What are orbs of light

I'll convert my comment to an answer as it was getting long.

I get the feeling playing the game that precision kills drop more ammo, but have no evidence.

Do be aware some guns have the 'surplus' attribute which means more ammo will be found for that weapon slot.

Thanks to @Havatra for the thought. There might indeed be Grimoire cards for this. Here is an example of an area bonus earned through killing enemies in that area. So far I have seen bonuses to, EXP, Weapon EXP and Materials, but I don't have a huge Grimoire score and http://destiny-grimoire.info/ doesn't have the card bonuses listed.

If you fully level up a legendary weapon without actually purchasing the upgrades you will get twice the amount of Ascendant Energy. You DO NOT need to spend a single glimmer or material on the item.

Basically instead of getting 2-3 you will get 4-6 or something like that. Good if all your weapons are already fully leveled, you can switch weapons before you hand in a bounty.

However this does not work for armour.