> For the complete documentation index, see [llms.txt](https://iot.datalit.de/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://iot.datalit.de/2-internet-of-things/iot-in-our-apps/program-the-devices/sensors/ambient-light-sensor.md).

# Ambient Light Sensor

## Goals

{% hint style="success" %}

* You know how to get a handle on the ambient light sensor connected to your computer
* You can get the sensor's values and get frequently notified about new values
  {% endhint %}

## Get the ambient light sensor and subscribe to updates

Working with an [Ambient Light 2.0](https://www.tinkerforge.com/en/doc/Hardware/Bricklets/Ambient_Light_V2.html) sensor works as described in the general article on [how to use sensors](/2-internet-of-things/iot-in-our-apps/program-the-devices/sensors.md). In this article, we assume you have successfully initialized the devices with the [Tinkerforge Device Manager](/2-internet-of-things/iot-in-our-apps/connect-to-devices/the-tinkerforge-device-manager.md), and you stored all connected devices on a global variable `devices`. We also declared a global variable called `ambientLightSensor`. 

Next, we need to know the device identifier, which **259**:

```javascript
// Get the ambient light sensor via its device identifer
ambientLightSensor = devices.getDeviceByIdentifier(259);
```

Once we have a reference to the sensor, we can register a callback function:

```javascript
// We want to be informed when a new sensor value arrives
ambientLightSensor.registerListener(ambientLightChanged);
```

Of course, we have to actually define the function:

```javascript
function ambientLightChanged(val) {
   // Do something with the value object
}
```

## Reading the light value

The sensor delivers only one value, which we can access via the `val` object. The value is the light intensity measured in Lux multiplied by 100:

```javascript
function ambientLightChanged(val) {
    // Get the value
    var value = val.getValue();
    log(value.value / 100.0 + " lx");
}
```