at least 5*Dt <= W_d <= 20*D_l5 wherein D₁ is the diameter of the electric lamp. The luminaire will often accommodate a fluorescent lamp having a diameter of about 2 cm. It appeared that good operation/inspection conditions are attained when adjacent bright bands have a mutual spacing of at least 10 cm, i.e. 5* D₁, to counteract mutual distortion. However, for good operation/inspection conditions, the bright bands may have a mutual spacing of at most 40 cm, i.e. 20* D₁, to prevent that the inspector has to change his position so as to enable him to adequately carry out the inspection.

In yet another embodiment of the invention, the luminaire is characterized in that the bright band being centrally positioned has a width W_b0 which is approximately equal to the diameter of the lamp, i.e. W_b0 is in the range of 0.9*Di <= W_b0 <= 1.5*Di, wherein D₁ is the diameter of the electric lamp. The central bright band must be large enough to allow viewing a substantially complete image of the (reflected) lamp, i.e. more than 90% of the lamp. In dependence upon the shortest distance between the lamp and the reflector, preferably a distance which is approximately equal to the lamp diameter, this means that the lamp can be enlarged via the reflector by a factor of at most about 1.5 in the luminaire of the invention.

In still another embodiment of the invention, the luminaire is characterized in that the bright bands being positioned at outer sides of the light distribution element have a width W_bo in the range of 2*Dt <= W_b0 <= 8*Di, wherein D₁ is the diameter of the electric lamp. The width W_b0 depends, inter alia, on the shape of the reflector and its reflective properties, i.e. being specular or partly specular. Practical experience revealed that very good operation conditions are attained for the given range of W_b0.

In a further embodiment, the luminaire is characterized in that the reflector element has a central, diffusely reflective part and two, specularly reflective side parts which are mirror-positioned/symmetrically positioned with respect to the lamp and to said diffusely reflective part. The desired light distribution pattern, i.e. alternating areas with a high and a low luminance, respectively, is then easily obtained by a single electric lamp instead of a plurality of lamps accommodated in the luminaire. A relatively inexpensive inspection luminaire of a relatively good quality is thus obtained. The diffusely reflective part yields a relatively low luminance level of the dark areas, and the specularly reflective side parts yield reflection images of the electric lamp with a high luminance of the bright areas. The specularly reflective side parts are preferably positioned at an acute angle α to the light emission window, α being in the range of 35° <= α <= 55°, so that the dimensions of the luminaire do not become too large in directions transverse to the axis and/or transverse to the light emission window. For a high efficiency of the luminaire, the central diffusely reflective part is provided with a white coating.

In another embodiment, the luminaire is characterized in that, directly opposite the electric lamp, the reflector part is provided with an axially extending, elongated reflective ridge which protrudes in the direction of the electric lamp. It is thus counteracted that numerous reflection images are observed due to the mirror-positioned/symmetrically positioned specularly reflective side parts. To counteract loss of light and distortion of the light distribution pattern by said ridge, the reflective ridge has a specularly reflective front facing the electric lamp, the front having a width V_r in the range of 0.5*D! <= V_r <= 2*D_ls wherein D₁ is the diameter of the electric lamp.

In a further embodiment, the luminaire is characterized in that it is provided with a screening ridge at each dark band of the light distribution element, each screening ridge extending, across a distance which is approximately equal to the lamp diameter, substantially perpendicularly from the light distribution element towards the diffuse reflector part. It is thus counteracted that multiple images of the lamp are observed after multiple reflection in the two specularly reflective side parts. Said screening ridges may be provided at edges of the dark bands bordering the bright bands which are positioned at the outer sides of the light distribution element. However, said screening ridges are preferably provided at edges of the dark bands bordering the central bright band.

The luminaire and its various embodiments according to the invention as described in the preceding paragraphs can be used very favorably in an inspection lighting apparatus for visual inspection of painted bodies for paint defects and other shortcomings, for example, for car bodies or pieces of furniture. In these applications, a number of units of the luminaires may be configured as a planar array. A vertical array may form a wall, while a generally horizontal array may form a ceiling. On a car body paint inspection line, it is preferred to use two wall arrays to provide coverage of the entire vehicle. These walls are typically placed in positions facing each other, on opposite sides of the vehicle body under inspection. Where this provides insufficient coverage, a generally horizontal ceiling array may be added to form an arch, or positioned separately as a stand-alone array. Depending on the application, the arrays can also be configured as a wall on its own, or as a single wall in conjunction with a ceiling array. A ceiling array alone could be employed where inspection is intended for generally horizontal surfaces only.

The invention will be elucidated by means of the schematic drawings in which,

Fig. 1 is a cross-section of a first embodiment of the luminaire transverse to the axis;

Fig. 2 shows a detail of a cross-section of a second embodiment of the luminaire transverse to the axis;

Fig. 3 is a luminance graph of the light distribution of the luminaire of Fig. 2.

