Light Lightness Control Server

The Light Lightness Control (LC) Server controls a single Light Lightness Server instance on the same device with a state machine.

The state machine defines common behavior for a light fixture through three states, each with its own timing parameters and light levels. As input to its state machine, the Light LC Server listens for Sensor and OnOff messages.

In addition to the state machine, the Light LC Server may optionally use a regulator to control the ambient illuminance in the room. The regulator requires illuminance sensor readings acting as feedback for its regulator loop.

The Lightness Control Server is always disabled by default, and must be enabled by a Light Lightness Control Client.

Overview

In this section, you can find more detailed information about the following aspects of the Light LC Server:

Composition data structure

As both the Light LC Server and the Light Lightness Server extend the Generic OnOff model, the two models cannot be instantiated on the same element.

Note

Due to implementation limitations, the Light LC Server is instantiated on the next element after the Light Lightness Server it is controlling.

Light Lightness Control Server composition data structure

Light Lightness Control Server composition data structure

In the application, this composition data looks like this:

static struct bt_mesh_elem elements[] = {
   /* Lightness element */
   BT_MESH_ELEM(1,
       BT_MESH_MODEL_LIST(BT_MESH_MODEL_LIGHTNESS_SRV(&lightness_srv)),
       BT_MESH_MODEL_NONE),
   /* Light Control element */
   BT_MESH_ELEM(2,
       BT_MESH_MODEL_LIST(BT_MESH_MODEL_LIGHT_CTRL_SRV(&light_ctrl_srv)),
       BT_MESH_MODEL_NONE),
};

The Light LC Server will log an error during initialization if the controlled Lightness Server is on the same element.

Relationship with other nodes

When the Light LC Server model controls a Light Lightness Server, all nodes should publish to the LC Server or its extended Generic OnOff model, instead of publishing directly to the Light Lightness Server:

Light Lightness Control Server node organization

The dimmer devices that want to override the light level of the Lightness Server can publish directly to the Lightness Server. This disengages the Light LC Server, and the Lightness Server operates independently until the Light LC Server is explicitly re-enabled.

Lightness state machine

The Light LC Server’s lightness state machine operates in the following states:

Standby

There is no activity in the room, and the device’s light are either off or dimmed.

On

There is activity in the room, and the lights are on.

Prolong

There is no activity detected. The lights are at a slightly dimmed level, ready to get back to their On level as soon as activity is detected.

Each state has a lightness level and a transition time used for fading. When the state changes, the light level fades from the previous state’s level to the new state’s level in a transition time span determined by the new state.

When the Light LC Server is turned on, the following sequence takes place:

Light Lightness Control Server light levels

Light Lightness Control Server light levels

The state machine cycles through the states with the following events:

Timeout

Triggered when the current state has timed out. The state machine automatically moves into the next state.

On

Toggled when a motion sensor is triggered or the On button is pressed on a light switch.

Off

Toggled when the Off button is pressed on a light switch.

The On and Prolong states will start a timer as soon as the transition into the state is finished. When this timer expires, the state machine will automatically go into the next state. If the On event is triggered while in the On state, the timer is reset, and the transition to the Prolong state is postponed.

Light Lightness Control Server state machine

Light Lightness Control Server state machine

Note

The state machine only works while the Light LC Server is enabled, and it always starts in the Standby state.

Resuming the state machine operation

Whenever something but the Light LC Server interacts with the controlled Lightness Server, the Light LC Server disables its state machine, and the Lightness Server starts running independently. To resume the state machine operation, the Light LC Server must be explicitly re-enabled.

To avoid having a Lightness Server running independently forever, the Light LC Server implements a resume timer that lets the Light LC Server regain control after being disabled for a certain number of seconds. The resume timer can be configured with the CONFIG_BT_MESH_LIGHT_CTRL_SRV_RESUME_DELAY option, and is disabled by default.

Note

The resume timer does not exist in the Bluetooth mesh specification, and may become incompatible with future specification changes. Although it does not break the specification or qualification tests in the current iteration of the Bluetooth mesh specification, its behavior may be unexpected for third party devices, and should be used with caution.

