Pair of IR sensors have sender and receiver sensors but some one declares it is possible to use this sensors for lighting stair case however I have used them for automatic liquid dropper and hand dryer and soap dispensers to control a motor.
lighting a staircase directly by IR light would not be very effective for usage by human beings...
But when using the 'IR sender and receiver sensor' as a light barrier*), which is able to trigger a lighting unit for visible light, you are can indirectly use it for ilighting a staircase.
But I may have misinterpreted your question...
*) as in the case of your liquid drooper and the hand dryer