UVB Coverage Calculator

This calculator applies the inverse-square law that governs how UVB intensity falls off with distance -- doubling the distance from a bulb cuts UV Index to roughly a quarter -- to work backward from your species' Ferguson Zone UV requirement to an Optimal Distance for bulb placement. Ferguson Zone is the input that moves the target UV Index the most: it spans a roughly ten-fold range from Zone 1 shade-dwellers (UVI 0-0.7) to Zone 4 mid-day baskers (UVI 2.6-3.5), directly setting how intense the UVB needs to be at the basking spot. Bulb Type sets the starting UVB output at a reference distance and also determines Replace After (months), since T8 bulbs degrade fastest and mercury vapor bulbs land in between, while T5 HO bulbs hold their output longest. Mesh Screen, when toggled on, attenuates UVB output by roughly 35% to account for the screen material blocking part of the UV spectrum, pushing the bulb closer to compensate.

Enclosure Length does not affect Optimal Distance at all -- distance is set purely by the bulb's output and the target UVI -- but it does set the Recommended Bulb Length, aiming to cover roughly two-thirds of the enclosure so the animal has both a UVB gradient and shaded retreat areas. Coverage Area is calculated differently depending on bulb shape: for the linear T8 and T5 HO bulbs, it's a simple geometric footprint under the Recommended Bulb Length (the full length by half that as width), so it does not vary with Bulb Type, Ferguson Zone, or Mesh Screen -- it is not an intensity-based figure for those three bulb types. Mercury vapor, being a spot lamp rather than a linear tube, gets a coverage diameter derived from Optimal Distance instead, so its Coverage Area does reflect bulb output, zone target, and mesh attenuation. The zone targets themselves follow the published Ferguson Zone system -- Baines et al.'s 2016 "UV-Tool" paper in the Journal of Zoo and Aquarium Research, which assigns species to one of four UV Index exposure zones based on field measurements of wild reptile basking behavior -- combined with typical manufacturer UVB output data, but real bulb output varies by manufacturer and individual unit, so a UV meter reading at the actual basking spot is the only way to confirm real-world UVI.