GB2530298A

GB2530298A - Light sensor

Info

Publication number: GB2530298A
Application number: GB1416501.3A
Authority: GB
Inventors: Lawrence Baynham; Tom Baynham
Original assignee: INDO LIGHTING Ltd
Current assignee: INDO LIGHTING Ltd
Priority date: 2014-09-18
Filing date: 2014-09-18
Publication date: 2016-03-23
Anticipated expiration: 2034-09-18
Also published as: GB201416501D0; GB2530298B

Abstract

A light sensor suitable for use with a light assembly 2 includes a light receiver 18 and a controller 16 connected to the light receiver, wherein the light receiver receives a light input including ambient light and converts the light input into an output signal and the controller receives the output signal. The controller calculates the level of ambient light either by determining the level of light emitted by the light assembly by monitoring a modulated component of the light input and subtracting it from the total light input, or by only calculating the level of ambient light incident on the sensor when the light assembly output is substantially zero, which may be determined from knowledge of a pulse frequency of the light assembly.

Description

Light Sensor The present invention relates to light sensors, light assemblies, such as lamps, including light sensors and replacement lighting units.

Many different types of street furniture exist such as streetlights and road sign lights. These incorporate a variety of lighting technologies such as fluorescent, high intensity discharge, induction lighting, light emitting diodes (LED5) and plasma lighting. Some of these include photocells which sense dawn and dusk so turning off the light during daylight hours and turn it back on during the night. The photocells are usually positioned away from the light source and light from passing vehicles so that they measure the actual ambient daylight, i.e. their sensitivity is not affected by the light source and light from passing vehicles. In examples of the known light assemblies, the photocell is mounted on an upwardly facing surface of the assembly housing, where it is shielded from the light emitted by the light assembly.

It is also known to replace fluorescent tubes with longer lasting and more energy efficient LED tubes. It is also known to retro fit photocells but this is a time consuming process.

According to a first aspect of the invention, there is provided a light sensor suitable for use with a light assembly, wherein the light sensor includes a light receiver and a controller connected to the light receiver, wherein the light receiver receives a light input including ambient light, the light receiver being adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the light assembly, and wherein the controller calculates the ambient light level by (i) subtracting the data relating to the light emitted by the light assembly from the light input where the data relates to an output from the light assembly; and/or (ii) calculating the ambient light level only when the output from the light assembly is substantially zero, where the data relates to a pulse frequency of the light assembly and the pulse frequency includes an off period.

It will be appreciated that reference herein to "ambient light" is intended to refer to natural daylight in the absence of any light component that is generated by a non-natural source.

Furthermore, reference to "includes data" refers to components within the controller which may have pre-determined parameters relating to the light emitted by the light emitting elements, such as components (e.g. filters) to detect modulated light, or to a memory which stores data relating to the light emitting elements.

In this aspect of the invention, the light sensor is substantially unaffected by the light output from the light assembly, as the contribution from the light emitting element(s) of the light assembly is either subtracted from the total light received by the light receiver or the ambient light levels are only calculated when the pulsed output from the light emitting element(s) is in an "off" state. This allows the ambient light to be calculated more accurately and also allows a greater flexibility in the positioning of the light sensor.

The controller may include data relating to the light output from the or each light emitting element of the light assembly, which may then be subtracted from the light input to calculate the ambient light levels. Thus, the data may relate to a light intensity which is emitted by the light assembly, for example a modulated light intensity. This is usually referred to as the illuminance, luminous emittance or luminous flux and maybe measured by the SI unit lux. In such an embodiment, the controller may include a first component adapted to detect the total light input received by the light receiver; a second component adapted to detect the total modulated light received by the light receiver; and a third component adapted to subtract the modulated light detected by the second component from the total light detected by the first component.

Additionally or alternatively, the controller may store data relating to the frequency of the light output from the light emitting element(s), where the light emitting element(s) emits a pulsed light output, such that the ambient light levels are sensed or measured when the light emitting element(s) is in an off state. For example, the sensor may continuously sense the light intensity received by the light receiver and the controller may include a filter adapted to remove or subtract the signal received when the light emitting element(s) are energised.

