An aircraft cabin lighting system comprises one or more cabin lighting units, each cabin lighting unit comprising an emergency exit sign arranged to be electrically illuminated; and one or more luminescent emergency exit signs. The luminescent emergency exit signs are portable, and each comprise an adhesive layer arranged to allow the luminescent emergency exit sign to be adhered to a surface. The signs are arranged to be adhered to a surface in the vicinity of the electrical emergency exit sign in use, and do not require electricity to function.