Recent reports from diverse taxonomic groups have made it clear that biofluorescence is widespread in terrestrial vertebrates. It is often presumed that this fluorescent coloration has a visual signalling function, however this hypothesis is not well supported by behavioral experiments or visual models, especially in reptiles and amphibians. The striking glow of these animals under intense UV illumination is misleading, as in natural lighting conditions the low relative proportion of UV wavelengths means that fluorescent emissions will generally be overwhelmed by reflected light and thus not visible. By modelling gecko perception of fluorescent color patches measured with and without sunblock, I show that the fluorescent emissions of the palmatogecko, Pachydactylus rangei, are imperceptible to conspecifics when viewed in daylight. I also describe previously unreported fluorescence from ten species of reptile and one amphibian, primarily from the Namib desert of Namibia and Angola. There is a notable correlation between fluorescent reptile species and desert environments, as well as latitude. Finally, I propose alternative hypotheses for the function of external biofluorescence in reptiles and amphibians, including UV absorbance and light sensing.