In an embodiment of the invention) the controller is capable of generating an electrical output signal and the controller is adapted to output the electrical output signal only when the calculated ambient light level is below a pre-determined threshold. Thus, when the ambient light level drops below a pre-determined threshold value, the electrical output signal of the controller causes the one or more light emitting elements to be energised. The electrical output signal from the controller may be received by a separate light emitting element main circuit which causes the light emitting element(s) to be switched on or off, or the controller may function as an inline switch, wherein it has an electrical output connected directly to the light emitting element(s). The controller may also switch off or cause to be switched off the light emitting element(s) when the ambient light level increases beyond a second threshold value. The first and second threshold values may be the same or different. Suitably, the second threshold value is higher than the first threshold value. In an embodiment of the invention, the second threshold value is greater than the light output from the light assembly.

In a further embodiment of the invention, the controller includes a time delay circuit, whereby the controller only outputs an electrical output signal when the measured or calculated ambient light level is below the first threshold value for a pre-determined period of time. Additionally or alternatively, the time delay circuit may control the electrical output signal from the controller.

Thus, the controller may cease to output an electrical output signal (i.e. switch off the light emitting element(s)), or output a second or "off" signal, only when the measured or calculated ambient light level is above the second threshold value for a pre-determined period of time.

These options help to prevent false positives and/or false negatives where temporary cloud cover reduces ambient light levels or extraneous light sources (such as from vehicle headlights) temporarily increase the light input. It is noted that it is difficult to filter out certain extraneous light sources, such as vehicle headlights and as such, the time delay circuit is useful to reduce or prevent so-called "nuisance switching".

In an embodiment of the invention, the time delay circuit has a time delay recovery rate which is asymmetrical. Suitably, the time delay circuit recovers much quicker to a reduction in ambient light levels (i.e. to energising the light emitting element(s)) than to an increase in ambient light levels (i.e. to switching off the light emitting element(s)). Accordingly, the controller is quicker to switch on the light emitting element(s) than it is to switch them off.

The light receiver is suitably adapted to receive light only in the wavelength range of 700nm to 1 mm, namely the infra red region of the electromagnetic spectrum. Suitably, it receives light only in the range 700 to l200nm, optionally only in the range 750 to llOOnm. Thus, the light receiver may include a filter which filters out light having a wavelength outside of the infra red region, specifically the near infra red region. It is known that LED elements emit relatively little light beyond 7SOnrn, so when the light assembly includes one or more LED elements, the light contribution to the light input from the LED element(s) is relatively low. -1,

The optional combination of a filter to select only light in the infra red portion of the electromagnetic spectrum and a controller able to calculate ambient light levels in the presence of modulated (i.e. pulsed) light sources by subtracting any emitted modulated light from the total light received by the receiver results in a much more accurate measurement of the true ambient light levels. It also allows cheaper filters to be used. Filters which can accurately filter out light from outside a specific region within the electromagnetic spectrum tend to be relatively expensive. On the other hand, filters which are economically viable in apparatus such as the present invention may not accurately filter out light having a pre-determined range of wavelengths. The combination of the filter with the controller of the present invention allows for cheaper filters to be used, as any unfiltered light from the light emitting element(s) is excluded by the controller from the total light levels received by the light sensor.

The further optional combination of a controller which is able to ignore a contribution to the total light levels of an AC powered light source, a filter which is able to filter out light having a pre- 1 5 determined range of wavelengths) and a time delay circuit that is able to ignore the effects of transient increases or decreases in the light received by the light receiver provides an accurate system for measuring ambient light levels and controlling light emitting element(s) in response to the measured ambient light levels.

According to a second aspect of the invention, there is provided a method of sensing ambient light in a light assembly, the method including (i) providing a light sensor including a light receiver and a controller connected to the light receiver, wherein the light receiver receives a light input including ambient light; (ii) providing the controller with data relating to a light output from the light assembly; (iii) converting the light input into a light receiver output signal; (iv) transmitting the light receiver output signal to the controller; and (v) calculating the ambient light level by (a) subtracting the data relating to the light emitted by the light assembly from the light input where the data relates to an output from the light assembly; or (b) calculating the ambient light level only when the output from the light assembly is substantially zero, where the data relates to a pulse frequency of the light assembly and the pulse frequency includes an off period.

