DELL offers backlit keyboard in its Laptop/Notebook which is an optional feature. But unlike Apple MacBook Pro, there is no sensor which can automatically turn on backlit keyboard in dim light. Instead, you need to manually enable the backlit keyboard if you have it on your device. See how to do that -
To Turn On Backlit Keyboard in Dell laptops like Studio/Vostro/XPS/Latitude, “Hold the Fn key and press the Right Arrow key”. You can see all symbols illuminating on the keys. With the same hotkey you can toggle between the three lighting states (in the given order). The lighting modes are: full keyboard, half keyboard & off.
Note: This only works if you have purchased the optional backlit keyboard while ordering. Studio Laptops with backlit keyboard have an additional icon for the LED on/off switch, which is located on the right arrow key.