State machine outputs

The state machine has two different output values for each state:

Light level

The light level decides the output light level sent to the controlled Light Lightness Server. Each state has a configurable light level, and the output light level will be the light level of the current state, with linear transitions between the states. The default light level values per state are:

  • Standby state - 0%

  • On state - 100%

  • Prolong state - 50%

Target illuminance level

Each state has a configurable target illuminance level, which is used as input to the Illuminance regulator. The target illuminance level decides the ambient illuminance the regulator should try to achieve, as measured by illuminance sensors nearby. Just like with the light level, the target illuminance always matches the configured target illuminance for the current state, with linear transitions between the states.

External event triggers

While the Timeout event is controlled internally, the On and Off events are produced by external behavior.

On event

The On event lets the Light LC Server know that there is activity in the room. It can be generated by light switches and sensors.

  • Light switches can implement one of the following models to send On messages that turn the Light LC Server on:

  • Occupancy sensors can also trigger the On event, depending on the current state and occupancy mode:

    • If the occupancy mode is enabled, sensor readings that indicate activity can trigger an On event at any time.

    • If the occupancy mode is disabled, sensors cannot turn the lights on, but they will still prevent lights from turning off.

The following sensor types can also trigger the On event:

Motion sensed - bt_mesh_sensor_motion_sensed

Any sensor value higher than 0 triggers an On event in the Light LC Server state machine. Messages with a value of 0 are ignored.

People count - bt_mesh_sensor_people_count

Any sensor value higher than 0 triggers an On event in the Light LC Server state machine. Messages with a value of 0 are ignored.

Presence detected - bt_mesh_sensor_presence_detected

Messages with a true value triggers an On event in the Light LC Server state machine. Messages with a false value are ignored.

Time since motion sensed - bt_mesh_sensor_time_since_motion_sensed

When the sensor’s Time since motion sensed value is lower than the Light LC Server’s occupancy delay, the Light LC Server starts a timer that expires at the time equal to Motion sensed plus occupancy delay. When this timer expires, an On event is generated.

Note

Only sensors reporting the Time since motion sensed type will be affected by the occupancy delay. Other sensor triggers are always instantaneous.

Off event

The Off event can only be generated by a light switch being turned off. It moves the Light LC Server into Standby, transitioning from the previous light level with the manual mode Standby fade time (BT_MESH_LIGHT_CTRL_PROP_TIME_FADE_STANDBY_MANUAL).

The Off event puts the Light LC Server into manual mode, which disables sensor input until the manual mode timeout (CONFIG_BT_MESH_LIGHT_CTRL_SRV_TIME_MANUAL) expires. This prevents the lights from turning back on by the movement of the person that presses the light switch.

Note

Unlike other timing parameters, the manual mode timeout is proprietary and cannot be reconfigured at runtime by other models in the mesh network.

Light switches can implement one of the following clients to send Off messages that turn the Light LC Server on:

If a Timeout transition from Prolong to Standby is already in progress, the Light LC Server will check whether the remaining transition time is shorter than the Off event fade time and will execute whichever is the fastest.

State machine configuration

Both the timing and output levels are configurable at compile time and at runtime:

  • The compile time configuration is done through the Light Control Server Kconfig menu options.

  • The runtime configuration must be done by a Light Control Client model instance through the Light Lightness Controller Setup Server.

Timing parameters

This section lists compile and runtime options to be used when setting timing parameters.

Delay from occupancy detected until light turns on
Transition time to On state
Time in On state
Transition time to Prolong state
Time in Prolong state
Transition time to Standby state (in auto mode)
Transition time to Standby state (in manual mode)
Manual mode timeout
Output parameters

This section lists compile and runtime options to be used when setting output parameters.

On state light level
Prolong state light level
Standby state light level
On state target illuminance
Prolong state target illuminance
Standby state target illuminance

Illuminance regulator

The illuminance regulator complements the light level state machine by adding an ambient illuminance sensor feedback loop. This allows the Lightness Server to adjust its output level that is based on the room’s ambient light, and as a result conserve energy and achieve more consistent light levels.

Light Lightness Control Server illuminance regulator

Light Lightness Control Server illuminance regulator

The illuminance regulator takes the state machine’s target illuminance level as the reference level and compares it to sensor data from an external illuminance sensor. The inputs are compared to establish an error for the regulator, which the regulator tries to minimize. The regulator contains a proportional (P) and an integral (I) component whose outputs are summarized to a light level output.