According to a third aspect of the invention, there is provided a light assembly or luminaire including one or more light emitting elements and a light sensor as defined anywhere hereinabove.

In an embodiment of the third aspect of the invention, the or each light emitting element and the light sensor are carried by or located on a common substrate. This may be a PCB or similar substrate. By mounting the light emitting elements and the light sensor on a common substrate, a compact arrangement is provided. This is useful where the light assembly is intended to form a replacement unit for an existing lighting assembly, such as a replacement lamp or light bulb.

It will be appreciated that the or each light emitting element may be mounted on a primary substrate and the light sensor may be located on a secondary substrate, where the secondary substrate may be carried by the primary substrate. In this case, the light sensor and the light emitting element(s) are considered to be located on a common substrate (the primary substrate).

For example, the secondary substrate may include a plug or socket which engages a complementary socket or plug carried by the primary substrate. Such an arrangement is useful where the light sensor is assembled separately and may be used in connection with a number of different primary substrates. Thus, the secondary substrate carrying the light sensor may be plugged into or onto the primary substrate and the primary substrate forms the common substrate.

The assembly suitably includes an alternating current electrical input. Such AC inputs are common in street lighting and other lighting applications and this allows the assembly to be compatible with existing electrical inputs. In such embodiments, the assembly may include a rectifier to provide an electrical input which is compatible with suitable light emitting elements, such as LEDs.

An AC electrical input through a rectifier typically produces a light assembly having a pulsed output, although the frequency of the pulses tend to be sufficiently high that the human eye is unable to detect any significant flicker or pulsing of the light output. In such embodiments, namely where the or each light emitting element has a pulsed output with an on configuration and an off configuration, the controller may include data relating to the pulse frequency of the or each light emitting element, and it may calculate an ambient light level by only converting the light input into the output signal when the or each light emitting element is in an off configuration. Thus, the light sensor may effectively only measure the light input when the light emitting elements of the light assembly are in an off or non-emitting state. Alternatively, the controller may include a component that is able to identify a pulsed or modulated light signal such that the contribution of the modulated light to the total light received by the receiver can be subtracted from the total light received to provide a more accurate calculation of the ambient light levels.

In view of the above, the or each light emitting element may be an LED.

According to a fourth aspect of the invention, there is provided a replacement lighting unit comprising a translucent housing including at least one electrical connection passing through the housing and located within the housing at least one light emitting element, and a light sensor comprising a light receiver and a controller; wherein the controller is connected to a lighting circuit adapted to power the or each light emitting element in use, and to the light receiver; and the controller is adapted to energise or cause to be energised the or each light emitting element only when the ambient light level is below a pre-determined threshold value. Suitably, the housing is adapted to have a size and configuration which is substantially identical to the lighting unit it is replacing. In this way, the replacement lighting unit is able to fit within an existing light fitting with little or no modification to the fitting.

It is known that there is a move to replace existing light bulbs with replacement units having a lower energy consumption. However, there are often issues associated with replacing one technology with a different technology, such as the nature of the electrical input to the light unit, the size and configuration of the fitting(s) and the control of the replacement lighting unit. The lighting unit of the fourth aspect is intended to address and/or ameliorate one or more of these issues.

In view of the foregoing, the replacement lighting unit may be a replacement bulb. Suitably, the replacement bulb includes one or more electrical connections of the same size and configuration as the bulb it is replacing. In this way, a simple, energy inefficient bulb can be replaced with an energy efficient bulb.

Moreover, by providing a replacement light unit which includes at least one light emitting element and a light sensor, it is possible to convert a simple lighting assembly which may be on for twenty four hours a day) regardless of the ambient light levels, into a "smart" light assembly which is able to regulate its light output dependent on the levels of ambient light sensed by the sensor, simply by changing the lamp element (e.g. the bulb).

