Posted elsewhere and here to show the scientific basis for using UVB flux to control VitD3 photosynthesis in your reptile's skink and to show why UV-Index is not a good measure for reptilian UV response.
My apologies for the high level of the science in the papers cited below , but to get a handle on this one needs to try to get a grip on the science and measured data related to this.
Added here for completeness so it doesn't get buried in the other thread.
Some real physical data from the natural range of pogona species of the UV irradiance in typical summer months (peak of the pogona breeding season in their natural range) that is not supportive of using UV-Index to control pogona UV irradiation and supports higher levels of UVB irradiation ( and UVA too) than advocated some here.
I have several other peer reviewed scientific papers that support my philosophy regarding UV irradiation levels
I started investigating what should be best husbandry practices for the species I've been keeping because of my unease about the disparaty and vagueness of the advise given by self appointed lay experts who have little or no formal scientific training who at best can only to provide anecdotal "evidence" unsupported by hard testable observational measurements that can not reproduced or independently tested in any meaningful way ( somewhat of an issue across the board in this hobby of herpetology).
No small wonder noobs mess up.
Measurements of global spectral irradiance in the UV and visible range were carried out during December 1995 and January 1996 in Townsville, Australia (19.33 degS, 30 m above sea level ) were carried out during December 1995 and January 1996 in Townsville, Australia
using the mobile [scanning] spectroradiometer [provided by the Fraunhofer Institute for Atmospheric Environmental Research].
[ my comment : typical latitude for pogona species , you will note there is no mention of UV-index in this peer reviewed scientific paper ]
The maximum erythemally weighted (UVB) irradiance measured during the campaign was 429 mW/m^2 ( 429 microW / sq.cm) , and the average daily erythemal irradiation for this period was 6.06 kJ/m^2 .
For the year 1991, the December and January values of the monthly mean daily erythemal irradiation found in the survey for Darwin, Brisbane and Perth are as follows:
Darwin, 5.70 kJ/m^2 (December) and 3.72 kJ/m^2 (January)
Brisbane 4.76 kJ/m^2 (December) and 4.47 kJ/m^2 (January)
Perth 5.30 kJ/m^2 (December) and 5.77 kJ/m^2 (January).
The albedo of sand is about 10% in the UV [Blumthalear & Ambach]. According to model calculations UV levels for "desert areas" [dry grasslands and dry woodlands are regarded by these researchers from Germany as "deserts"] should be approximately 3% higher than for forested land.
Source :
Measurements of spectral solar UV irradiance in tropical-Australia.
. Bernhard, B. Mayer, and G. Seckmeyer
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D7, PAGES 8719-8730, APRIL 20, 1997
URL =
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JD00072
Notes
Spectroradiometers are instruments that measure the intensity of radiation as a function of wavelength.
Sampling is generally made at intervals of about 0.5 nm and at relatively high resolution, with full width half intensity (FWHI) less than 1.0 nm.
There are two means by which wavelength sampling is carried out. One uses a single detector and mechanically scans the spectrum across the detector to sample the targeted wavelength range one wavelength at a time.
The second type of instrument uses relatively new array detectors that measure all wavelengths
simultaneously over the targeted spectral range.
Both types of spectroradiometers require careful characterization, and significant effort is required to calibrate the instruments and account for any instrumental dependencies.
The UV index is based on erythemal (HUMAN skin reddening) exposure, since this has the most immediate short-term impact on humans.
It has not been developed nor is relevant to non-human (non- naked mammalian skins ie NOT for reptilian skins or specially evolved skins such that on pogona species , for these there is no model available a.t.m and it is known pogona have evolved the ability to change their skin's IR emissivity and UV albedo at will depending on the temperature and UV irradiance) .
Further
P. vitticeps modify both visible (UV-Vis range) and NIR reflectance to accommodate requirements of signalling or camouflage and thermoregulation during light phases, they are in a rest state during dark phases and have little need to display colour change for other purposes, which may explain their higher proportion of UV-Vis reflectance.
This variation in the proportion of UV reflectance is a function of a change in the spacing of reflecting platelets in iridophores , in combination with melanosome dispersion.
The scales on a reptile act as a barrier for moisture loss , and are highly transparent in UVA & UVB bands.
(OBSERVE MAMMALS (ie humans) DO NOT HAVE THIS ADAPTATION).
Light acts as a stimulus for the pituitary to release MSH, resulting in the dispersion of melanosomes and the aggregation of reflecting platelets. The aggregated reflecting platelets is thus associated with a decrease in the proportion of UV reflectance in relation to NIR reflectance, although the mechanisms moderating NIR reflectance are currently unknown.
I have seen scans of the % UV transmissivity of fish and reptile scales as a function of wavelength created using commonly available scanning UV-Vis spectrophotometers (as found in all chemistry laboratories and even in some high schools).
Some interesting studies on this (unfortunately didn't include pogona species) is here
American Society of Ichthyologists and Herpetologists (ASIH) Copeia Vol. 1959, No. 4, Dec. 30, 1959 pp 311 - 315.
Response to photoperiodic exposure to UV
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4213017/figure/pone-0111504-g003/?report=objectonly
sources
Cyclic Colour Change in the Bearded Dragon Pogona vitticeps under Different Photoperiods.
Marie Fan, Devi Stuart-Fox, and Viviana Cadena
PLoS One. 2014; 9(10): e111504
url
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4213017/
Reptilian Skin and Its Special Histological Structures
Catrin Sian Rutland, Pia Cigler and Valentina Kubale
Veterinary Anatomy and Physiology :
Published: March 13th 2019
url
https://www.intechopen.com/books/veterinary-anatomy-and-physiology/reptilian-skin-and-its-special-histological-structures
VERY BASIC STUFF :
The definition of the UV Index is erythemally weighted global irradiance divided by 25 mW / m^2. (or by 25 microW / sq.cm).
This yields a non-dimensional value that typically can reach a value of 10 under clear-sky conditions at noon for mid-latitude locations during summer. For subtropical and tropical southern hemisphere sites the value can exceed 16.
W/m^2 or mW / cm^2 or microW / cm^2 are the SI units for UV flux (p/unit of area) and the SI unit of irradiation is J/m^2 .
Other dimensionless units are fudges at best since they are at best a poor estimate of erythemal irradiance expressed in an non-standardised unit called the UV-Index as already shown else in the calibration and response curve provided by SolarMeter Corp..
