In this part of the lesson, you will add a light sensor to your virtual IoT device.
## Virtual Hardware
The nightlight needs one sensor, created in the CounterFit app.
The sensor is a **light sensor**. In a physical IoT device, it would be a [photodiode](https://wikipedia.org/wiki/Photodiode) that converts light to an electrical signal. Light sensors are analog sensors that sends an integer value indicating a relative amount of light, that doesn't map to any standard unit of measurement such as [lux](https://wikipedia.org/wiki/Lux).
### Add the sensors to CounterFit
To use a virtual light sensor, you need to add it to the CounterFit app
1. Open the nightlight project in VS Code that you created in the previous part of this assignment. Kill and re-create the terminal to ensure it is running using the virtual environment if necessary.
1. Open the `app.py` file
1. Add the following code to the top of `app.py` file with the rest of the `import` statements to connect to import some required libraries:
```python
import time
from counterfit_shims_grove.grove_light_sensor_v1_2 import GroveLightSensor
```
The `import time` statement imports the Python `time` module that will be used later in this assignment.
The `from counterfit_shims_grove.grove_light_sensor_v1_2 import GroveLightSensor` statement imports the `GroveLightSensor` from the CounterFit Grove shim Python libraries. This library has code to interact with a light sensor created in the CounterFit app.
1. Add the following code to the bottom of the file to create instances of classes that manage the light sensor:
```python
light_sensor = GroveLightSensor(0)
```
The line `light_sensor = GroveLightSensor(0)` creates an instance of the `GroveLightSensor` class connecting to pin **0** - the CounterFit Grove pin that the light sensor is connected to.
1. Add an infinite loop after the code above to poll the light sensor value and print it to the console:
```python
while True:
light = light_sensor.light
print('Light level:', light)
```
This will read the current light level using the `light` property of the `GroveLightSensor` class. This property reads the analog value from the pin. This value is then printed to the console.
1. Add a small sleep of one second at the end of the `while` loop as the light levels don't need to be checked continuously. A sleep reduces the power consumption of the device.
```python
time.sleep(1)
```
1. From the VS Code Terminal, run the following to run your Python app:
1. From the CounterFit app, change the value of the light sensor that will be read by the app. You can do this in one of two ways:
* Enter a number in the *Value* box for the light sensor, then select the **Set** button. The number you enter will be the value returned by the sensor.
* Check the *Random* checkbox, and enter a *Min* and *Max* value, then select the **Set** button. Every time the sensor reads a value, it will read a random number between *Min* and *Max*.