Fig. 1 is a cross-section of a first embodiment of a luminaire 1 transverse to a longitudinal axis 11. The luminaire 1 has a housing 2 with a light emission window 3. The housing comprises an electric lamp 10, a fluorescent lamp in the Figure, but this may be alternatively an elongated halogen lamp or an array of LEDs, accommodated in contact means (not shown) and positioned between the light emission window 3 and a reflector element 4 having a central, diffusively reflective reflector part 5 provided with white, diffusely reflective material, and having two, specularly reflective side parts 6a, 6b extending at an acute angle α of about 45° to the light emission window 3. A light distribution element 7 is positioned substantially in the light emission window 3, such that, during operation of the lamp 10, substantially all light originating from the lamp 10 passes through said light distribution element 7. The light distribution element 7 has five bands, i.e. alternating bright bands 8a, 8b, 8c and dark bands 9a, 9b that extend along the axis 11. The dark bands 9a, 9b are diffusely transparent to light which, during operation of the lamp 10, yields areas that have a luminance which is less than one third of the luminance of bright areas yielded by the bright bands.

Fig. 2 shows a detail of a cross-section of a second embodiment of a luminaire 1 transverse to a longitudinal axis 11. The luminaire 1 has a housing 2 with a light emission window 3. The housing comprises an electric lamp 10 accommodated in contact means (not shown) and positioned between the light emission window 3 and a reflector element 4 having a central, reflector part 5 and two specularly reflective side parts 6a (not shown), 6b. The reflector part 5 is provided with an axially extending, elongated ridge 12 having a front 13 facing the lamp. The ridge has a height H_r of about one time the lamp diameter D₁ and the front 13 has a width V_r of about one time the lamp diameter D₁. A light distribution element 7 is positioned substantially in the light emission window 3, such that, during operation of the lamp 10, substantially all light originating from the lamp 10 passes through said light distribution element 7. The light distribution element 7 has five bands, i.e. alternating bright bands 8a (not shown), 8b, 8c, i.e. one central bright band 8c and two outer bright bands 8a, 8b, and dark bands 9a, 9b that extend along the axis 11. The dark bands 9a, 9b have a width W_d of about six times the lamp diameter D₁, the central bright band 8c has a width W_b0 of about one time the lamp diameter D₁, and the outer bright bands 8a (not shown), 8b have a width W_bo of about five times the lamp diameter D₁.

Fig. 3 shows a graph of the luminance observed by an inspector viewing in a direction substantially perpendicular to the light emission window of the luminaire of the invention. The graph clearly shows the steep luminance slope between the bright areas 18a, 18b, 18c yielded by the bright bands and the dark areas 19a, 19b yielded by the dark bands. The maximum luminance level of the bright areas 18a, 18b, 18c is about eight times higher than the maximum luminance level of the dark areas 19a, 19b. The luminance level of the dark areas 19a, 19b is substantially higher than zero.

Claims

CLAIMS:

1. A luminaire comprising a housing with a light emission window, the housing comprising: an elongated reflector element which is concave towards the light emission window and defines a longitudinal axis; contact means for accommodating an electric lamp and being positioned between the reflector part and the light emission window; a light distribution element being positioned in such a way that, during operation of the lamp, essentially all light originating from the electric lamp traverses the light distribution element before exiting the housing via the light emission window, the light distribution element being provided with alternating bright and dark bands extending along the axis, characterized in that the dark bands are diffusely transparent to light.

2. A luminaire according to claim 1, characterized in that the number of bright bands is three and the number of dark bands is two.

3. A luminaire according to claim 1 or 2, characterized in that, during operation of the lamp, each band yields an area having a maximum luminance level, the maximum luminance level of the areas yielded by the bright bands being at least three times the maximum luminance level of the areas yielded by the dark bands.

4. A luminaire according to claim 1, 2 or 3, characterized in that the dark bands have a width W_d in the range of at least 5*Dt <= W_d <= 20*D_l5 wherein D₁ is the diameter of the electric lamp.

5. A luminaire according to claim 1, 2 or 3, characterized in that the bright band being centrally positioned has a width W_b0 in the range of 0.9*Di <= W_b0 <= 1.5*Di, wherein D₁ is the diameter of the electric lamp.

6. A luminaire according to claim 1, 2 or 3, characterized in that the bright bands being positioned at outer sides of the light distribution element have a width W_b0 in the range <= W_bo ^<= 8*Di, wherein D₁ is the diameter of the electric lamp.

7. A luminaire according to claim 1, 2 or 3, characterized in that the reflector element has a central, diffusely reflective reflector part, and two, specularly reflective side parts symmetrically positioned with respect to the lamp.

8. A luminaire according to claim 7, characterized in that the specularly reflective parts are positioned at an acute angle α to the light emission window, α being in the range of 35° <= α <= 55°

9. A luminaire according to claim 7 or 8, characterized in that, directly opposite the electric lamp, the reflector part is provided with an axially extending, elongated reflective ridge which protrudes in the direction of the electric lamp.

10. A luminaire according to claim 9, characterized in that the reflective ridge has a specularly reflective front facing the electric lamp, the front having a width V_r in the range of 0.5*D! <= Vr <= 2*D_ls wherein D₁ is the diameter of the electric lamp.

11. A luminaire according to claim 7 or 8, characterized in that it is provided with a screening ridge at each dark band of the light distribution element, each screening ridge extending, across a distance which is approximately equal to the lamp diameter, substantially perpendicularly from the light distribution element towards the diffuse reflector part.

12. An inspection lighting apparatus, characterized in that it comprises at least one luminaire according to any one of the preceding claims.