Howdy All,
I got permission from Deena to forward on her email about another UVB study doen in Finland. I'll just say this; it brings out something that I had never heard about, in that UVB from the wrong wavelength effectively cancels out the good effects of UVB in the proper D3 conversion band. The long story short, the ZooMed Reptisun 5.0 actually had the best D3 conversion factor of the 14 bulbs tested! Deena summarizes the article and lists a few of the more common lamps that were tested. If anyone has access to the full article and can add more info, by all means do so! So here goes...
Dave Weldon
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I wanted to share this information from an article that appeared in
the Bulletin of the Chicago Herpetological Society (Vol. 40, Number
1, Jan. 05). The article is fairly long (7 pages + 2 additional
pages of graphs) and I don't want to violate copyright laws by
scanning and posting it, but I'll try very hard to give you a decent
summary. It's pretty technical, so I'll try my best. I found this
article to be very interesting. I am posting this to both the AIML
and the UVB_Meter_Owners group, so my apologies if you see this
twice.
Deena
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Article Title: UV-lamps for Terrariums: Their Spectral
Characteristics and Efficiency in Promoting Vitamin D3 Synthesis by
UVB Irradiation
Author: Jukka Lindgren
Originally published by the Herpetological Society of Finland
[Herpetomania 13(3-4), 2004]
Abstract: Sufficient irradiation within a narrow sub-band of the UVB
range is a prerequisite for the photosynthesis of vitamin D3 in
skin. Although radiation below wavelength of 300 nm promotes
photosynthesis of vitamin D3, radiation above 300 nm destroys
vitamin D3 that has been already synthesized in skin tissue or
nutritionally obtained. Furthermore, skin temperature has a
significant effect on the pace of vitamin D3 synthesis. In a
terrarium, the required UVB-radiation has to be artificially
produced with dedicated lamps. In the study, the characteristics of
light produced by fourteen different models of UV and full spectrum
lamps specifically designed for terrarium use were measured over a
range of 250-800 nm. As a reference, the spectrum of natural
sunlight was also measured when the sun was at its highest point of
elevation in the southern sky of Finland. The proportion of
radiation energy that takes part in the photosynthesis of vitamin D3
was determined and the D3 Yield Index was calculated. Significant
differences as large as a thousandfold were found in the D3 Yield
Indices. The resulting conclusion is that UVB radiation as a
percent of the total radiation figure does not necessarily give a
true indication of a lamp's capability to maintain cutaneous
production of vitamin D3.
Explanation of study:
1) Fourteen lamps of various makes and models were obtained for the
study. The lamps included the following: a new Reptisun 5.0 14W
(ZooMed), a 10-month old Reptisun 5.0 15W, Reptistar 30W (Sylvania),
Reptilight 36W(Narva), Repti Glo 40W, Life-Glo 40W, and Exo-Terra
Repti-Glo 40W 2.0, 5.0 and 8.0 - all by Rolf C. Hagan Corp., ESU
Reptile Super UV Daylight 40 W, ESU Reptile Desert 7% UV 40W, Active
UVHeat 100W (Wild Inside), True-Light 36W and True-light Daylight
6000 15 W ("Manufactured for AD-Lux Oy"). Other "full-spectrum"
bulbs not designed for UV output were also included, but I won't
list them here.
2) Measurements were taken of UVA, UVB and UVC emitted by each
lamp. "Measurements were made by Suomen Aurinkosimulaattori
Oy/Solar Simulator Finland Ltd. The spectroradiometer used for all
measurements was IL700A Research Radiometer, by International Light
Inc."
3) UVB irradiance was divided into two categories - what the author
calls UVB-1 and UVB-2. UVB-1 values represent UVB emitted in the
wavelengths range that mainly contributes to vitamin D3
photosynthesis (280-304nm) while UVB-2 values represent UVB emitted
in the wavelengths that may potential destroy vitamin D3 (305-319
nm). The author explains that "the ability of a lamp to efficiently
produce vitamin D3 can be evaluated by comparing values in table 3
[UVB-1 and UVB-2 values]. The higher the irradiance of UVB-2 is in
comparison to UVB-1, the higher the probability that UVB-2 radiation
will start destroying cutaneous vitamin D3."
4) The D3 Yield Index for each bulb was calculated. The author
explains D3 Yield Index: "The basis for the calculation of the D3
Yield Index was the action spectrum of 7-DHC to pre-D3 conversion in
human skin. The index was calculated in the 252-313 nm range by
weighing the irradiance at each wavelength in accordance with the
action spectrum. The effective irradiances thus obtained were
summed over this range, and this value was finally adjusted to the
reference by a suitable multiplication factor, resulting in the
final D3 Yield Index."
