An optical construction (100) includes a lightguide (102), a transmissive reflector (112), and an optical sensor (114). The lightguide (102) includes a first major surface (104) and a second major surface (106) opposite to the first major surface (104). The first major surface (104) includes a first portion (108) and an adjoining second portion (110). The transmissive reflector (112) is disposed adjacent to the first major surface (104) of the lightguide (102). The optical sensor (114) is disposed adjacent to the transmissive reflector (112) opposite to the lightguide (102). The optical sensor (114) is aligned with the first portion (108) of the first major surface (104) of the lightguide (102), such that the optical sensor (114) receives at least a portion of light passing through the first portion (108) of the first major surface (104) and transmitted by the transmissive reflector (112). The optical construction (100) further includes an enclosed gap (116) disposed between the first portion (108) of the first major surface (104) of the lightguide (102) and the transmissive reflector (112).