- Joined
- Aug 6, 2013
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- 420
As to the subject, one source material was Men's Health (something I clearly never read, and can prove it, should it come to that) which itself quoted the ACGIH Threshold Limit Values, a copy of which lives on my desk. This is the annual compendium of quantified acceptable human exposures to chemical and physical hazards. Due to its species-specific focus, the numbers are of limited utility (i.e. reptile bulbs are supposed to generate UV unlike home use bulbs) but some of the mechanisms involved seem relevant.
For example, the primary hazard in broadband incoherent sources is photo keratitis, primarily in undetected wavelengths, as the aversion response is not triggered. This is counter intuitive in regards to UV reptile lamia as reptiles are tetrachromates and in fact see into the UVA and UVB. (Bowmaker, J.K. 1991. The evolution of vertebrate visual pigments and photoreceptors, p.63-81. In Cronly-Dillon, J.R. and Gregory, R.L. Vision and Visual Dysfunction Vol. 2: Evolution of the Eye and Visual System, CRC Press, Inc. Boca Raton, Florida.)
The closest relevant graph I have is of a starling, fortunately the relevant opsin is conserved so is illustrative.
View attachment 91834
In this case, the detection in the 300nm range corresponds with that which is biochemically active in Vitamin D synthesis. Given all that, the questions would be 1) if the UVB is too bright, why isn't it simply avoided? In this scenario, the expectation is that affected torts would burrow or hide, rather than suffer damage.
2) why is the capacity for damage intermittent and independent of adherence to operating instructions.
My hypothesis is that the answer lies in the UVC range, which is something I manage in germicidal laboratory lamps. UVC for all intents and purposes does not exist on earth due to strong scattering and absorption by O2 and O3. So in addition to higher energy, by virtue of shorter wavelength, UVC would be undetectable to the torts eye (and UVB meters) and worse, they would be attracted to the UVB that accompanies it.
As to the proximal cause of UVC production, the mechanism of phospors is to absorb short wavelength optical radiation and fluoresce longer wavelength, usually in a broader band. So damage or discrepancy in the coating would result narrow band, short wavelength emissions. Perhaps the small tube and coiled shape increase this likelihood?
This remains a conjecture, not a conclusion, but the upside is it's testable. So with that, I'm off to damage some CFL's
Cheers
And now, on with our story, with some qualification. First, I pursued this as an investigation of concept. I don't have the resources for an industry wide study. Also, the equipment used was either misappropriated from it's intended purpose or personally modified/built. We're talking about indicators here.
Anyway, first observations of cfl bulbs, both UVB and general use, include what's called 'ugly light'. The light spectrum generated has a few very high spikes with large gaps in between. (Note: my 'spectrometer' was constructed with a diffraction grating, and a telescope so no numbers for now. I'm trying to borrow one though). This will cause headaches and eye strain even with appropriate lumens ( in humans). Secondly, the flicker rate adds insult. It varies to the point of playing havoc with a light meter if it is direct read and not displaying median values. All of the above applies to every cfl I looked at, including general use.
As to the UVB; one of the persistent ideas I heard was that physical trauma to the bulb would change the intensity or wavelength. I only had a dozen or so to play with, but I could not generate this result and I tested all to failure. (Safety note: be careful trying this at home. Mercury vapor is definitely hazardous).
The next line of inquiry was my own supposition that UV CFLs might be generating short wavelength UVB and potentially UVC. This I was able to verify, albeit qualitatively. Put simply, my meter is tuned to germicidal lamps, so at the extreme low end of the scale, the numbers aren't reliable. It's like measuring a hatchling on a scale calibrated to pounds. The little bump isn't readable, but in the case of these bulbs, the bump shouldn't have been there at all.
Finally, the reflector hood creates essentially a parabolic mirror, which focuses the (at least in some cases) too-short wavelength light to a narrow beam. By altering hood and distance combinations, intensities could vary wildly between points only inches apart.
The most frustrating aspect was the inconsistency. I don't pretend that 14 bulbs constitutes a valid sample, but the typical brands of various ages were represented and the different intensities and wavelengths was striking.
The leading candidate then seems to be a combination of flicker/frequency that inhibits appropriate eye dilation, short wavelength emissions that are both high energy and invisible so don't trigger an aversion response, typically used with a reflector that exacerbates the potential for harm.
That's all I have for now.
Peace out!
Steve
