A portable environmental monitoring instrument comprising: a housing comprising a main body and a cap; a display mounted to the housing; a processing circuit disposed within the main body, the processing circuit electrically connected to the display; a light sensor mounted to the housing and electrically connected to the processing circuit; a humidity sensor electrically connected to the processing circuit; and a probe member extending from the main body and exposed to the environment by opening the cap, the probe member carrying a temperature sensor at a distal end thereof and part of an electrical connection between the temperature sensor and the processing circuit, the processing circuit arranged to process signals received from the light sensor, the humidity sensor and the temperature sensor to obtain an environmental measure indicative of the affect of the environment and control the display to display data indicative of the environmental measure.