Lite-On Ambient Light & Proximity Sensors


LTR-329 and LTR-303 Ambient Light Sensors.


LTR-303 Sensor in Home Assistant UI.

The ltr_als_ps sensor platform allows you to use a range of LiteOn ambient light and proximity sensors with ESPHome. The I²C Bus is required to be set up in your configuration for this sensor to work.

The family of sensors includes:

  • Ambient Light Sensors LTR-303ALS and LTR-329ALS

  • Integrated Ambient Light and Proximity Sensors LTR-553ALS, LTR-556ALS, LTR-559ALS

  • Proximity Sensor LTR-659ALS (with PS gain control)

The sensors are very similar and share the same datasheet. First two have default I²C address 0x29 and the rest have default I²C address 0x23. The sensors are available on breakout boards from a number of vendors, for example Adafruit or Pimoroni.

Proximity sensors are the same sort of sensors that you find in phones and tablets to disable the screen when you hold the device up to your ear. They might be useful for automated turning on or off of displays and control panels. An example is the CoreS3 board from M5Stack that has an LTR-559ALS sensor integrated just under the screen.

Ambient light sensing

The sensor platform provides a linear response over a wide dynamic range from 0.01 lux to 64k lux and is well suited to applications under high ambient brightness. There are altogether six gain settings (1X, 2X, 4X, 8X, 48X and 96X) available for user to configure. Use higher gain for dimmer areas.

The devices consist of two photodiodes: The CH0 diode is sensitive to both visible and infrared light and the CH1 diode is sensitive only to infrared light.


CH0 and CH1 typical spectral response

Ambient light illuminance calculation

Excerpt from the datasheet:

IF (RATIO < 0.45)
    ALS_LUX = (1.7743 * CH0 + 1.1059 * CH1) / ALS_GAIN / ALS_INT
ELSEIF (RATIO < 0.64 && RATIO >= 0.45)
    ALS_LUX = (4.2785 * CH0 – 1.9548 * CH1) / ALS_GAIN / ALS_INT
ELSEIF (RATIO < 0.85 && RATIO >= 0.64)
    ALS_LUX = (0.5926 * CH0 + 0.1185 * CH1) / ALS_GAIN / ALS_INT
    ALS_LUX = 0


  • CH0 and CH1 are the sensor values (measurement counts) for Visible + IR (Ch0) and IR only (Ch1) sensors respectively.

  • ALS_GAIN is the gain multiplier

  • ALS_INT is the integration time in ms/100

ALS Gain levels

The table lists gain values and corresponding illuminance range:


Illuminance range


1 lux to 64k lux (default)


0.5 lux to 32k lux


0.25 lux to 16k lux


0.125 lux to 8k lux


0.02 lux to 1.3k lux


0.01 lux to 600 lux

This Wikipedia article has a table of some lux values for comparison.

Proximity sensing

The proximity sensor has a built-in emitter and detector. The sensor detects reflected IR light from the emitter and gives a raw count value inversely exponential to the distance. A decrease in the count value means an object is getting further away from the sensor, and vice-versa. Neither of the datasheets provides any information on how to convert the raw count value to distance. The only way to do it is to test the sensor yourself and select the threshold according to your needs and environment. Exact numbers will depend on the type of the object, its color and reflectivity.

Example configuration

  - platform: ltr_als_ps
    address: 0x23
    update_interval: 60s
    type: ALS_PS  # or ALS or PS
    ambient_light: "Ambient light"
    # PS only section
    ps_cooldown: 5 s
    ps_high_threshold: 500
        - .... # do something - light up the screen for example
    ps_counts: "Proximity counts"

Configuration variables:

  • id (Optional, ID): Manually specify the ID used for code generation.

  • address (Optional, int): Manually specify the I²C address of the sensor. Default is 0x29.

  • type (Optional, string): The type of the sensor. Valid values are ALS_PS (default) for integrated sensors, ALS for ambient light only or PS for proximity only devices.

  • auto_mode (Optional, boolean): Automatic gain and integration time selection. Defaults to True.

  • gain (Optional, string): The gain the device will use. Higher values are better in low-light conditions. Valid values are 1X (default), 2X, 4X, 8X, 48X, 96X.

  • integration_time (Optional, Time): The amount of time sensors are exposed. Longer means more accurate values. Valid values are: 50ms (default), 100ms, 150ms, 200ms, 250ms, 300ms, 350ms, 400ms.

  • glass_attenuation_factor (Optional, float): The attenuation factor of glass if it’s behind some glass or plastic facia. Default is 1.0 means 100% transmissivity. 2 means 50% transmissivity etc.

  • update_interval (Optional, Time): The interval for checking the sensors. Defaults to 60s.

  • ps_cooldown (Optional, Time): The “cooldown” period after the proximity sensor is triggered. Helps to avoid multiple calls. Defaults to 5s.

  • ps_gain (Optional, string): The gain the device will use for proximity sensor. Higher values are better in low-light conditions. Valid values are 16X (default), 32X, 64X. Only for LTR-659ALS.

  • ps_high_threshold (Optional, int): The threshold for the proximity sensor to trigger on object getting closer. Defaults to 65535, which implies it will never be triggered.

  • ps_low_threshold (Optional, int): The threshold for the proximity sensor to trigger on object getting further away. Defaults to 0, which implies it will never be triggered.

  • on_ps_high_threshold (Optional): Actions to perform when the proximity sensor is triggered on object getting closer.

  • on_ps_low_threshold (Optional): Actions to perform when the proximity sensor is triggered on object getting further away.


This component offers five sensors for ALS-equipped devices and one sensor for PS-equipped devices. You can configure all or any subset of these sensors. Each configured sensor is reported separately on each update_interval. Each is an ESPHome sensor and may be configured accordingly; if you don’t need to configure additional sensor variables, you may simply use the shorthand syntax for the sensor. For example: ambient_light: "Ambient light"

  • ambient_light (Optional): Illuminance of ambient light, close to human eye spectre, lx.

  • infrared_counts (Optional): Sensor counts from the IR-sensitive sensor (CH1), counts.

  • full_spectrum_counts (Optional): Sensor counts from the sensor sensitive to both visible light and IR (CH0), counts.

  • actual_gain (Optional): Gain value used to measure data, multiplier. Particularly useful when “auto_mode” is selected.

  • actual_integration_time (Optional): Integration time used to measure data, ms. Particularly useful when “auto_mode” is selected.

  • ps_counts (Optional) - Raw 11-bit reading from proximity sensor, counts.

See Also