LightenUp: free puzzle app game for iphone, ipad

LightenUp is a free puzzle app from Dariusz Morawiec. No idea how to pronounce his name.

Look at the first image to get the rules.

 The first 40 puzzles are free. They are the size of the 2nd image.  I did them in about 15 minutes. The small grid sizes are perfect for people new to the genre.

The next 100 puzzles you have to pay for. They're bigger.

I've been doing this type of puzzle for years. Another name is Lighthouses. The best version is Akari 3D which takes this concept to a cube mode.