He continues, "Use of the D3 Yield Index as a basis for evaluation
of UV lamps gives a possibility to compare very different types of
lamps with consistent criteria. The D3 Yield Index turns the
attributes of a spectrum curve, that are otherwise difficult to
compare, into an easily manageable and understandable form even for
the novice keeper; they indicate with an unambiguous value the
efficience of a lamp to promote photosynthesis of vitamin D3 and by
that, indirectly ensure sufficient level of calcium metabolism."
Results:
Here are some of the data on the lamps. To shorten the amount of
typing I have to do and the amount of reading you have to do, I'll
just include the lamps most commonly purchased and discussed by
hobbyists.
New Reptisun 5.0
UVB-1: 2.057
UVB-2: 8.232
D3 Yield Index (YI): 439.3
UVB%: 6.8
Used Reptisun 5.0
UVB-1: 1.717
UVB-2: 6.663
D3 YI: 367.7
UVB%: 6.6
Reptilight
UVB-1: 1.302
UVB-2: 5.825
D3 YI: 283.7
UVB%: 4.4
Exo-Terra 8.0
UVB-1: 0.780
UVB-2: 6.914
D3 YI: 190.2
UVB%: 4.2
Active UV Heat
UVB-1: 0.815
UVB-2: 14.647
D3 YI: 165.3
UVB%: 1.2
ESU Reptile Desert 7.0
UVB-1: 0.000
UVB-2: 0.443
D3 YI: 0.5
UVB%: 0.3
Conclusions:
The author states: "Of all the lamps measured, the best contributor
to vitamin D3 photosynthesis in skin is Zoo Med Reptisun, with a D3
Yield Index of 439. This result can be considered especially
noteworthy for the fact that the lamp in question is only a 14W
unit, while other units in the study have a nominal power of 30-
40W. The spectrum of Reptisun begins very low in the UVB range and
the spectrum curve rises steeply. In the most sensitive wavelength
for vitamin D3 synthesis, 295 nm, for example, the radiation of
Reptisun is already 1.8 times stronger than that of the next best
lamp.
The second best lamp, a Zoo Med Reptisun unit that had been used for
10 months, does not show remarkable weakening of UVB radiation.
While examining the full spectrum, it can be seen that the
irradiance of the lamp as dropped constantly through the whole
spectrum. This means that the UVB radiation of a lamp does not
cease abruptly, as is sometimes suggested, but seems to get
gradually weaker along with the visible light. On this basis a
recommendation to replace the UV lamp twice a year due to alleged
fading of UVB radiation is at least to some extent unwarranted. The
conclusion is of course based only on one individual lamp;
differences due to manufacturing tolerances, etc. are entirely
possible.
The next best lamp, Narva Reptilight, is also very efficient in
promoting vitamin D3 synthesis with a D3 Yield Index of 284.
Additionally, its spectrum is exceptionally beneficial; radiation at
315-335 nm range which potentially destroys vitamin D3 is very low.
Next comes a group of four lamps (Exo-Terra Repti Glo 8.0, Active
UVHeat, Reptistar and Exo-Terra Repti-Glo 5.0), the results for
which are rather equal. Their D3 Yield Indices are already less
than half of that of the best product. In this group, the case of
Sylvania Reptistar is interesting. Even though its irradiance in
UVB range is the third highest of all tested units, its D3 Yield
Index is only modest. Its spectrum curve starts to rise only at
about 300 nm; therefore, the main proportion of its radiation is
concentrated in the UVB-2 and UVA ranges, in which strong
irradiation is known to be detrimental to the production of D3.
Another sample that attracts attention in this group is Active
UVHeat. The spectrum of this lamp is almost a pure line. In the
wavelengths where radiation exists, it is very strong. In other
areas radiation is at the same level as for the 14W range, at 302-
304 nm - this establishes the D3 Yield Index of this lamp at a
reasonable level. However, its spectrum has another peak, over 10
times higher, at 313 nm, and beyond that generally rather high
irradiance values which may contribute to photodestruction of
existing vitamin D3 in skin....
The Reptile Desert 7% UVB, manufactured by Energy Savers Unlimited
(ESU) turned out to be a disappointment. Despite its name, the unit
only produces 0.3% UVB radiation and its D3 Yield Index is only 0.5."
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