A lighting device for a respiratory humidifier (1) is provided, the humidifier comprising a liquid container (3) with a bottom plate and a housing (2) with a heating plate (8), wherein the heating plate (8) can be heated for heating the liquid in the liquid container (3), and wherein the bottom plate can be brought into contact with the heating plate (8), wherein the housing (2) comprises a light source (20) and a light exit portion (22), and the liquid container (3) comprises a light entrance portion (21), wherein the light proceeding from the light source (20) proceeds in a lighting direction through the light exit portion (22) and the light entrance portion (21) and thus arrives in the liquid container (3).
