Redfoot tortoises in the shade, do they need UVB?

A common question from new Redfoot tortoises is "Why do I need a UVB light. Don't Redfoot tortoises live in the shade?"

Aside from the fact that they aren't strict deep forest dwellers, the following shows that they do get UVB even in deep shade. Here in South Carolina I have confirmed this using a Solarmeter 6.2 UVB radiometer.

Excerpts  from: 
DIFFUSE COMPONENT OF THE SOLAR ULTRAVIOLET RADIATION IN TREE SHADE 
A.V. Parisi, M.G. Kimlin, J.C.F. Wong, M. Wilson Centre for Astronomy and Atmospheric Research, University of Southern Queensland, Toowoomba, 4350, Australia.

J Photochem Photobiol B. 2000 Feb;54(2-3):116-20.

Comments added by me are in red italics.

INTRODUCTION

CONCLUSIONS

*UV Erythemal action spectrum for humans has been employed widely for assessing the UV effect on human skin. The value of the sensitivity is normalized to unity at 298 nm (the UVB wavelength also most efficient for Vitamin D3 synthesis).

The whole paper can be viewed here

But there is more !!

Photochemistry and Photobiology 78(2):180-183. 2003
doi: 10.1562/0031-8655(2003)078<0180:SUBPSS>2.0.CO;2

Scattered UV Beneath Public Shade Structures During Winter

D. J. Turnbull*, A. V. Parisi, J. Sabburg

Centre for Astronomy, Solar Radiation and Climate, University of Southern Queensland, Toowoomba, QLD, Australia

102*To whom correspondence should be addressed at: Centre for Astronomy, Solar Radiation and Climate, University of Southern Queensland, Toowoomba 4350, QLD, Australia. Fax: +61-7-46311530;

Abstract

Broadband field measurements were conducted beneath three different-sized public shade structures, small, medium and large, during winter in the Southern Hemisphere. These measurements were compared with the diffuse UV to quantify the relationship of the UV under and around the shade structures to the diffuse UV. For the shade structures, a relationship between the diffuse UV and the UV in the shade has been provided for clear skies and solar zenith angles (SZA) of 49–76°. This allows the prediction of the UV in the shade of these structures if the diffuse UV is known. The ultraviolet protection factors for the three shade structures ranged from 1.5 to 5.4 for decreasing SZA. For the greater SZA of 70–76°, the erythemal UV in the shade was 65%, 59% and 51% of that in full sun for the small, medium and large structures, respectively. For the smaller SZA of 50–53° the erythemal UV in the shade was 35%, 41% and 18% for the small, medium and large shade structures, respectively. From this research it can be concluded that the UV radiation levels in the shade in winter could cause erythema and other sun-related disorders.