Demand responsive lighting control system and method

1. Alight control system for controlling a lighting system, wherein the light control system is arranged to receive a power reduction parameter (alpha), the light control system comprising:

a light controller ( 134 ) arranged to:

receive a measured light value from a light sensor,

determine a light channel level value depending on the measured light value and a calibrated setpoint value if no power reduction parameter has been received, and

determine a light channel level value depending on the measured light value and a scaled calibrated setpoint value if the power reduction parameter has been received, the scaled calibrated setpoint value being equal to the calibrated setpoint value multiplied by the power reduction parameter;

a load controller arranged to:

receive the light channel level value from the light controller,

determine an output level signal depending on the light channel level value if no power reduction parameter has been received and

determine a scaled output level signal if the power reduction parameter has been received, the scaled output level signal being equal to the output level signal multiplied by the power reduction parameter, and

send the output level signal or the scaled output level signal to drivers of light sources of the lighting system.

2. The light control system according to claim 1 , wherein the light controller is arranged to determine the light

TargetLux( t 0 )=SetPointCal

TargetLux( t 0 +1)=alpha*SetPointCal

with

SetPointCal being the desired light level in a controlled space,

TargetLux(t 0 ) being a targeted overall light level to be delivered to the controlled space, before applying the reduction parameter,

TargetLux(t 0 +1) being the targeted overall light level to be delivered to the controlled space, after applying the reduction parameter,

the light controller further being arranged to determine the light channel level by calculating:

LightChannelLevel( t )=(TargetLux−DL( t ))×LightChannelCal/SetPointCal

with

LightChannelLevel(t) being the light channel level determined at time t,

TargetLux being the targeted overall light level,

DL(t) being the daylight contribution sensed by the light sensor at time t, and

LightChannelCal being the light channel level determined during a calibration/commissioning process when the controlled space is kept at a desired light level.

3. The light control system according to claim 1 , wherein the load controller is arranged to determine the scaled output level signal by calculating:

LightOutput( t )=alpha*LightChannelLevel( t )

with

LightOutput(t) being the scaled output level signal at time t,

alpha being the power reduction parameter, and

LightChannelLevel(t) being the light channel level value at t.

4. The light control system according to claim 1 , wherein the load controller is arranged to determine the output level signal so that a difference between the output level signal of two consecutive steps is:

LightOutput( t )−LightOutput( t+ 1)=FadeStepPower*LightChannelLevel( t )+FadeStepDL( t )*alpha

with

LightOutput(t) being output level signal at step t,

FadeStepDL(t) being fade step of daylight regulation at step t,

FadeStepPower being fade step of the power reduction factor,

alpha being power reduction factor.

5. The light control system according to claim 4 , wherein a value for the parameter FadeStepPower is half the size of a daylight regulation fading step size used by the light controller.

6. A lighting system comprising the light control system according to claim 1 and a light sensor module, the light sensor module comprising the light controller and a photo sensor.

7. A lighting system comprising the lighting control system according to claim 1 , one or more light sources and one or more drivers for driving the light sources.

8. A method of operating a light control system for controlling a lighting system, the method comprising:

receiving a measured light value from a light sensor;

determining a light channel level value depending on the measured light value and a calibrated setpoint value if no power reduction parameter has been received;

determining a light channel level value depending on the measured light value and a scaled calibrated setpoint value if the power reduction parameter has been received, the scaled calibrated setpoint value being equal to the calibrated setpoint value multiplied by the power reduction parameter;

determining an output level signal depending on the light channel level value if no power reduction parameter has been received;

determining a scaled output level signal if the power reduction parameter has been received, the scaled output level signal being equal to the output level signal multiplied by the power reduction parameter, and

sending the output level signal or the scaled output level signal to drivers of light sources of the lighting system.

9. A computer program product downloadable from a network and/or stored on a computer-readable medium and/or microprocessor-executable medium, the product comprising program code instructions for implementing the method according to claim 8 when executed on a computer.