uv weathering testers are used to simulate the effect of ultraviolet from the sun on various materials such as plastics, paints, glues, outdoor clothing or beachwear
between the use of an overwattage electronic ballast and the highly efficient pure aluminium reflector, you can get uv intensities over an area equivalent to panel arrays at a much lower cost, weight, and power consumption and also have improved handleability
what follows is an account of how to make such a lamp that can generate uva or uvb for weathering testing.
salt spray, chlorinated water and other factors can be added in, but be careful of potential electric shock hazards, especially from salt, salt water, or any water
apart from the uv tubes, the lamp is very low cost and also can be used as a bright inspection lamp with a visible light fluorescent in
interestingly, a friend, by passing this lamp with the philips broadband uvb tube (TL 20W/12 RS) over her whole body several days in succession completely stopped severe stabbing pains due to a prolapsed or floppy mitral valve and there are reports on the web of high dose vitamin d (8000? iu daily) reversing aortic valve disease
she also used the compact uvb lamp in the joints section of the compendium, which because it can be held closer gives a higher intenstiy of uvb on the skin and higher vitamin d levels.
whether the compact lamp is a higher skin cancer risk because of this, i don't know, but i rely on the compendium™ and the BCD™, especially the dual seleniums and adequate iodine for protection and am able to use homemade liquid nitrogen probes to remove any suspicious moles.
freezing is much safer than surgery, creates antibodies to the cancer and doesn't spread the cancerous cells in tissue like a scapel does, though its only effective for a depth say to one or two millimeters or so.
electronic ballasts deliver about 10% more light output than equivalent magnetic ballasts, thats what the theory says and what my practical experience is
they are lighter, give a longer lamp life (a critical factor with uv!), and are easier to shield for the magnetic field
electronic ballasts are far easier on the filaments so the life is much longer, especially if they are being turned off and on quite frequently in relation to the "on" time
the primary advantages of electronic ballasts are at an operating frequency of aproximately 25khz, they don't have the 50hz strobe problem that magnetic ballasts have, lamp life is longer and the frequency being higher their magnetic fields can be shielded, it's impossible to shield the 50hz fields of magnetic ballasts, and of course the 10% increased output
low frequency magnetic fields are a real biological hazard stemming from free radicals created from resonance of the iron in cells and blood
one of the most cruel instances of the stupid medical denial of the problems of magnetic fields is premature babies in incubators being placed in very close proximity to the motors that drive the climate control
a 2 ft single fluorescent batten can be bought at an electrical or hardware store and just needs retrofitting with an overwattage electronic ballast and a reflector made from aluminium flashing. photo
the flashing came in a 9 inch wide roll and the length cut to was 589.5mm, but the exact length will depend on the batten
the mains cable to the batten should be three wire (phase, neutral, earth) and the batten case earthed for safety
interior view photo's are below, please consult your local wiring regulations regarding fusing, earthing, cable clamping and the qualifications necessary to build this lamp
note the long screws used to hold the ballast are cut to length to fix the reflector when it is fitted. lock nuts are best for fixing the ballast to the case and also for standing off on the underside of the reflector. on the top side of the reflector i use a washer and thin square nut overall view (660k)
note the cable tie on the mains cable that will have the end cut off so the mains cable can be pulled back and the cable tie act as a stop. it is important that the cable is clamped or otherwise fixed in accordance with local regualtions so that there is no danger of the cable pulling the wires out of the electronic ballast and shorting to the metal case (which must be earthed) mains end (674k)
the aluminium flashing used for the reflector is pure aluminum and not an alloy, this important because mirror finished, pure aluminium reflects uv very well, so well that this lamp gives a surprising amount of uv for just one tube.
