Optical construction

An optical construction comprising:

• a lightguide comprising a first major surface and a second major surface opposite to the first major surface, the first major surface of the lightguide comprising a first portion and an adjoining second portion;
• a transmissive reflector disposed adjacent to the first major surface of the lightguide, wherein the transmissive reflector substantially reflects light in a first wavelength range and substantially transmits light in a second wavelength range;
• an optical sensor disposed adjacent to the transmissive reflector opposite to the lightguide, wherein the optical sensor is aligned with the first portion of the first major surface of the lightguide, such that the optical sensor receives at least a portion of light passing through the first portion of the first major surface and transmitted by the transmissive reflector;
• and
• an enclosed gap disposed between the first portion of the first major surface of the lightguide and the transmissive reflector, such that light received by the optical sensor passes through the enclosed gap, wherein the lightguide further comprises a plurality of protrusions disposed on the first major surface of the lightguide, at least some of the protrusions engaging the transmissive reflector, wherein an average thickness of the protrusions disposed on the first portion of the first major surface is less than the average thickness of the adjoining protrusions disposed on the second portion of the first major surface, such that the enclosed gap is provided between the first portion and the transmissive reflector.