The A380's upper and lower decks are connected by two stairways, one fore and one aft, with both being wide enough to accommodate two passengers side by side; this cabin arrangement allows multiple seat configurations. The maximum certified carrying capacity is 853 passengers in an all-economy-class layout, Airbus lists the "typical" three-class layout as accommodating 525 passengers, with 10 first, 76 business, and 439 economy class seats. Airline configurations range from Korean Air's 407 passengers to Emirates' two-class 615 seats and average around 480–490 seats. The Air Austral's proposed 840 passenger layout has not come to fruition. The A380's interior illumination system uses bulbless LEDs in the cabin, cockpit, and cargo decks. The LEDs in the cabin can be altered to create an ambience simulating daylight, night, or intermediate levels. On the outside of the aircraft, HID lighting is used for brighter illumination.