Electric lamp and discharge devices: systems – With radiant energy sensitive control means – Radiant energy control of an electric discharge device in...
Patent
1998-05-20
1999-11-02
Shingleton, Michael B
Electric lamp and discharge devices: systems
With radiant energy sensitive control means
Radiant energy control of an electric discharge device in...
315158, 250205, H05B 3702
Patent
active
059777176
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to lighting control systems and in particular lighting control systems utilising photoelectric means to sense light intensity levels, such as are used to control street lighting automatically.
With conventional lighting control systems which use photoelectric control, a photoelectric sensor is used which is separate from the switching circuit.
With conventional street lighting systems using photoelectric control, the lights are normally set to switch on at dusk when the light intensity falls below a first predetermined value and switch off at dawn when the light intensity rises above a second predetermined value. Because the street lights take time to reach full intensity, the first predetermined value is normally greater than the second predetermined value.
If at dusk, after the lights have switched on, the light intensity level rises again above the first predetermined value, the lights will switch off and similarly at dawn, if after the lights have switched off, the light intensity level falls again below the second predetermined value, the lights will switch on again. As a consequence, the system is sensitive to transient light intensity variations which would cause the lights to repeatedly switch on and off as dusk and dawn approach.
In order to overcome this problem, switching of the system is subject to significant time delays, for example of the order of 15 to 30 seconds, so that at dusk the lights will not switch on until the light intensity has remained at or below the first predetermined level for the delay period, and at dawn the lights will not switch off until the light intensity has remained at or above the second predetermined level for the delay period.
This system has the drawback that the switching on of the lights is delayed for a significant period during which light levels may deteriorate substantially. This then affects the accuracy of the control.
According to one aspect of the present invention a lighting control system comprises a photosensor, comparator means and a logic switching circuit, wherein the photosensor produces an output which is a function of the light intensity level, the comparator means being adapted to compare the output from the photosensor with a plurality of preset levels and to produce a logic output which controls the switching of the logic switching circuit between a plurality of states.
Preferably the lighting control system is in the form of an integrated circuit.
According to a preferred embodiment of the invention the light falling upon the photosensor is filtered to provide a response from the photosensor which is close to the human eye.
According to a further aspect of the present invention the logic switching circuit has four states; the logic switching circuit being in a first state when the light intensity is above a first predetermined value;
the logic switching circuit going from its first state to a second state when the light intensity falls below a second predetermined value;
the logic switching circuit going from its second state to a third state when the light intensity falls below a third predetermined value;
the logic switching circuit going from its third state to a fourth state when the light intensity rises above a fourth predetermined value;
the logic switching circuit going from its fourth state to its third state when the light intensity falls below a fifth predetermined value;
the logic switching circuit going from its second state to its first state when the light intensity rises above a sixth predetermined value;
the fifth predetermined value being below the fourth predetermined value and the sixth predetermined value being above the second predetermined value.
Switching means is preferably provided for switching the lighting system on when the logic switching circuit is in its second and third states and switching the lighting system off when the logic switching circuit is in its first and fourth states.
With the above system, the first state of the logic switching circuit corresponds to normal daylig
REFERENCES:
patent: 3965388 (1976-06-01), Brisk
patent: 4697122 (1987-09-01), Hoffer
Royce Thompson Limited
Shingleton Michael B
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