GB2151418A - An illuminator and circuit arrangement therefor - Google Patents

Abstract

An illuminator comprises two gas discharge lamps (1) and a circuit arrangement therefor where the two lamps are arranged in parallel with one another, the first lamp being connected serially only with a capacitor and the second lamp is supplied from the power supply in a serial connection with only a choke-coil. In an embodiment the capacitor may be serially connected with a regulating unit which is also connected across the terminals of the power supply. <IMAGE>

Description

1 GB 2 151 418A 1

SPECIFICATION

An illuminator This invention relates to an illuminator comprising a gas (vapour) discharge lamp, advantageously a shortarc metal-halogenide lamp and light deflecting focussing (burning) mirrors.

According to the invention there is provided an illuminator comprising a gas discharge lamp and a plurality of light deflecting focussing mirrors, in which two such mirrors are arranged on one side of the lamp in such a way that their axes are parallel with the axis of 80 the arc of the lamp, and the arc of the lamp is arranged outside the foci of the mirrors, and two virtual lamp arcs projected by the two mirrors are on the two sides of the arc of the lamp.

Preferably, a third, considerably larger, focussing mirror is arranged facing them on the other side of the lamp, resulting in spreading three adjacent arc-lights instead of one into the space to be illuminated. Thus, three interwoven light maxima of reduced intensity are obtained, resulting in a much more uniform illumination than by previously known methods. The two smaller mirrors shade the lamp outwards eliminating glare. In interior spaces with a height of less than 6m the two focussing mirrors are turned towards the space to be illuminated and the lamp is covered with a light diffuser.

The evenness of the illumination can be considerably improved by integrating two such light sources. This produces two unex pected additional advantages. Firstly, if two such lamps are located quite near one another, then in a new circuit arrangement developed for it a capacitor and a choke-coil can be omitted from among the conventional circuit elements. Secondly, the dark intervals between the alternating flashes of the two lamps are shorter, i.e. the fight modulation is smaller than usual, and reactive power con sumption is also lower.

High pressure gas (metal-halogenide va pour) discharge lamps have been used for more than four decades. In recent years short- 115 arc metal-halogenide lamps with mixed dopes have become more and more widely used, due to their long life, their ideal colour tem perature (which can be adjusted in advance) and their very high efficiency. However, be cause of their very strong glare effect, caused by the intensively brilliant emission of the nearly punctiform light source, they are not suitable for illuminating interior spaces as di rect light sources. Accordingly, they must be 125 arranged inside illuminators provided with covering and light deflecting elements. In some known solutions relating to such a method, wherein the angle of light spreading of the illuminator is less than 90', the cover- 130 ing plate forms a strong minimum in the centre of the light beam, and tiny, but still glaring light maxima are concentrated into certain points of the space by light homogen- izing bosses arranged on the inner surface of the covering element. As a result, such an illuminator is not suitable for uniform illumination. Illuminators provided with a focussing mirror according to Hungarian Patent Specifi- cation No. 173,640 and to German Patent Specification No. 1, 9 19,19 9 are free of this drawback. The first comprises a larger focussing mirror of elliptical shape and a smaller one of hyperbolic shape, while the other comprises a larger mirror of at least partly parabolic shape and a smaller one of elliptical shape, where the focuses of both mirrors are at the same point and inside the metal-halogenide lamp, and in its arc, respectively. The smaller mirror covers the arc of the lamp outwards, so that it has no glaring effect. A light beam of uniform intensity is projected by the larger mirror, but cver a very small angle of spreading. Accordingly, these illuminators are exclusively employed as head-lamp units for vehicles, and their use for interior illumination is out of the question. Moreover, this arrangement involves a very disadvantageous effect, which is that a part of the light and heat beams reflected by the mirrors are focused inside the lamp, as a result of the foci being inside the lamp, resulting easily in thermal overload of the lamp and hence in shortening the life of the lamp.

A very unfavourable effect involved in the operation of short-arc metalhalogenide lamps by alternating current is the very intensive light modulation as the arc-light of the lamp goes out twice per cycle for a considerable proportion of the cycle time. The completely dark intervals in the cycle can be eliminated by a three phase lamp system, but the amplitude of light modulation is still considerable. Indeed metal-halogenide illumination using al- ternating current of a single phase may be unusable in some cases. The invention disclosed in Hungarian Patent Specification No. 173,720 offers a solution for eliminating this unfavourable effect and for making it endurable, respectively, where each lamp according to it comprises two controllable switches, a voltage and a current comparator, an oscillating circuit, an RC-branch, and other components in addition to the conventional ignition lamp, choke-coil and capacitor. However, the operational calibration and adjustment of the components requires considerable skill in electronics and a high degree of instrumentation. Accordingly, such an apparatus can only be used in special circumstances, for example in film or television studios, or, e.g. in a portable version, by reporters, but not for general illumination.

