GB2302938A - An energy saving spotlight - Google Patents

Abstract

Two approaches to reducing the energy requirements for lighting are to use an energy-efficient method of light generation and to use some form of optical system to concentrate the light. Both are achieved by using a compact fluorescent energy-saving bulb mounted in a reflector. The reflector required is larger than traditionally used with spotlights but a practical design is possible by using conical reflecting surfaces. A simple method of adjustable mounting may be provided by using a cord and eyelet system.

Description

A LOW ENERGY SPOT LIGHT The invention relates to lighting and in particular to the problem of producing practical forms of energy efficient lighting.

A form of light source which has been widely used for many years is the standard tungsten filament bulb, usually used in combination with some sort of light shade or diffuser. Since the introduction of this, there have been continuing efforts made to find more efficient ways of providing lightning.

One approach has been to develop light sources which are more efficient than the standard tungsten filament light, in terms of the electrical power consumed for a given total light output Various alternative sources have been developed, especially the widely used fluorescent tube. A significant development in recent years has been the low energy light bulb which is a development of the fluorescent tube enabling it to be used as a direct replacement for the standard tungsten filament bulb. To make the system sufficiently compact, one or more fluorescent tubes is folded and assembled into a compact unit and the electronic components required to permit operation of the fluorescent tubes are incorporated within the unit.

An alternative approach to increasing efficiency is to use some sort of optical system, typically a reflector or lens, to direct the light from a source so that it is concentrated in the required area Lighting systems employing this principle are known as spot lights. The use of such spot lights is not only for increased efficiency, however. Often, in living environments for example, it is preferred to have at least some light directed into specific areas to create desired aesthetic lighting effects.

The production of a directed beam of light by the use of a reflector or lens requires, to be effective, that the overall dimension of the reflector or lens is generally larger than that of the source of the light This has meant, for example, that spot lights for domestic use have usually used tungsten filament light sources. It would be much less effective to use a normal fluorescent tube light source for this purpose because of its long length.

It is, however, possible to consider the use of a reflector in combination with a low energy light bulb as a practical means of producing a directed beam of light This would result in a combination of the advantages of both high efficiency of light production and of a directed light beam. Since the low energy light bulb has a size of light source somewhat larger than a typical tungsten filament bulb, however, the size of the reflector has to be correspondingly larger.

Usually, the reflectors that have been used to produce directed beams have been paraboloid in form, or some close approximation to this. This is not strictly necessary however and a feature of the present invention is the use of an alternative form which is more practical to manufacture.

It is normally required that a lighting system producing a directed light beam should have some means of adjustment of the direction of the light beam. This is usually achieved by having a means of adjusting the direction of the unit comprising the combination of the light source and reflector with the electrical connection to the light source being made by a flexible electrical cable. Many arrangements are widely used for providing such a means of adjustment Typically such means involve the use of rotating joints and clamping screws.

These are not always easy to operate and another feature of the present invention is a means of achieving this with greater convenience.

The design and operation of any such adjustable support system will be greatly facilitated if the weight distribution of the reflector, with the light source fitted, is such as to minimise the torque which the adjustment system will have to apply in order to maintain the required pointing direction. This condition can be achieved by making the part of the reflector at the greatest distance from the light source to be as lightweight as possible.

According to the present invention, there is provided a combination of a typical low energy light bulb with a reflector for producing a directed light beam and an adjustable support system for the reflector, the reflector having two distinct joined parts, each part having a reflecting surface which has the form of part of the inner surface of a separate cone, the two parts being of substantially different methods of construction, the upper part being relatively robust and carrying the holder for the light bulb and attachments for the support system and the lower part being of relatively lightweight construction, the support system employing a continuous cord passing through two sets of eyelets, one set on the upper part of the reflector and one set on a fixed support, each set of eyelets being disposed equi-spaced around a circle.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a perspective view; Figure 2 shows a sectional view; Figure 3 illustrates the notional division of the conical reflecting surfaces into trapezoidal sections as required for the purposes of a method of calculation to be described; Figure 3 is a simplified sectional view showing certain drawing constructions required for the purposes of a method of calculation to be described.

Referring to the drawings, the complete system comprises the joined lower part 1 and upper part 2 of the reflector, a support cord 4, an upper fixed support 3, a light bulb 7, shown for the present purposes as an approximate representation of a typical such unit, a flexible electrical cable 5 and a standard bulb holder 6 in which the bulb 7 is mounted. The surfaces 12 and 13 are the conical reflecting surfaces of the reflector. Eyelet 14 is typical of the set which is fixed to the upper support 3 and eyelet 15 is typical of the set fixed to the upper part 2 of the reflector.

The view in figure 1 shows a perspective view of the system in a tilted position.

