UV Lighting and health

[cmoody]

Please forgive me if this has been covered before (I know it's been mentioned for specific things, just not a general thing).

 

Obviously UV lighting is/can be bad for your health, causing skin cancer, damaging your eye sight etc. In my recent research, trying to get this work project set up, I've looked at all manner of lighting options, from converted flash guns, to continuous UV lamps used for curing concrete!

 

Some things I've read have been quite cautious, stating anything below 400nm should require you to wear suitable protection. Whilst other places have suggested that for flashes and the likes the exposure is short enough to not need to worry about it, even though the spectrum is down to 200nm.

 

My question for the experts here, is what you would deem safe exposure? Obviously using a light source designed for curing concrete, or sterilising pond water is quite dangerous and would require adequate precautions to be taken. But what about a camera flash that is 200nm and up?

 

The position I am coming from, is the prospect of taking a few hundred photos a day, for two years (worst case scenario!). A single flash may not be bad, but what about such long term exposure?

[enricosavazzi]

I am not an expert, but I have given some thought to possible UV damage by UV-enabled studio-type electronic flash (with power up to 1,500 Ws, which is much higher than portable battery-powered consumer units). I have not found any definitive studies either.

 

A factor to consider is that we (or I at any rate) use these flash units at much closer range (15-25 cm from the subject) than normal for these units. A 1,500 Ws exposure at 25 cm computes to an equivalent of not more than 6 s of full sunlight. This level of exposure would seem to be too little to cause any concerns, unless you are fully exposed to dozens of discharges a day.

 

On the other hand, damage by UV is known to depend also on the absolute intensity of the irradiation, not only to the cumulative effects of intensity * time. Some organic molecules in the skin are damaged by absorbing one high-energy photon, but the damage is reversible and is repaired. On the other hand, if a second photon strikes the same molecule in quick sequence, the total damage can be difficult or impossible to repair. Therefore, a short burst of photons concentrated in a 1 ms interval can be potentially far more damaging than the same amount of energy over a time of several seconds. Therefore, there could be a potential for far more damage by electronic flash than by direct sunlight.

 

I try to avoid direct exposure to my skin by direct electronic flash, use a polycarbonate full face mask, gloves and long sleeves when using fluorescent tubes that emit below 320 nm, and have developed a habit of closing my eyes immediately before I fire a UV flash. Closed eyelids filter out any UV before they reach the eyes. I wear plastic viewing glasses, so they already filter out UV, but it is practical to avoid temporary blinding anyway. If you are going to do UV flash photography on a regular basis, it might be a good idea to develop habits (e.g. polycarbonate face mask and gloves) to reduce unnecessary exposure to a minimum.

 

Gloves are a rather gray area. Some fabrics filter out UV effectively, others don't. Any clothing with threads sparse enough to show see-through gaps when stretched, like most cotton T shirts, are probably not reliable protection. Thin cotton gloves may not be enough. I looked for gloves designed to protect against UV, but found nothing. I also did not find any reliable UV absorption spectra for thin latex gloves.

[colinbm]

I posted this the other day on another post, but it seems to have been overlooked or went over the top?

http://www.jlab.org/intralab/calendar/archive05/LBC/DeFabo.pdf

Col

[JCDowdy]

Chris,

As a photobiologist experienced in photobiological safety I can address your concerns. With your work expected to entail perhaps hundreds of photos daily for two years your cumulative exposure to whatever source you decide to use will be substantial.

 

The extent of risk and protective measures will depend upon the UV source or sources you employ so that is your first consideration. Intensity is important but wavelength is more important. The spectral requirements of your source should be dependent upon the goal of your thesis. If you are studying UV patterns relative to avian vision there is little utility in including short UV wavelengths significantly below the terrestrial solar spectrum. Likewise there may be justification to further limit the short wavelength range of your source to slightly below the UV sensitivity of avian vision, assuming that is sufficiently well characterized. Restricting the spectral output of the source in this manner is easily accomplished by selecting an appropriate UV long-pass filter. Schott WG-230 type filters are used to model the solar ozone cutoff in Xe-arc solar simulators. The spectrum can be further limited by WG-335 or WG-345 or equivalent filters if the scope of your work (lower limit of avian UV vision) does not require wavelengths these filters attenuate. This will have the added benefit of minimizing the UV photodegradation of specimens that is worrying your collaborating curators.

