Kirkie
08-05-2011, 08:25 AM
I received the following via a Yahoo group. Its by Frances Baines of UV Guide and was in response to a query about Redfoot lighting. I think it shows how the thinking is moving away from the provision of doses of shortwave UVB (your UW/CM2) to an idea that if you replicate full spectrum sunlight the reptile will be ok, vitamin D3 wise.
It may also put Alans mind to rest about his dodgy Solarglo's. :)
Throw away your Solarmeter 6.2, get a 6.5. :) :)
As you know, your red-footed tortoises are a forest species, so they would probably not expose themselves to midday sun; but bask in morning shafts of sunlight coming through the trees. So you're absolutely right, 200 uW/cm2 might be fine if it was sunlight that you were offering them. 200uW/cm2 of sunlight (measured on a 6.2 Solarmeter)is equivalent to about UVI 3.5 (measured on a Solarmeter 6.5)- that's about what you'd get in full sunlight in the tropics at about 8.30am.
However, mercury vapour lamps have totally different spectra, which usually have a higher proportion of UVB in the shorter, more photoreactive wavelengths (more "powerful" in terms of their effect on skin).
So the reading on a Solarmeter 6.2 (which measures the whole of the UVB region, not just the shorter wavelengths)from sunlight can't be compared to the reading from a mercury vapour lamp. It's a bit more complicated. I use a combination of a 6.2 and a 6.5 meter and work out a formula for converting the readings to UV Index units.
What brand of mercury vapour lamp do you have? It makes a great deal of difference.... If it's a fairly well known brand that I've measured recently, I can give you a rough idea of what the Solarmeter reading would be, to make the "strength" of the UVB roughly the same...*
To get about UVI 3.5 with one of the new MegaRay Solar Raptor 100-watt bulbs, you'd want to aim for readings of about 140 uW/cm2. 200uW/cm2 from one I measured last week would give a UV Index of 4.9. That's fine, but it's more like full tropical sun a bit later in the morning, maybe around 9.30am.
If you were using a ZooMed Powersun 100W, however, you'd want to aim for readings of only about 40 uW/cm2. These have a far higher proportion of their output in the shorter wavelengths. 200uW/cm2 from a new 100W Powersun I measured last August would give a UV Index reading of UVI 18.5. That's higher than the strongest tropical sun at sea level on the equator.
It may also put Alans mind to rest about his dodgy Solarglo's. :)
Throw away your Solarmeter 6.2, get a 6.5. :) :)
As you know, your red-footed tortoises are a forest species, so they would probably not expose themselves to midday sun; but bask in morning shafts of sunlight coming through the trees. So you're absolutely right, 200 uW/cm2 might be fine if it was sunlight that you were offering them. 200uW/cm2 of sunlight (measured on a 6.2 Solarmeter)is equivalent to about UVI 3.5 (measured on a Solarmeter 6.5)- that's about what you'd get in full sunlight in the tropics at about 8.30am.
However, mercury vapour lamps have totally different spectra, which usually have a higher proportion of UVB in the shorter, more photoreactive wavelengths (more "powerful" in terms of their effect on skin).
So the reading on a Solarmeter 6.2 (which measures the whole of the UVB region, not just the shorter wavelengths)from sunlight can't be compared to the reading from a mercury vapour lamp. It's a bit more complicated. I use a combination of a 6.2 and a 6.5 meter and work out a formula for converting the readings to UV Index units.
What brand of mercury vapour lamp do you have? It makes a great deal of difference.... If it's a fairly well known brand that I've measured recently, I can give you a rough idea of what the Solarmeter reading would be, to make the "strength" of the UVB roughly the same...*
To get about UVI 3.5 with one of the new MegaRay Solar Raptor 100-watt bulbs, you'd want to aim for readings of about 140 uW/cm2. 200uW/cm2 from one I measured last week would give a UV Index of 4.9. That's fine, but it's more like full tropical sun a bit later in the morning, maybe around 9.30am.
If you were using a ZooMed Powersun 100W, however, you'd want to aim for readings of only about 40 uW/cm2. These have a far higher proportion of their output in the shorter wavelengths. 200uW/cm2 from a new 100W Powersun I measured last August would give a UV Index reading of UVI 18.5. That's higher than the strongest tropical sun at sea level on the equator.