The method of adjustment is to manually raise the reflector slightly, adjust the amount and direction of tilt to that required, and to release it in this position. In the raised position, the friction generated by the contact of the cord with the eyelets is not sufficient to prevent the cord from sliding through the eyelets to take up the new position but once the system is released, and the cord is under tension, the friction is then sufficient to prevent further movement, provided the torque required to hold the system in position is not excessive.

The number of eyelets shown in each set is 6. Different numbers are possible but 8 or more could lead to difficulty in achieving the adjustment due to friction in the eyelets and less than 3 would not be sufficient to define the pointing direction.

The view in figure 2 shows a section through the axis of symmetry of the reflector with the tilting adjustment set so that this axis of symmetry is vertical.

It illustrates the different methods of construction of the upper and lower parts, the upper part being of relatively thick material and the lower part of relatively thinner materiaL By way of example, the upper part might be made of ceramic material, perhaps in the range 2 to 6 millimetres thick and the lower part by the construction techniques commonly used to make light shades involving the use of stiff fabric or paper and reinforcing wire loops The required reflective surfaces may be created by bonding reflective material such as aluminium foil, supplied in flat sheet form, onto the conical surfaces 12 and 13.

In order to specify the precise geometrical parameters of the reflecting conical surfaces 12 and 13 it is necessary to have a means of estimating the form of the directed beam produced by a given arrangement In order to carry out the estimation, it is first necessary to represent the light source as simplified into a cylindrical form. This is possible with typical low energy bulbs which usually have a group of closely spaced tubes which, for practical purposes, can be approximately represented in this way. A typical 23 watt bulb has an arrangement of tubes which roughly fill a cylindrical volume of about 30mm diameter by 90mm length. In figure 4, item 8 represents a section through such a cylinder, representing just the light emitting source associated with the bulb.

Suppose one now considers each of the conical reflecting surfaces to be approximated by a large number of long thin plane mirror segments, all trapezoidal in form and fitted together to correspond closely to the conical surface. The arrangement of segments is illustrated in figure 3 which shows a view looking approximately perpendicularly onto a part of the surface from the inside. Each of these mirrors can be thought of as forming an image according to the simple laws of reflection at a plane mirror. The beam reflected from each segment can be thought of as that which would occur if there was a light source at the image position, the light from which passed through an aperture whose shape was the same as that of the segment.The validity of the approach rests on showing that the outcome of the calculation does not depend on the number of trapezoidal segments selected, provided it is large enough, since the larger this number is made the closer the form approximates to a true conical form.

If one were to look upwards from a given position below the reflector, then if at least some part of the image was visible through each part of a given segment, the whole of the segment would appear to be illuminated as brightly as if one were looking directly at the side of the light source itself, apart form any loss due to the reflection coefficient of the reflecting surface. On the other hand, if any part of the image was only visible through a part of the segment, only this part would appear illuminated.

The principle of the method of calculation is to calculate the total area which appears illuminated, projected onto a plane perpendicular to the viewing direction The illumination intensity at the viewing point is that which would be produced by a light source of the same brightness as the original light source, corrected for any loss due to reflection coefficient, having this calculated projected area.

To carry out this method in full for any arbitrary viewing point would be laborious, but the method can relatively easily be used to establish what parameters of the conical surfaces must be used to obtain the maximum illumination at a point on the axis of symmetry of the system at any given distance. This will be achieved when the visible illuminated area includes the whole of each segment, that is to say, some part of the image must be visible through every part of each segment For a point on the axis of symmetry, it is only necessary to show that this applies for a single segment since all segments are then equivalent in this case.

There are two particular requirements to be met to achieve this full illumination condition. One requirement is that the width of each segment should be sufficiently small that the view through it will not include the edges of the image. Since the size of the image is the same as the original light source, this means that the maximum width of the segment must be substantially less than this. This can always be achieved by specifying that the surface is divided into a sufficiently large number of segments The second requirement is that the view through the segment should also not include the ends of the image. This condition can be assessed by reference to figure 4 which indicates the positions of the images formed in two segments lying at the right hand edge of the view shown.The upper image 9 is that formed by the segment in the upper part 2 of the reflector and the lower image 10 is that formed in the lower part 1 of the reflector.

The problem becomes one of trial and error where one selects different geometrical parameters for the conical reflecting surfaces and assesses the relative positions of the image, the segment and the viewing point 11 to see whether the second of the above requirements is met The lines 14 and 15 in figure 4 marked with arrowheads indicate the extreme viewing directions which do not pass beyond the ends of the images. Since the images overlap, any line between these lines will correspond to a viewing direction in which full illumination of a segment will be seen. It is apparent from this that the geometrical parameters used in the figure are such as lead to most of the reflecting surface being illuminated in this case.

It is readily seen that the second of the above requirements is not affected by the number of elements chosen and that the first requirement is similarly not affected provided the number of elements chosen is high enough. The number of elements chosen can therefore be made as high as desired without affecting the result, this being the required condition for validity of the approximation.