 

My next question to you is, why do you need to be exposed to the UV? Obviously you must be in proximity to the camera while positioning specimens and setting up the photos. However I recall you will be using professional grade equipment. I expect your cameras are likely capable of remote tethering. I advise you to construct a partitioned area in your studio to fully enclose the specimen and camera stand. This should completely contain any back-scattered UV radiation as photos are taken from outside the enclosure. Portable UV shielding could be assembled if you cannot relocate specimens to your studio. If you, or anyone in proximity have any sort of photosensitive health considerations this may be the only acceptable way to proceed.

 

In the event you cannot avoid exposure, field work for example, first and foremost is the ocular risk. You should invest in quality protective eyewear with side shields and which fit closely across the brow and under the eyes. The under appreciated hazard is scattered UV that can get in behind eyewear. A face shield as Enrico describes is best worn over proper glasses to block scatter, but I do not recommend that in lieu of glasses. A lightweight comfortable pair of padded goggles, resembling what skiers or motorcyclist wear, that seal to the face affords the best protection.

 

Skin protection is best provided by clothing designed for UV protection and is commercially available, look for a high UPF rating. UPF is the clothing equivalent to the SPF rating of sunscreens. There are also fabric treatments that could be applied to any special garments, such as lab coats or gloves, that you may be required to use, just be careful to confirm that residue from treated textiles cannot contaminate specimens or camera filters/lenses. High SPF sunscreens will provide protection to skin not covered by clothing. Obviously sunscreen can contaminate optics or stain specimens and can be difficult or impossible to remove so take great care not to touch items with sunscreen contaminated hands!

 

I am happy to try and answer any additional questions you may have.

[Andrea B.]

Above all, always wear UV protective goggles.

[baffe]

Hi!

 

My flashes are standard-flashes equipped with UV-Filters.

So I don't have more UV than with common flashes. Just less VIS.

I do not care at all.

 

When I make macros one eye is closed and the other is protected cause during flash the mirror is up.

 

! da baffe

[Andrea B.]

Using the viewfinder for UV??? You must have an internal UV-pass filter in camera? That would be interesting to hear about.

[baffe]

Of course not. Sorry.

 

I only take Pictures of flourescence. Not of the UV itself.

[Andrea B.]

Aha !! It all makes sense now. :D

[cmoody]

Thanks all for the input.

 

Any idea whether the UV exposure from using a modified Vivitar 285 (Fresnel lens removed) would be significant?

 

In the past I've spent most of my summers outdoors in the sun doing fieldwork (covered up as best I can, never burnt etc) - but I would have thought/hoped the exposure being outside would be much greater than the camera flashes with the fresnel lens removed? Hopefully most of the UV would be absorbed by the light tent set-up I am planning on using.

[Andrea B.]

The main concern is to protect your eyes so as to prevent cataracts from forming too soon. We all get them with age, but there is no need to speed the process along. Take it from me who unfortunately had to endure a cataract operation in the left eye at far too early an age.

 

UV can also harm the retina.

 

I don't think we have any actual measurements for flashes versus sun.

[baffe]

Hi!

 

Here (about 12° North) we have a Maximum of around 800Watt per squaremeter in direct sunlight and in Summer. Full spectrum.

 

My biggest UV-flashes have about 1000Ws before the filters (full spectrum).

 

So spending one Minute in direct sunlight is certainly much more Radiation (UV and full spectum) than some direct flashes during my UV-Shootings.

 

1000Ws are really big flashes... I don't think the danger to my Skin is very big.

 

As I do my Shootings in darkness the Iris of my eyes is always fully open. So my Retina may be in real danger. A reason to use SLR's.