Nightingale Armor

The Nightingale Armor is set of Light Armor given to the Dragonborn and Brynjolf by Karliah before performing the initiation ritual of the Nightingales during the Trinity Restored quest for the Thieves Guild. All of the armor pieces are obtained from a box with the Nightingales symbol emblazoned on it. It is possible to pickpocket the armor back from Karliah if the player has the applicable perk.When looking closely in 3rd person mode, the DragonBorn's eyes glow white, as do other characters with the armor.

The armor container in the developers' room (accessible on PC only, the command is coc qasmoke) contains three sets of Nightingale Armor with varying armor ratings and enchantment strengths. The BaseIDs given are of the middle set.

Magic effects
Wearing all four pieces of Nightingale Armor grants the effect "Nightingale Armor Full Set" which increases armor rating by 25 points. This bonus applies after the perks Custom Fit and Matching Set.

Improvement
Nightingale armor can be improved using void salts. There are six levels of improvement Fine, Superior, Exquisite, Flawless, Epic and Legendary. When combined with a high light armor skill and perks, a high smithing skill, fortify smithing potions and enchanted smithing apparel this can easily exceed 567 armor rating, (or 80% damage reduction).

Attributes
The armor's value and enchantments are dependent on the player's level when the mission: Trinity Restored is started - not when the armor is received.

Bugs

 * If the armor is worn on a Khajiit or an Argonian, the tail will slip through the cape.
 * Sometimes, Nightingale armor can't be upgraded even when you have a sufficient smithing skill, smithing perks and void salts. (This could possibly be a result of the player having the fine-cut void salts in their inventory, turning them in to captain of the ship in Dawnstar should fix the bug)
 * Sometimes the coloring of the Hood will go and it will become white (PS3 confirmed (as well as Nightingale hoods worn by others), 360 confirmed but only when equipping in shadows, others need confirmation). Reinstalling the game seems to fix this. Turning the console off and then back on appears to work on PS3. Another way to fix this is to drop it on the ground during the day time and wait until night, pick it back up and equip it.
 * While wearing the gloves, human fingers skin tone will always look the same no matter your character's skin tone.
 * There is a bug when you try to retrieve the armor this way, when you click the stone nothing happens.
 * Argonian and Khajiit faces are shortened when wearing the hood and look like normal human head models.
 * If the player obtains all smithing perks except for the last optional one, the Nightingale armor will only upgrade to flawless. (Getting the last perk seems to fix this)
 * 'Giving' the armor to one of the armor mannequins in Proudspire Manor, then removing it, will sometimes result in a duplication of some of the pieces of the set (confirmed on multiple PC playthroughs; confirmed on PS3)
 * It's possible to use mannequins in Proudspire Manor to duplicate all pieces of the set on Xbox360. This only seems to work with the mannequin on the right. (the mannequin on the left seems to not register the hood)
 * When given to a follower who has heavy starting armor, you may not be able to get it back because it's "Your followers starting armor." The only way to get it back from your follower is to kill them and loot it back.
 * To upgrade the set past flawless, you need enchanted smithing items/smithing potions and 100 smithing. This may depend on what level you are when you obtain the set. (Level 20+ requires 100 smithing+enchanted items)
 * Replacing the Nightingale Hood with a Shrouded Hood still gives the set effect.
 * Can be duplicated in the Dawnstar Sanctuary after buying the master bedroom upgrade from Devlin. Place the armor you want duplicated into the inventory of the mannequin then take it back again (without leaving the inventory menu). leave the area. Come back and the duplicated armor should be there (minus any improvements you have put unto it. Also works in the house Honeyside and in house Vlindrel Hall

Trivia

 * Nightingale Armor is unique as it is the only type of apparel, other than Ulfric's Clothes in the game to come with a cape.