On the basis of all these, a solution facilitating the use of short-arc metal-halogenide 2 GB 2 151 418A 2 lamps also for general illumination, i.e. including illumination of internal spaces, is required, where the illuminator spreads the luminous flux uniformly over a large area and has no glaring effect, and where the degree of light modulation and reactive consumption is low and the additional tooling is simple and contains but a few elements.

This is sought to be achieved according to an embodiment of the invention by an illuminator employing a short-arc metal-halogenide lamp along with three focussing mirrors, or two focussing mirrors and a light diffuser and two such illuminators are arranged one beside the other to further improve light spreading characteristic. This illuminator preferably has an operational circuit arrangement allowing the saving, for a pair of lamps, of a capacitor and a choke-coil, and can operate with con- siderabiy reduced light modulation and reac- tive power consumption.

The invention is further described by way of example, with reference to the accompanying schematic drawings, wherein:

Fig. 1 shows a lamp and two focussing 90 mirrors; Fig. 2 shows the are of the lamp and the two virtual arcs, and also shows the luminous flux produced by them; Fig. 3 shows a three focussing mirror ar- 95 rangement; Fig. 4 shows an arrangement of two focuss ing mirrors and a light diffuser; Fig. 5 shows the light source according to Fig.4 spatially arranged to illustrate the relation between the 100 scales of principal dimensions of the space and the shape of the diffuser; Fig. 6 shows an arrangement of two focussing mirrors located on one side of the lamp along with a mirror interruption eliminating the luminous flux minimum caused by the shading and with small bosses eliminating light glare; Fig. 7 shows an arrangement similar to Fig.

6 but with narrow, embossed ribs instead of 110 small bosses; Fig. 8 shows one type of mirror arrange ment for two integral illuminators; Fig. 9 is a diagram of a conventional opera tional circuit of a lamp; Fig. 10 is a diagram of a circuit arrange ment developed for the operation of the two integral illuminators; Fig. 11 is a graph of the light pulses generated by the one lamp circuit arrange- 120 ment according to Fig. 9 during one period of the mains supply; Fig. 12 is a graph of the light pulses generated by the circuit arrangement accord ing to Fig. 10 during one period of the mains supply; Fig. 13 is a circuit diagram of the two-lamp regulated arrangement; Fig. 14 is a block diagram of the regulating ing to Fig. 13; and Fig. 15 is a graph of the alternately induced light pulses in the two- lamp regulated arrangement according to Fig. 13 during one period of the mains supply.

The basic elements of the light source according to the invention are schematically shown in a cross-sectional side view in Fig. 1. This shows two focussing mirrors 2,3 each having a surface which is an ellipsoid of rotation adjacently arranged on one side of a short-arc metal-halogenide lamp 1. The mirrors are turned towards the space to be illuminated in such a way that their adjacent edges 35 and an axis of each are parallel to the axis of the lamp 1, and the edge 35 lies nearest to the lamp 1. As the lamp 1 is arranged outside the focal points of the two mirrors 2,3 respective virtual lamp images 8,9 are formed by the mirrors. The effect, as shown in Fig. 2, is as if there were three arc-lights 43, 44, 45 and the space to be illuminated receives the resultant light distribution 10 summed from the light distribution 46 of the arc 43, the light distribution 47 of the virtual arc 44 of the virtual lamp image 8, and the light distribution 48 of the virtual arc 45 of the virtual lamp image 9.

The resultant light distribution 10 is clearly wider than the original light distribution 46, as it results from a wide oblong light source instead of the short, line-shaped fight source of the lamp 1. This however, is not suitable for immediate illumination of inner spaces. For this reason, the mirrors 2,3 may be placed under the lamp 1 according to the scheme of Fig. 3 and a larger focussing mirror 4 having a surface which is advantageously an ellipsoid of rotation is placed on the other side of the lamp 1. One end 36 of the mirror 4 partly encircles the lamp 1 and the end 36 is adjacent the external edge 37 of the smaller mirror 2, resulting in a much more even illumination of much bigger spaces by way of the light spread by the larger mirror 4, than by any other method so far.