Some idea of the extent over which the area of maximum intensity occurs can be obtained by considering what happens when the viewing point is moved.

Returning to the situation described in figure 4, with a very large number of narrow segments, it can be seen that if the viewing point is moved in or out of the paper the illumination will disappear when the view through the segment is beyond the edge of the image. The amount of movement required for this to occur will depend on the width of the image and hence of the light source and will be equal to this scaled up by a factor dependent on the geometrical factors involved. In the case of sideways movement of the viewing point, much more movement will be involved until the illumination disappears and it will fall off gradually as the view through the segment gradually sees less of the length of the image.

The patch of illumination created by each single segment will therefore be an elongated patch. All such patches from the different segments will combine to create a centrally bright patch whose size depends on the width of the light source with the intensity gradually falling off around this area.

It is possible to use the methods described to evaluate the effects of various geometrical parameters for the conical surfaces other than those which lead to the maximum brightness on axis. Generally, the lower intensity beams will be distributed over wider areas.

Claims (8)

1. A spot light including a compact fluorescent low-energy light bulb, a reflector, and suitable mounting means, the reflector having an inner reflecting area which is substantially specularly reflective, at least two thirds of the area of the inner reflecting area having a substantially conical form or having substantially the form of a combination of two different conical forms 2. A spot light as claimed in Claim 1 in which the reflector has two distinct parts, the first part being of relatively robust construction and carrying a lamp holder and mounting means and the second part being of relatively lightweight construction, being attached to the first part, and providing an inner reflecting area of substantially conical form.

3. A spot light as claimed in Claim 2 in which the first part of the reflector also provides an inner reflecting area in addition to that provided by the second part 4. A spot light as claimed in Claim 3 in which the additional inner reflecting area provided by the first part of the reflector is substantially conical in form.

5. A spot light as claimed in Claim 2 in which the second part of the reflector is manufactured in the manner of a traditional lamp shade including the use of a suitable fabric, paper or plastic material supplied in flat sheet form and metal wire loops 6. A spotlight as claimed in any preceding claim in which the provision of inner reflective areas having a conical form includes the use of reflective material supplied in flat sheet forum.

7. A spot light as claimed in any preceding claim in which the mounting means comprises a continuous or joined loop of cord passing through two sets of eyelets, one set being fixed to the spot light and the other set being finned to a separate part attached to a downward facing surface such as a ceiling in a way which allows the orientation of the spot light to be adjustable.

& A spot light substantially as described herein with reference to figures 1Q of the accompanying drawing Amendments to the claims have been filed as follows CLAIMS 1. A spotlight including a compact fluorescent energy-saving light bulb, a housing and suitable mounting means, one or more regions of the inner surface of the housing being provided with a reflective surface which is substantially specularly reflective, at least two thirds of the total area of reflective surface so provided lying substantially on a surface defining a main conical reflecting area, the surface defining such a main conical reflecting area being the curved surface of a cone lying between two planes perpendicular to the axis of such a cone, the diameters of the circles of intersection of the planes with the surface of the cone being such that the larger is no more than three times the smaller, there being no reflective surface lying substantially on the indefinitely extended curved surface of the cone not lying between the two planes.

2. A spotlight as claimed in Claim 1 in which- thelight-emitting part of the light bulb is arranged substantially co-axially with the main conical reflecting area and in which the axial length of the light-emitting part of the light bulb is not substantially greater than the minimum required to enable the whole of the reflective surface lying substantially on the main conical reflecting area to appear illuminated by the light bulb when viewed from a distant point lying on the common axis of symmetry.

3. A spotlight as claimed in Claim 1 or Claim 2 in which a substantial part of any reflective surface additional to that lying substantially on the main conical reflecting area has a substantially conical form distinct from that of the main conical reflecting area, the distinction between the corresponding conical forms including a significantly different cone angle.

4. A spotlight as claimed in Claim 1, Claim 2 or Claim 3 in which the housing has two distinct parts, the first part being of relatively robust construction and carrying a bulb holder, mounting means, and any reflective surface in addition to that lying substantially on the main conical reflecting area and the second part being of relatively lightweight construction, being attached to the first part, being of a substantially conical form and providing the main conical reflecting area.

5. A spotlight as claimed in Claim 4 in which the second part of the housing is manufactured in the manner of a traditional lamp shade including the use of a suitable fabric, paper or plastic material supplied in flat sheet form and metal wire loops.

6. A spotlight as claimed in any preceding claim in which the provision of a substantially specularly reflective surface includes the use of appropriate reflective material supplied in flat sheet form.

7. A spotlight as claimed in any preceding claim in which the mounting means comprises a continuous or joined loop of cord passing through two sets of eyelets, one set being fixed to the spotlight and the other set being fixed to a separate part attached to a downward facing surface such as a ceiling in a way which allows the orientation of the spotlight to be adjustable.

8. A spotlight substantially as described herein with reference to figures 1-4 of the accompanying drawing