Stairwell lighting is typically operated continuously at full output in nonresidential buildings even though these spaces are only intermittently used. In recent years, lighting manufacturers have begun offering a control solution that can reduce energy costs while providing satisfactory levels of illumination for emergency egress. These lighting fixtures automatically adjust light levels based on occupancy.
Click here to read this article I wrote for ELECTRICAL CONTRACTOR about bilevel stairwell lighting.
Update: The article provides general information about stairwell illumination requirements as interpreted by various manufacturers, for educational purposes only. Be sure to check with your local authority about specific requirements applicable in your jurisdiction.