Instead of using a mirror 4 with an ellipsoidal surface, a mirror with a cylinder jacket-like surface, i.e. the generatrix of which is perpendicular to the bend, can also be employed. Although such a mirror gives less even light spreading it has the great advantage that it can be assembled also from mirror-band pieces, e.g. by sliding them one after the other into two guide-support notches. One consequent advantage is that if the curvature of the guide-support notches can be varied later, then the spreading of luminous flux can be optimally adjusted on site, when the light source is mounted.

If necessary, the covering effect displayed outwards of the two smaller mirrors 2,3 can be eliminated by making two narrow breaks 33,34 into the reflecting surface in the stripe unit shown in the circuit arrangement accord- 130 adjacent the contacting edges 35 of the mir- 3 GB 2 151 418A 3 rors 2,3 under the lamp 1. This is shown in Fig. 6. Tiny bosses can be arranged adjacent to one another on the external surfaces of the transparent bearing materials 6,7 of the mir- rors 2,3 which disperse the direct radiation of 70 the lamp 1 by acting as tiny lenses, and so eliminate glare. These small adjacent bosses 8 can be simply formed so that tiny pyramids with arched sides confined with the penetra- tion lines, eg. as arched arcs of intersecting concave ribs, are formed, i.e. notches are milled beside one another into the tool machining the mirror body by a miller of a semicircular edge, afterwards said notches are cut through in a perpendicular direction in the 80 same depth. Instead of the bosses 8, narrow concave ribs 11, 12 can be provided parallel to the edge 35 as shown in Fig. 7, considering the transparency and refractivity of the transparent bearing materials 6,7.

The two breaks 33,34 are useful because the area illuminated by the threelamp arrangement shown in Fig. 3 is augmented by the area that had. not been illuminated earlier because of the covering effect of the two smaller mirrors 2,3.

All advantages of the three-lamp illuminator shown in Fig. 3 can be exploited if it is mounted at a height of at least 5 metres.

However, the lamps are often mounted not more than 4 metres up for illuminating commercial premises, catering premises, schools, studios, rooms for cultural or social purposes, small workshops and so forth. In this case, an arrangement can advantageously be employed in which the mirrors 2,3 are turned towards the space to be illuminated as shown in Fig. 1 and the lamp 1 is covered with a diffuser 38 which is of light diffusing material or has a light diffusing surface. The relations of the main dimensions and the radii of curvature of the diffuser are adjusted to the proportion of main demensions of the space to be illumi nated, i.e. to the relation between the width 40, the length 41, and the height 42 of the space to be illuminated shown in Fig. 5, e.g.

as follows:

(a) If the space to be illuminated has a square or approximately square base, i.e.

width 40 is equal to or approximately equal to 115 length 41 and height 42 is at least half of the width 40, then the diffuser 38 has a hemi spherical shape.

(b) If the space to be illuminated has a square or approximately square base but its height 42 is less than half of the width 40, then the diffuser 38 has a round, lens-like shape and the smaller the height 42 is relative to the width 40, the flatter is the diffuser.

(c) If the space to be illuminated has a rectangular base, the diffuser 38 has the shape of an ellipsoid of rotation in which the ratio of the main axes are in the same propor tions as the main dimensions of the space to be illuminated.

In these examples, the lamp is arranged in the centre of the ceiling.

In this arrangement the light diffuser 38 can advantageously be produced from the radiating mass of Lambert.

If two such lighting sources according to the invention are placed parallel and adjacent to one another, or if they come into contact at the external edges 37 of the two smaller mirrors 2,3 as shown in Fig. 8, then a simple addition is obtained as regards the space to be illuminated. Additionally, however, quite unexpected advantages are achieved, as follows.