In an embodiment of the invention according to the fourth aspect, the light receiver receives a light input including ambient light, the light receiver being adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the or each light emitting element, and wherein the controller calculates the ambient light level by (i) subtracting the data relating to the light emitted by the or each light emitting element from the light input where the data relates to an output from the or each light emitting element; or (ii) calculating the ambient light level only when the output from the or each light emitting element is substantially zero, where the data relates to a pulse frequency of the light emitting element(s) and the pulse frequency includes an off period. Thus, the replacement lighting unit of the fourth aspect of the invention may include a light sensor according to the first aspect of the invention.

Suitably, the controller is capable of generating an electrical output signal relating to an "ON" configuration of the LEDs and the controller is adapted to output the electrical output signal relating to an "ON" state only when the calculated ambient light level is below a pre-determined threshold. As noted above, the electrical output signal may act as a control switch for a separate lighting circuit or it may directly energise the or each light emitting element.

The light receiver of the invention may receive light in the infra red portion of the electromagnetic spectrum, namely in the range 700nm to 1mm or in a narrower range of wavelengths as discussed above. Thus, the light receiver may include a filter which filters out light having a wavelength outside of the infra red region. As noted above, LEDs, for example, emit very little light having wavelengths above 750nm.

In an embodiment of the fourth aspect of the invention, the controller may include a time delay circuit which is adapted to exclude transient increases or decreases in the sensed light levels.

As with the aspects of the invention mentioned hereinabove, the or each light emitting element and the light sensor may be located on a common substrate.

In an embodiment of the invention, the unit is adapted to receive an AC input and includes a rectifier.

Suitably, the or each light emitting element of the replacement lighting unit is an LED.

The skilled person will appreciate that the features described and defined in connection with the aspect of the invention and the embodiments thereof may be combined in any combination, regardless of whether the specific combination is expressly mentioned herein. Thus, all such combinations are considered to be made available to the skilled person.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure la is a schematic representation of a light assembly according to the second aspect of the invention which includes a light sensor according to the first aspect of the invention; Figure lb is an enlarged schematic representation of the light receiver and the controller; and Figure lc is a schematic representation of the controller.

For the avoidance of doubt, the skilled person will appreciate that in this specification, the terms "up", "down", "front", "rear", "upper", "lower", "width", etc. refer to the orientation of the components as found in the example when installed for normal use as shown in the Figures.

The light assembly 2 includes four high voltage LEDs 4 connected in series and controlled by an LED power circuit 6, driven directly from a rectified AC mains power supply 8 having a mains AC power source 10. In the context of this embodiment, the term "high voltage" refers to LEDs having a string forward voltage of between 200-260V, i.e. equivalent to a mains electrical voltage.

The power supply 8 includes a control circuit which is discussed below. This embodiment of the invention is intended to be a retrofit product designed to work, with minimal modification, to an existing fluorescent control gear and improve efficiency and reliability. The light output has a significant content of 100Hz flicker, which is a pre-existing condition with the original fluorescent based products. The principle is applicable to other configurations of LED light sources or other light sources, the basic difference being in the switching control interface for particular configurations and means of powering the analog signal conditioning circuitry.

The LEDs 4 are mounted on a primary printed circuit board assembly (PCB) 12. Also mounted on the primary PCB 12 is a secondary printed circuit board assembly (PCB) 14 which carries a controller 16 and a light receiver 18. The light receiver 18 includes a filter (not shown) that excludes light having a wavelength less than about SOOnm or greater than about 1050nm. The secondary PCB 14 plugs onto the primary PCB 12 and is electrically connected to a power output 20a, 20b from the power supply 8 and also to a control circuit 22 within the power supply 8 which functions as a biasing circuit. The control circuit 22 controls the LED power circuit 6.

The external light levels are monitored by the light receiver 18 which comprises a PIN photodiode and an infrared bandpass filter (800 -1050nm) and so responds only to the near infrared content of daylight. The LEDs 4 emit very little IRradiation beyond 750nm and this is predominantly modulated by the rectified supply frequency of 100Hz based on a mains electrical alternating current having a frequency of 50Hz. The flicker resulting from the 100Hz twice supply frequency is a characteristic not present in daylight, so it is possible to subtract the light contribution of the LEDs from the total light received by the light receiver whether the LEDs 4 are illuminated or not.

