Thanks for the replies. According to a FB reptile group, who tested meters at all price ranges, the sensor and filter restricts how low the price can go, and that seems to be the Solar Meter 6.5, as Charon mentioned, at about £200. Given that overexposure can cause real harm, that would seem to be the minimum. It is possible to just use the distance recommended by the bulb maker for each type and and species, but my birds aren't captive, being free flying in the house in the day. Usually, you would set the bulb above the cage and run the bulb to give a set daily dose to the caged birds. My intention is to make a perching area outside the cages with a mix of daylight and uv tubes above the perch (mine are 2ft T5's). The UV light will be on for a sufficient period that they need, depending on how often/how long they sit on that perch. The daylight bulbs will stay on continuously in the day. I need the meter to get an idea of the dosage at given distances because of their free movement and potential proximity to the light. Picture a uv tube in between one or two daylight tubes hanging above the perch on top of a cage with a simple wood frame for the lights to hang together. I have 6 budgies.