GB2133532A

GB2133532A - Light sensitive switch

Info

Publication number: GB2133532A
Application number: GB08300518A
Authority: GB
Inventors: Guilherme Ysenbout Mogas
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-01-10
Filing date: 1983-01-10
Publication date: 1984-07-25
Also published as: GB8300518D0

Abstract

A photosensitive switch for automatically dipping the headlights of a vehicle comprises a light dependent resistor 4 controlling the state of conduction of two cross coupled transistors T1 and T2 which control the operation of change-over relay 1 connected to the dipped and full beam circuits of the vehicle lighting system. A manually operable switch 5 is provided for the user to set whether the lights operate on full or dipped beam but this is overridden by the light dependent resistor 4 when the detected light level is in excess of a predetermined value. Thus in the presence of light from the headlights of oncoming vehicles, the vehicle headlights are automatically dipped and held in that condition but at other times the driver can select full or dipped beam. <IMAGE>

Description

SPECIFICATION Light sensitive switch This invention relates to a light sensitive switch and more particularly to such a switch for use in'controlling the full/dipped beam setting of vehicle headlights.

Drivers are frequently dazzled by the headlights of oncoming vehicles be set to fullbeam either due to carelessness or disregard for the law.

The present invention is concerned with the provision of a photosensitive switch to be fitted to the lighting system of a vehicle so that when the photosensitive switch detects more than a certain amount of light falling on it, the vehicle's headlight or headlights will automatically be dipped. This photosensitive switch may be arranged to respond to the light from oncoming vehicles so that the vehicle's headlight(s) dipped so as to avoid dazzling the other drivers and likewise the photosensitive switch may respond to street lighting or sky or sunlight in excess of a certain amount so as to dip the vehicle headlight(s) then also. Obviously this solution would be most satisfactory if all vehicles were to be fitted with such a switch but this would require legislation and international co-operation and before such could be achieved.

Obviously a cheap and reliable switch would have to be available. Embodiments of this invention can provide particularly simple and effective solutions to this problem.

In one practical form, the photosensitive switch includes a light dependent resistor or other photosensitive devices electrical characteristics are affected by the amount of light falling on it, arranged to control a change-over relay or equivalent device having a common terminal connected to the vehicle supply line and two output contacts, one of which is made when the headlight(s) is to operate on dipped beam and the other to be made when the headlight(s) is to operate on full beam, the arrangement being such that the dipped beam contact is made when the photosensor detects a light level in excess of a predetermined value and so that when the detected light is below this level, the dipped or full beam may be selected by the user.For this purpose, a manually operable switch may be provided to enable the user to select dipped or full beam but the circuit is preferably arranged so that this switch is overridden when the predetermined light level detected by the photosensor is exceeded so that in those circumstances the headlight(s) is always on dipped beam. Where the vehicle already has such a change-over relay, the photosensitive switch may include a suitable controlled conduction element such as a transistor or thyristor to appropriately control the state of this relay.

More specifically, in one embodiment, the photosensitive switch may comprise a pair of transistors such as ordinary bi-polar, cross coupled in a bi-stable configuration with the relay being in the collector circuit of one of the transistors to be controlled thereby. The light dependent resistor or other photosensitive element may be connected to control the state of conduction of the other of the two transistors. In those circumstances, the manually operable switch for the user to select full or dipped beam may be connected to control the state of conduction of the first transistor, whose load is the relay, with the circuitry being suitable biased so that the manual switch is overridden by the photosensor when the photosensor detects a light level in excess of the predetermined value.

The invention will be further described by way of example with reference to the accompanying drawings in which the sole figure is a circuit diagram of one embodiment of the present invention.

The photosensitive switch embodying the present invention shown in the figure comprises a pair of PNP transistors T1 and T2 cross coupled in a bi-stable configuration by four resistors, R1-R4. The coil 1 of the change-over relay 2 is in the collector circuit of transistor T2 so that the state of the relay contact is controlled by the state of conduction of transistor T2. The relay has a common contact C which is connected to one of the supply lines from the vehicle battery 3, a normally-closed contact D connected to the full-beam terminal of the headlight or headlights and a normally open contact E connected to the dipped beam contact of the headlight(s).

The operation of the circuitry is controlled by a light dependent resistor 4 whose resistance falls as the light incident thereon increases.

The emitters of transistors T1 and T2 are connected together and to the positive side of the vehicle battery 3 via a resistor R5.

The values of the resistors R1-R5 are chosen in relation to one another and the light and dark resistance is of the light dependent resistor 4 so that when the light falling on LDR 4 exceeds the value at which it is desired to dip the headlights, the transistors T2 is turned on and held on. For this purpose, the LDR 4 is preferably located on the vehicle so that it "sees" at least approximately what the driver sees when looking forward from the vehicle. In the case of a car or lorry, the LDR 4 can thus be located within the passenger compartment or cabin at about eye level and directed forwards through the vehicle windscreen. Other sitings are possible although it is, of course, important that it be shielded from the vehicle's own lights.The LDR 4 may be provided with a shield or optical arrangement both to enhance its response to light from oncoming vehicles and to diminish its response to light coming from other directions which might cause erroneous operation.

The circuitry also includes a switch 5 operable by the driver from the driving seat so that when the light detected by the LDR 4 is below the predetermined value, the transistor T2 is turned off so that the full beam headlights are energised. This change-over is, however, overridden by the LDR 4 when the threshold detected light level is exceeded so that the vehicle headlights are held on dipped beam.

It will thus be appreciated that the illustrated embodiment can achieve its objective of providing a simple and effective circuit to dip a vehicle's headlights in response to the light from the headlights of oncoming vehicles and it will also dip the vehicle headlights when the detected light level increases under other circumstances, such as when the vehicle is passing through street-lit areas.

Suitable component values for the circuit shown in the figure are as follows: R1-3300 Ohms Resistance R2-2200 Ohms Resistance R3-27000 Ohms Resistance R4-4700 Ohms Resistance R5-47 Ohms Resistance C 1-1 Ouf Electrolytic Capacitor C2-100uf Electrolytic Capacitor

Claims

1. A photosensitive switch for controlling the operation of the headlight or headlights of a vehicle, the photosensitive switch comprising a photosensor and change-over circuit responsive to the light level detected by the photosensor to energise the vehicle headlight or headlights selectively either at full beam or dipped beam depending on the detected light level, dipped beam being selected when the detected light level is below a predetermined value.

2. A photosensitive switch according to Claim 1 wherein the change-over circuit is a relay.

3. A photosensitive switch according to Claim 1 or 2 and including a user-operable switch arranged so that the user can set the vehicle headlight or headlights to full beam if, but only if, the light level detected by the photosensor is below a predetermined value.

4. A photosensitive switch according to Claim 2 or 3 and including a pair of transistors cross coupled in a bi-stable configuration, the relay being connected to respond to the state of conduction of one of the transistors and the photosensor being connected to control the state of conduction of the other of the two transistors.

5. A photosensitive switch according to any one of Claims 2 to 4 wherein the relay has a common, input contact connected to one side of the vehicle electrical supply, a first output contact connected to energised the vehicle headlight(s) at full beam and a second contact connected to energise the vehicle headlight(s) at dipped beam.

6. A photosensitive switch according to Claim 5 wherein the common contact makes with the first contact when the relay coil is de energised.

7. A photosensitive switch constructed and arranged to operate substantially as here it before described with reference to and as illustrated in the accompanying drawing.