Usually, gas discharging lamps, including shortarc metal-halogenide lamps, can only be operated with a current limiting adapter. The conventional method of AC supply is shown in Fig. 9, where the parallel connected lamp 1 and ignition lamp 13 are connected, in series with a choke-coil 15, to the mains supply, and the reactive power of the choke-coil 15 is compensated with the reactive power of the capacitor 14 connected in parallel with the lamps 1 and 13. The stationary operational conditions of the lamp 1 are illustrated in Fig. 11, where the arc ignites at moments 16,18, and goes out at the moments 17,19, as a function of the sinusoidal voltage U. Thus, the lamp 1 gives light only during time sections 16-17 and 18-19, resulting in a very strong dark modulation of the light. By assembling two light sources together as described above, e.g. according to Fig. 8 and connecting them to the mains supply according to the circuit scheme shown in Fig. 10, i.e. one lamp 55 with the capacitor 14, the other lamp 56 with the choke-coil 15 are serially connected, and these two branches are connected parallel to the mains supply, as well as connecting the ignition lamps 51,52 filled with inert gas in parallel with the respective lamps 55,56 in a conventional manner, the operational conditions of the lamps 55, 56 will be quite different, as shown in Fig. 12. Namely, the arc of the lamp 55 ignites at the moments 20,24 and goes out at the moments 22,26 of the operational voltage U, and the arc of the lamp 56 ignites at the moments 21,25, and goes out at the moments 23, 27 of voltage U, according to when the instantaneous charging voltage reaches the voltage required to induce the arc. Thus, for the lamp 55 the arc ignites at moments 20,24, of the voltage U in Fig.

12, and then, as the capacitor 14 discharges, the arc goes out at the moments 22,26 of the voltage U in Fig. 12. As the inductive current lags 90' relative to the capacitive current, the magnetic energy of the chokecoil 15 also ignites lamp 56 after the ignition of lamp 55, illustrated at moments 21, 25 of the voltage U in Fig. 12, and then this arc goes out at the moments 23,27. Accordingly, the dark time intervals are restricted to the interval 23-24 being much shorter by appropriately chosen 4 GB 2 151 418A 4 adapters, than the interval 17-18 of a single lamp shown in Fig. 11. Thus light modulation can be decreased to a negligible degree, having regard to the persistence of vision of the 5 eyes.

The operational conditions can be further improved, i.e. the degree of light modulation and the power consumption can further be decreased by connecting a regulator unit 28 serially with the capacitance of the two-lamp circuit, i.e. capacitor 14, as shown in Fig. 13. A block diagram of this regulating unit 28 is shown in Fig. 14. The regulator unit 28 comprises in the foremost part a voltage am- plitude sensor 29 connected directly to the mains supply, and, connected serially, a current intensity sensor 30 and a controllable switching element 32, the break angle of which can be regulated by a signal received at the input of the regulator. This control signal is formed from the output signals of the voltage amplitude sensor 29 and the current intensity sensor 30 by an expanded multiplier circuit 31, by connecting the input terminals of the expanded multiplier circuit 31 to the output terminals of the voltage amplitude sensor 29 and the current intensity sensor 30. The maximum break angle that can be achieved and the control signal for the con- trollable switching element 32 responsible for the break angle are formed by the expanded multiplier circuit 31, based on a comparison with a reference signal. Comparing the luminous flux diagram 1 shown in Fig. 15 to the luminous flux diagram formed in an unregulated state shown in Fig. 12, it is well demonstrated that this solution also decreases the degree of light modulation along with reactive power consumption. The most important feature in Fig. 15 is that the lamp 56 of the circuit containing inductance ignites only when the arc of the lamp 55 in the capacitive circuit has just gone out, i.e. the two lamps can never light simultaneously. Thus, no illu- mination modulation can occur in the luminous flux, as can occur in Fig. 12 providing that the values of capacitance and inductance are not assorted.

This light modulation can most effectively be minimized by directing the luminous fluxes of the two co-operating lamps 55 and 56 onto the same surface by the large focussing mirrors 4 and, respectively, by inserting both lamps 55 and 56 into diffuser 38 or by arranging two adjacent diffusers each containing one lamp 55 and 56 respectively.

Claims (2)

1. A circuit comprising two gas discharge lamps arranged in parallel with one another, and a single capacitor and a single choke-coil, wherein the first lamp is connected serially only with the capacitor while the second lamp is supplied from the power supply in a serial connection with only the choke-coil.

2. A circuit as claimed in claim 1, in which in one of the lamp branches the serial reactive element, advantageously the capacitor, is serially connected with a regulating unit compris- ing a voltage amplitude sensor, a current intensity sensor and a controllable switching element connected to the signal output of an expanded multiplier circuit, while the input terminals of the expanded multiplier circuit are connected to the output terminals of the current intensity sensor and the voltage amplitude sensor, the regulating unit being connected across the terminals of the power supply.

Printed in the t)nited Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1985, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.