The illuminance regulator’s output level only comes into effect if the required output level is higher than the state machine’s output light level. To get full benefit of the regulator, the state machine’s light level output should generally be configured to a lower value than desired, while keeping the target illuminance levels high. This allows the regulator to conserve energy by taking advantage of the room’s ambient lighting.

The regulator operates in a compile time configurable interval between 10 and 100 ms. For each step, the regulator:

  1. Calculates the integral of the error since the last step.

  2. Adds the integral to an internal sum.

  3. Multiplies this sum by an integral coefficient.

  4. Summarizes the sum with the raw difference multiplied by a proportional coefficient.

The error, the regulator coefficients, and the internal sum, are represented as 32-bit floating point values. The resulting output level is represented as an unsigned 16-bit integer.

To reduce noise, the regulator has a configurable accuracy property, which allows it to ignore errors smaller than the configured accuracy (represented as a percentage of the light level). See CONFIG_BT_MESH_LIGHT_CTRL_SRV_REG_ACCURACY and BT_MESH_LIGHT_CTRL_PROP_REG_ACCURACY for more information.

Sensor input

The regulator relies on regular sensor input data to function correctly. This sensor data must come from an external Sensor Server model and report the ambient light level with the bt_mesh_sensor_present_amb_light_level sensor type. The Sensor Server should publish its sensor readings to an address the Light LC Server is subscribed to, using a common application key.

The Light LC Server will process all incoming sensor messages and use them in the next regulator step. The regulator depends on frequent readings from the sensor server to provide a stable output for the Lightness Server. If the sensor reports are too slow, the regulator might oscillate, as it attempts to compensate for outdated feedback.

Tip

Use the Sensor Delta threshold feature for ambient light sensors feeding the regulator. This makes the sensor send frequent reports when the regulator is compensating for large errors, while keeping the mesh traffic low in stable periods.

The Sensor Server may be instantiated on the same mesh node as the Light LC Server, or on a different mesh node in the same area. The regulator performance depends heavily on the sensor’s placement and sensitivity. In general, ambient light sensor devices should be placed in a way that allows their light sensor to capture the human perception of the room’s light level as closely as possible.

Tuning the regulator

Regulator tuning is complex and depends on a lot of internal and external parameters. Varying sensor delay, light output and light change rate may significantly affect the regulator performance and accuracy. To compensate for the external parameters, each regulator component provides user controllable coefficients that change their impact on the output value:

  • Kp - for the proportional component

  • Ki - for the integral component

These coefficients can have individual values for positive and negative errors, referenced as follows in the API:

  • Kpu - proportional up; used when target is higher.

  • Kpd - proportional down; used when target is lower.

  • Kiu - integral up; used when target is higher.

  • Kid - integral down; used when target is lower

Regulators are tuned to fit their environment by changing the coefficients. The coefficient adjustments are typically done by analyzing the system’s step response. The step response is the overall system response to a change in reference value, for instance in a state change in the light level state machine.

Note

The transition time between states in the Light LC Server makes the feedback loop more forgiving. A larger transition time can compensate for poor regulator response.

The illuminance regulator is a PI regulator, which uses the following components to compensate for a mismatch between the reference and the measured level:

  • Instantaneous error - The proportional component that is typically the main source of correction for a PI regulator. It compares the reference value to the most recent feedback value, and attempts to correct the error by eliminating the difference.

  • Accumulated error - The integral component that compensates for errors by adding up the sum of the error over time. Its main contribution is to eliminate system bias and accelerate the system step response.

Changing different coefficients will affect the step response differently. Increasing the two coefficients will have the following effect on the step response:

Coefficient

Rise time

Overshoot

Settling time

Steady-state error

Kp

Faster

Higher

-

-

Ki

Faster

Higher

Longer

Reduced

The value of the coefficients is typically a trade-off between fast response time and system instability:

  • If the value is too high, the system might become unstable, potentially leading to oscillation and loss of control.

  • If the value is too low, the step response might be too slow or unable to reach the target value altogether.

States

Not to be confused with the state machine states, the Light LC Server’s states represent its current mode of operation and configuration.

Mode: bool

Enables or disables the Light LC Server. When disabled, the controlled Lightness Server operates independently.

