How do you unlock the good ending in Metro 2033

To achieve the 'Good Ending' in Metro 2033, the player must earn a certain amount of good karma points. There is a large amount of options that allows the player to get good karma, but only a few are needed to allow the good ending.

The screen will flash a yellowish colour and a whispering voice is heard when the player does something that earns good karma.

Examples of good karma throughout the game include, completing certain levels without killing any enemies, giving military-grade bullets (The game's currency) to those in need, eavesdropping on conversations between enemy soldiers, etc.

The good ending allows the player to shot and knock off the laser designator before it locks onto the Dark One's lair. The player can unlock the good ending and not choose to shot the laser designator and therefore end the game with the 'bad ending'.