Maintenance factor is the ratio of

• A. Lumens on the working plane under normal working conditions to the lumens on the working plane under ideal condition
• B. Lumens on the working plane under ideal working conditions to the lumens on the working plane under normal condition
• C. Lumens falling on the working plane to the lumens emitted by the working plane under ideal condition
• D. Lumens emitting by the working plane to the lumens falling on the working plane under ideal condition