Turtle Uvbintensity Calculator
Calculate turtle uvbintensity with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
UVB = Baseline x (12/Distance)^2 x MeshFactor x DegradationFactor
UVB intensity follows the inverse square law. The baseline output at 12 inches is adjusted by the square of the distance ratio. Mesh screens reduce output by ~35%. Bulb degradation follows exponential decay with a half-life of 6-12 months depending on bulb type. The result is compared against Ferguson Zone thresholds for suitability.
Worked Examples
Example 1: T5 HO Setup for Red-Eared Slider
Problem:A 24W T5 HO bulb is mounted 12 inches above the basking spot, through a mesh screen. The bulb is 4 months old. Is the UVB adequate?
Solution:Base UVB at 12 inches: 80 uW/cm2\nDistance factor: (12/12)^2 = 1.0, so 80 uW/cm2\nMesh reduction: 80 x 0.65 = 52 uW/cm2\nAge degradation (4 months, 12-month half-life): factor = 0.5^(4/12) = 0.794\nCurrent UVB: 52 x 0.794 = 41.3 uW/cm2\nFerguson Zone 2 — too low for aquatic turtles
Result:UVB: ~41 uW/cm2 (Zone 2). Insufficient. Remove mesh or move bulb to 8 inches.
Example 2: Mercury Vapor Bulb for Tortoise
Problem:A 160W mercury vapor bulb is 18 inches from the basking spot, no mesh, brand new. Is it adequate for a tortoise (Zone 4)?
Solution:Base UVB at 12 inches: 130 uW/cm2\nDistance factor: (12/18)^2 = 0.444\nUVB at 18 inches: 130 x 0.444 = 57.8 uW/cm2\nNo mesh, no age degradation\nFerguson Zone 2 — too low for a tortoise at this distance
Result:UVB: ~58 uW/cm2 (Zone 2). Move bulb to 12 inches for Zone 4 output (~130 uW/cm2).
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy