Rare luxuries use 10, and typically grant a % bonus, making them ideal for late-game systems with many existing boosts from System Improvements. Uncommon luxuries use 20, and typically grant a bonus per Population, making them ideal for older, filled-out systems. Common luxuries use 40, and typically grant a large flat bonus to the system, making them ideal for newer systems. When used for system development, the number of luxuries used, and their typical effect, is based on what tier the luxury is: Common luxuries are available at the start of the game, whereas Uncommon and Rare luxuries are revealed upon reaching Tier 3 and Tier 4 of the Science and Exploration tree, respectively. There are three tiers of luxury resources. They provide passive bonuses to the planet they are found on, can be spent on system development, boost population growth, and can be involved when dealing with minor factions. Luxury resources are a type of resource that can be found on planets or acquired through trade.