The photodiode generates an output signal 26 to the controller 16 in the form of an output current which is linearly proportional to the incident IR radiation. Accordingly, the output signal 26 is proportional to the total incident radiation received by the light receiver 18.

The next stage of the process in this embodiment is to remove the contribution to the total incident radiation that is attributable to the LEDs themselves or to other modulated light sources located near to the light assembly 2.

The controller 16 firstly converts the output signal current to a corresponding voltage via an operational amplifier 24 via analog processing circuitry. The amplified signal is filtered by a low pass filter 28, which detects the average IR light level, and a peak detector filter 30, which detects the peak value of all light content having a modulation frequency, where the modulation frequency is below about 500Hz. The controller then subtracts from the steady state averaged value the peak value of the modulated light received via a subtractor 32. Thus, the subtractor 32 generates an average voltage level which relates to the external light level and is substantially devoid of the internally generated IR signal from the LEDs 4. In this way, any light emitted by the LEDs 4 in at least part of the electromagnetic spectrum not usually associated with light emitted by the LEDs 4 and having characteristics not present in ambient daylight is detected by the photodiode, but then effectively removed by the controller.

Following the removal of any light contribution from the LEDs 4 (together with the contribution from any additional modulated light sources in the vicinity of the light sensor) detected by the filtered photodiode, the light assembly 2 removes transient increases in light levels associated with non-modulated light sources, such as vehicle headlights.

In this respect, the controller 16 further includes a time delay circuit 34 that responds very slowly (in the region of 30 seconds -the actual delay can be tailored to the site requirements by component changes) to an increase in the received levels of IR radiation but rapidly to a falling trend. This is to avoid nuisance switching off at night by passing vehicle headlights, whose tungsten filament bulbs have a significant IR content.

An output signal 36 from the delay circuit 34 is received by a threshold detector 38 which also forms part of the controller. The threshold detector 38 includes a precision voltage reference which compares the voltage signal 36 to a defined pre-detemined level set within the detector 38. A significant amount of hysteresis is included within the threshold detector 38 for the following reasons. Firstly, it is to avoid jitter when turning off at dawn and on at dusk. The threshold levels can be modified by changes of component value to accommodate required variations of lux level for the particular application and mounting position. Secondly, the hysteresis is also set to ensure that the illumination when switching on the LEDs 4 is insufficient to cause a subsequent turn off by detection of a residual IR signal from the LEDs. These levels take into account the fact that many of the applications use twinned tubes in fittings and, as independent integrated daylight switching units, they will inevitable turn on and off individually at slightly different daylight conditions due to manufacturing tolerances.

The threshold detector 38 sends a control signal 40 to the LED control circuit 22 within the power supply 8, to control the switching action of the LEDs 4. Hysteresis is thus used to control the switching and prevent the small amounts of electromagnetic radiation emitted from the light source turning the light source off, whereby the level of electromagnetic radiation in theIR region required to switch the light source off in the morning is higher than that emitted by the light source.

The light assembly 2 described herein is designed to replace a fluorescent tube. Thus, the primary PCB 12 is suitably located within a common translucent or transparent housing having an elongate structure with electrical contacts at each end, or one end only, to receive electrical power. In this way, a simple, minimally controlled fluorescent tube may be replaced with a more energy efficient "smart" bulb which contains its own control circuitry and which switches the LEDs on and off in response to sensed ambient light conditions.

In an alternative embodiment, rather than subtracting the incident IR radiation which has a flicker frequency of 100Hz, the controller only processes the output signal from the photodiode when the rectified supply voltage to the LEDs is below a minimum threshold value to energise the LEDs.

This may be achieved by including in the controller 16 a filter which subtracts or ignores the light received by the photodiode when the LEDs 4 are energised. LEDs powered by a rectified AC power source have an "on" phase when the rectified supply voltage exceeds a threshold value and an "off' phase when the rectified supply voltage drops below the threshold level. Thus, the photodiode output signal is only processed when the LEDs are in an "off' phase of their pulsed operation.

