A luminary (1) configured for attachment to a ceiling of a space to be illuminated comprises a casing, a fixture for securing a lighting component to the casing, a wireless transmitter module comprising an antenna (10) located in the casing, and a securing component arranged to secure the luminary with respect to a ceiling plate (20). The securing component may be configured to space the casing from the ceiling plate (20) to provide an air-gap (22) between the casing the ceiling plate (20), whereby the casing constitutes a resonant cavity for RF energy transmitted from the antenna (10), the air-gap being dimensioned to radiate RF energy from the antenna (10) to the environment externally of the casing.