Occupancy mode: bool

The occupancy mode controls whether sensor activity can turn the lights on. If disabled, motion and occupancy sensor messages may only prevent the lights from turning off, and a light switch is required to turn them on.

Light OnOff: bool

When set, the Light OnOff state may trigger transactions in the lightness state machine. When read, the Light OnOff state indicates whether the lights are turned off (in the Standby state) or on (in the On state or the Prolong state).

Properties

The Light Control Properties are used to configure the Light LC Server behavior. See bt_mesh_light_ctrl_prop for a list of supported properties and their representation.

Extended models

The Light LC Server extends the following models:

Additionally, it requires a Light Lightness Server it can control, instantiated in a different element. See the Composition data structure section for details.

Persistent Storage

If CONFIG_BT_SETTINGS is enabled, the Light LC Server stores all its states persistently using a configurable storage delay to stagger storing. See CONFIG_BT_MESH_MODEL_SRV_STORE_TIMEOUT.

Changes to the configuration properties are stored and restored on power-up, so the compile time configuration is only valid the first time the device powers up, until the configuration is changed.

Power-up behavior

When powering up, the Light LC Server behavior depends on the controlled Lightness Server’s extended Generic Power OnOff Server’s state:

  • On Power Up is BT_MESH_ON_POWER_UP_OFF - The Light LC Server is disabled, and the Lightness Server remains off.

  • On Power Up is BT_MESH_ON_POWER_UP_ON - The Light LC Server is disabled, and the Lightness Server light level is set to its default value.

  • On Power Up is BT_MESH_ON_POWER_UP_RESTORE - The Light LC Server is enabled and takes control of the Lightness Server. If the last known value of the Light OnOff state was On, the Light LC Server triggers a transition to the On state.

Warning

The Light LC Server is only re-enabled on startup if the Lightness Server’s extended Generic Power OnOff Server is in the restore mode.

API documentation

Header file: include/bluetooth/mesh/light_ctrl_srv.h
Source file: subsys/bluetooth/mesh/light_ctrl_srv.c
group bt_mesh_light_ctrl_srv

Light Lightness Control Server model API.

Defines

BT_MESH_LIGHT_CTRL_SRV_INIT(_lightness_srv)

Initialization parameters for Light Lightness Control Server.

Parameters
BT_MESH_MODEL_LIGHT_CTRL_SRV(_srv)

Light Lightness model entry.

Parameters

Enums

enum bt_mesh_light_ctrl_srv_state

Light Lightness Control Server state

Values:

enumerator LIGHT_CTRL_STATE_STANDBY

Standby state

enumerator LIGHT_CTRL_STATE_ON

On state

enumerator LIGHT_CTRL_STATE_PROLONG

Prolong state

enumerator LIGHT_CTRL_STATE_COUNT

The number of states.

Functions

int bt_mesh_light_ctrl_srv_on(struct bt_mesh_light_ctrl_srv *srv)

Turn the light on.

Instructs the controlled Lightness Server to turn the light on. If the light was already on, the dimming timeout is reset. If the light was in the Prolong state, it’s moved back into the On state.

Parameters

  • srv – [in] Light Lightness Control Server instance.

Returns 0

The Light Lightness Control Server was successfully turned on.

Returns -EBUSY

The Light Lightness Control Server is disabled.

int bt_mesh_light_ctrl_srv_off(struct bt_mesh_light_ctrl_srv *srv)

Manually turn the light off.

Instructs the controlled Lightness Server to turn the light off (Standby state). Calling this function temporarily disables occupancy sensor triggering (referred to as “manual mode” in the documentation). The server will remain in manual mode until the manual mode timer expires, see CONFIG_BT_MESH_LIGHT_CTRL_SRV_TIME_MANUAL .

Parameters

  • srv – [in] Light Lightness Control Server instance.

Returns 0

The Light Lightness Control Server was successfully turned off.

Returns -EBUSY

The Light Lightness Control Server is disabled.

int bt_mesh_light_ctrl_srv_enable(struct bt_mesh_light_ctrl_srv *srv)

Enable the Light Lightness Control Server.

The Server must be enabled to take control of the Lightness Server.

Parameters

  • srv – [in] Light Lightness Control Server instance.