The invention may take a form different to that specifically described. For example the light source could be other than LEDs. The sensor switch could be separate to the light source rather than mounted in a common housing. The photodiode could be adapted to detect electromagnetic radiation other than infra red radiation if the light source emitted radiation other than substantially non infra red radiation.

Further modifications will be apparent to those skilled in the art without departing from the scope of the present invention as defined herein.

II

Claims

Claims 1. A light sensor suitable for use with a light assembly, wherein the light sensor includes a light receiver and a controller connected to the light receiver, wherein the light receiver receives a light input including ambient light, the light receiver being adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the light assembly, and wherein the controller calculates the ambient light level by (i) subtracting the data relating to the light emitted by the light assembly from the light input where the data relates to an output from the light assembly; or (ii) calculating the ambient light level only when the output from the light assembly is substantially zero, where the data relates to a pulse frequency of the light assembly and the pulse frequency includes an off period.
2. A light sensor according to Claim 1, wherein the light input comprises light emitted by the light assembly and ambient light, the data relates to the intensity of the light emitted by the light assembly, and wherein the controller calculates the ambient light level by subtracting the data relating to the light emitted by the light assembly from the light input.
3. A light sensor according to Claim 1, wherein the light input includes ambient light and a pulsed light output from the light assembly, the pulsed light output includes an off period in which no light is emitted by the light assembly, the data relates to the pulse frequency, and the controller only calculates the ambient light level only when the pulsed light output is in its off period.
4. A light sensor according to any of Claims ito 3, wherein the controller is capable of generating an electrical output signal and the controller is adapted to output an electrical output signal only when the calculated ambient light level is below a pre-determined threshold.U
5. A light sensor according to any of Claims ito 4, wherein the light receiver is adapted to receive light in the wavelength range 700nm to 1mm.
6. A light sensor according to any of Claims ito 5, wherein the controller includes a time delay circuit.
7. A light assembly including one or more light emitting elements and a light sensor according to any of Claims ito 6.
8. A light assembly according to Claim 7, wherein the or each light emitting element and the light sensor are located on a common substrate.
9. A light assembly according to Claim 7 or Claim 8, wherein the assembly includes an alternating current input.
10. A light assembly according to Claim 9, wherein the assembly includes a rectifier.
ii. A light assembly according to Claim 9 or Claim 10, wherein the or each light emitting element has a pulsed output with an on configuration and an off configuration; wherein the controller includes data relating to the pulse frequency of the or each light emitting element, and wherein the controller calculates an ambient light level by subtracting modulated light levels from a total light input received by the light receiver.
12. A light assembly according to any of Claims 7 to ii, wherein the or each light emitting element is an LED.
13. A replacement lighting unit comprising a translucent housing including at least one electrical connection passing through the housing and located within the housing at least one light emitting element, and a light sensor comprising a light receiver and a controller; wherein the controller is connected to the or each light emitting element and to the light 1-, receiver, and the controller is adapted to energise or cause to be energised the or each light emitting element only when the ambient light level is below a pie-determined threshold value and wherein the housing is adapted to have a size and configuration which is substantially identical to the lighting unit it is replacing.
14. A replacement lighting unit according to Claim 13, wherein the light receiver receives a light input including ambient light, the light receiver being adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the or each light emitting element, and wherein the controller calculates the ambient light level by (i) subtracting the data relating to the light emitted by the or each light emitting element from the light input where the data relates to an output from the or each light emitting element; or (ii) calculating the ambient light level only when the output from the or each light emitting element is substantially zero, where the data relates to a pulse frequency of the light emitting element(s) and the pulse frequency includes an off period.
15. A replacement lighting unit according to Claim 13 or Claim 14, wherein the controller is capable of generating an electrical output signal and the controller is adapted to output an electrical output signal only when the calculated ambient light level is below a pre-determined threshold.
16. A replacement lighting unit according to any of Claims 13 to 15, wherein the light receiver is adapted to receive light in the wavelength range 700nm to 1mm.
17. A replacement lighting unit according to any of Claims 13 to 16, wherein the controller includes a time delay circuit.
