The first video shows the bot using a photo resistor to detect a light source. If there is no light source detected the bot simply turns in a circle in place. When a light source is detected it follows the light as shown. It's a great, simple way to bring add another component of navigation to the bot.
In the spirt of navigation this version shows the bot with the whiskers still attached and having the bot avoid an object. However, this time to bot will continue to roam, avoiding objects with the whiskers until it finds a bight light source at which time it will stop.