Returns 0

The Light Lightness Control Server was successfully enabled.

Returns -EALREADY

The Light Lightness Control Server was already enabled.

int bt_mesh_light_ctrl_srv_disable(struct bt_mesh_light_ctrl_srv *srv)

Disable the Light Lightness Control Server.

The server must be enabled to take control of the Lightness Server. Disabling the server disengages the control over the Lightness Server, which will start running as an independent model.

Parameters

  • srv – [in] Light Lightness Control Server instance.

Returns 0

The Light Lightness Control Server was successfully enabled.

Returns -EALREADY

The Light Lightness Control Server was already enabled.

bool bt_mesh_light_ctrl_srv_is_on(struct bt_mesh_light_ctrl_srv *srv)

Check if the Light Lightness Control Server has turned the light on.

Parameters

  • srv – [in] Light Lightness Control Server instance.

Returns

true if the Lightness Server’s light is on because of its binding with the Light Lightness Control Server, false otherwise.

int bt_mesh_light_ctrl_srv_pub(struct bt_mesh_light_ctrl_srv *srv, struct bt_mesh_msg_ctx *ctx)

Publish the current OnOff state.

Parameters

  • srv – [in] Light Lightness Control Server instance.

  • ctx – [in] Message context, or NULL to publish with the configured parameters.

Returns -EADDRNOTAVAIL

A message context was not provided and publishing is not configured.

Returns -EAGAIN

The device has not been provisioned.

Returns

0 Successfully published the current Light state.

struct bt_mesh_light_ctrl_srv_cfg
#include <light_ctrl_srv.h>

Light Lightness Control Server configuration.

Public Members

uint32_t occupancy_delay

Delay from occupancy detected until light turns on.

uint32_t fade_on

Transition time to On state.

uint32_t on

Time in On state.

uint32_t fade_prolong

Transition time to Prolong state.

uint32_t prolong

Time in Prolong state.

uint32_t fade_standby_auto

Transition time to Standby state (in auto mode).

uint32_t fade_standby_manual

Transition time to Standby state (in manual mode).

uint16_t light[LIGHT_CTRL_STATE_COUNT]

State-wise light levels

struct bt_mesh_light_ctrl_srv_reg_cfg
#include <light_ctrl_srv.h>

Illumination regulator configuration

Public Members

struct sensor_value lux[LIGHT_CTRL_STATE_COUNT]

Target illuminance values

float kiu

Regulator upwards integral coefficient

float kid

Regulator downwards integral coefficient

float kpu

Regulator upwards propotional coefficient

float kpd

Regulator downwards propotional coefficient

uint8_t accuracy

Regulator dead zone (in percent)

struct bt_mesh_light_ctrl_srv_reg
#include <light_ctrl_srv.h>

Illumination regulator

Public Members

struct k_work_delayable timer

Regulator step timer

float i

Internal integral sum.

uint16_t prev

Previous output

struct bt_mesh_light_ctrl_srv_reg_cfg cfg

Regulator configuration

struct bt_mesh_light_ctrl_srv
#include <light_ctrl_srv.h>

Light Lightness Control Server instance.

Should be initialized with BT_MESH_LIGHT_CTRL_SRV_INIT.

Public Members

enum bt_mesh_light_ctrl_srv_state state

Current control state

atomic_t flags

Internal flag field

uint16_t initial_light

Initial light level

struct sensor_value initial_lux

Initial illumination level

uint32_t duration

Fade duration

struct bt_mesh_light_ctrl_srv.[anonymous] fade

Parameters for the start of current state

struct sensor_value ambient_lux

Present ambient illumination

struct k_work_delayable timer

State timer

struct k_work_delayable action_delay

Timer for delayed action

struct bt_mesh_light_ctrl_srv_cfg cfg

Configuration parameters

struct bt_mesh_model_pub pub

Publish parameters

struct bt_mesh_model_pub setup_pub

Setup model publish parameters

struct bt_mesh_lightness_srv *lightness

Lightness server instance

struct bt_mesh_onoff_srv onoff

Extended Generic OnOff server

struct bt_mesh_tid_ctx tid

Transaction ID tracking context

struct bt_mesh_model *model

Composition data server model instance

struct bt_mesh_model *setup_srv

Composition data setup server model instance