18. A replacement lighting unit according to any of Claims 13 to 17, wherein the or each light emitting element and the light sensor are located on a common substrate. jN19. A replacement lighting unit according to any of Claims 13 to 18, wherein the unit is adapted to receive an AC input and includes a rectifier.20. A replacement lighting unit according to any of Claims 13 to 19, wherein the or each light emitting element has a pulsed output with an on configuration and an off configuration; wherein the controller stores data relating to the pulse frequency of the or each light emitting element, and wherein the controller calculates an ambient light level by receiving a light input value from the light receiver when the or each light emitting element is in an off configuration.21. A replacement lighting unit according to any of Claims 13 to 20, wherein the or each light emitting element is an LED.Amendment to Claims have been filed as follows 1. A light sensor suitable for use with a light assembly, wherein the light sensor includes a light receiver and a controller connected to the light receiver, wherein the light receiver includes a filter such that it receives light on in the wavelength range 700nm to 1mm and it receives a light input in this range which includes ambient light and modulated light, the light receiver being adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the light assembly, and wherein (i) the data relating to the light emitted by the light assembly is the intensity of the modulated light received by the light receiver and the controller calculates the ambient light level by subtracting the intensity of the modulated light from the light input; or (ii) the data relating to the light emitted by the light assembly is the pulse frequency of the modulated light and the controller calculates the ambient light level only when the output from the light assembly is substantially zero; and wherein the controller is capable of generating an output signal and the controller is adapted to output an output signal only when the calculated ambient light level is below a pre-determined threshold. IC)2. A light sensor according to Claim 1 wherein the controller includes a time delay circuit. (4 r3. A light assembly including one or more light emitting elements and a light sensor according to Claim 1 or Claim 2.4. A light assembly according to Claim 3, wherein the or each light emitting element and the light sensor are located on a common substrate.S. A light assembly according to Claim 3 or Claim 4, wherein the assembly includes an alternating current input.6. A light assembly according to Claim 5, wherein the assembly includes a rectifier.7. A light assembly according to any of Claims 3 to 6, wherein the controller includes a first component adapted to detect the total light input received by the light receiver; a second component adapted to detect the total modulated light received by the light receiver; and a third component adapted to subtract the total modulated light detected by the second component from the total light detected by the first component.8. A light assembly according to any of Claims 3 to 7, wherein the or each light emitting element is an LED.9. A replacement lighting unit comprising a translucent housing including at least one electrical connection passing through the housing and located within the housing at least one light emitting element, and a light sensor comprising a light receiver and a controller; wherein the controller is connected to the or each light emitting element and to the light receiver, and the controller is adapted to energise or cause to be energised the or each light emitting element only when the ambient light level is below a pre-determined threshold value and wherein the housing is adapted to have a size and configuration which is substantially identical to the lighting unit it is replacing. IC)10. A replacement lighting unit according to Claim 9, wherein the light receiver includes a filter such that it receives light on in the wavelength range 700nm to 1mm and it receives a light input in this range which includes ambient light and modulated light, the light receiver being LI) adapted to convert the light input into an output signal and the controller being adapted to receive the output signal, wherein the controller includes data relating to the light emitted by the light assembly, and wherein (i) the data relating to the light emitted by the light assembly is the intensity of the modulated light received by the light receiver and the controller calculates the ambient light level by subtracting the intensity of the modulated light from the light input; or (ii) the data relating to the light emitted by the light assembly is the pulse frequency of the modulated light and the controller calculates the ambient light level only when the output from the light assembly is substantially zero; and wherein the controller is capable of generating an output signal and the controller is adapted to output an output signal only when the calculated ambient light level is below a pre-determined threshold, and wherein the or each light emitting element is energised in response to the output signal from the controller.11. A replacement lighting unit according to Claim 9 or Claim 10, wherein the controller includes a time delay circuit.12. A replacement lighting unit according to any of Claims 9 to 11, wherein the or each light emitting element and the light sensor are located on a common substrate.13. A replacement lighting unit according to any of Claims 9 to 12, wherein the unit is adapted to receive an AC input and includes a rectifier.14. A replacement lighting unit according to any of Claims 9 to 13, wherein the or each light emitting element is an LED. IC) (4 r IC) r