Here is a great project if you want to learn about external sensors within the Arduino-sphere. Maker Pro user Reginald Watson has put together a tutorial on controlling an LED light strip with hand gestures.
Aside from an Arduino, the APDS-9660 RGB and gesture sensor is at the heart of this project. It's a tiny breakout board that can measure ambient light, proximity, colour and touchless gestures. This is the same sensor that was used in the Samsung Galaxy S5 to reduce screen brightness based on the ambient light and to disable the touchscreen when on a call. It's not only one of the best sensors on the market right now, it's also one of the cheapest.
Reginald uses the WS2812B LED strip which has 5050 RGB LEDs and integrated drivers that allow each LED to be addressable which can produce complex effects with only a few lines of code.
Putting it all together is a breeze, making it a great project for beginners who want to explore the Arduino world.
Your final product leaves you with an LED strip that can change colour, create patterns or adjust it's brightness with a simple wave of your hand.
Everything you need to get started including step by step instructions and all of the code you will need is available here.