"Aluminium is one of the few metals that retain full silvery reflectance in finely powdered form, making it an important component of silver paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3000–10000 nm (far IR) regions, while in the 400–700 nm visible range it is slightly outdone by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper." - wikipedia
alloy alumnium is hard and you can't really bend it, but pure aluminium is soft and bends easily which is why it is used for flashing (replaces the lead they used to use)
the aluminium flashing is the only pure aluminium short of getting an ingot i have come across
also the flashing surface is mirror smooth and shouldn't be tarnished at all
you could use a double tube fitting of course with two tubes and there are different batten lengths for different tube lengths, but the 2 ft single tube and batten is handable and easy to move around, with a pronounced bright zone in the middle portion of the tube (extending from 1/4 way to 1/4 way)
you can overdrive the fluorescent tube to give more light, like say for a 18 or 20w tube you can overdrive it with a 36 watt electronic instant start ballast.
maximal uvb output with an 20 watt tube and 36 watt ballast is at a lower phosphor temperature than the steady state temperature of the tube so you can turn the tube off for five minutes to let it cool so you are operating in the region of optimal phosphor temperature more
you can touch the tube near the end to feel its temperature, maybe an inch and a half from the end, not right over the electrodes though
the osram quicktronic instant start ballast (QTIS e 1x36/220-240) has separate wires to each of the two pins on one end of the tube, the other end has only one wire which can go from either pin to the ballast, but you must link both of those pins together for the best results
T12 = 12 x 1/8th of an inch diameter tube, T8 = 8 x 1/8th, T5 = 5 x 1/8th
with overdriven uv tubes, its best to turn them off when not used, as uv lamps have a limited lifetime compared to ordinary fluorescents.
18W white light fluorescents overdriven to 36 watts seem fine running permanently but their life will be shorter and they need to be well ventilated to prevent heat build up
the output of the tube phosphors are very temperature sensitive, the philips TL 20W/12RS seems to have a maximal output at quite a low tube surface temperature of about say 35C, other lamps will be different though and it pays to use a meter to check the output from switch on to see how the output changes
i sometimes check the temperature of the tube by putting my finger on it about 5cm (2") from the glass facing edge of the metal end cap and i don't worry about the smear mark there, most of the output is in the middle half of the tube
warm to the finger touch is about right for maximal output for the philips TL 20W/12RS tube
if the tube gets too hot, i may turn it off for four or five minutes to cool
tubes should always be given at least a minute between being switched off and switched on again to allow the filament to cool
what ballast you use will depend on the tube, you can of course use the ballast that came with the batten, if its an electronic one, say 18 watts, that can be used, but after some hours use the uv output will start to drop as the wall's of the tubes 'solarize', and drop in efficiency, this is where overdriving the tube comes in to maintain uv output
the batten/reflector assembly needs to be stored face down so it doesn't collect dust on the tube and reflector photo
a small stand can be made with wooden ends mounted on say a 30mm outer diameter aluminium tube the same length as the batten or a length of wood photo
isopropyl alcohol (rubbing alcohol) should be used to clean the tube and reflector as it is grease free, unlike meths.
You can basically build this and test it with the original tube in and fit uv or other tubes when you are ready.
with overdrive it also makes a very bright inspection or moveable workshop lamp
techwest sell uva 'blue black light' lamps and industrial uvb lamps.
The blue black light spectrum is 315nm~400nm and the F20T10.BLB would be suitable (make sure you get the right length tube.)
Techwest also sell a 20w 2ft industrial uvb tube type G20T10E
I think the G20T10E is similar to the philips medical tube TL 20W/12 RS or the generic FS20T12/UVB
prolight in sofia, bulgaria have good prices on uv tubes including philips if the order is large enough to offset the postal cost, like say six tubes
another supplier is hybec in leicester, uk
These tubes, like all household linear and compact fluorescents have mercury in, so don't break them and if you do, be careful about clean up, don't use a vacum cleaner as this just spreads the mercury everywhere
mercury is the most toxic non-radioactive element which is why they put in our mouths i guess ;o)
i tested some slightly grey tinted swimming goggles and they blocked the UVB completely (tested with my 6.4 solarmeter), they will be polycarbonate, but unfortunately the UVA cutoff for that is marginal !
interestingly those swimming goggles also blocked visible violet making the lamp light look light blue which means it was blocking up to about 410nm !
the full type tanning goggles should be fine, i don't know about cones since they may restrict the field of vision too much, use a reputable brand and possibly i'd go for darker lenses, not blue, purple or violet anyway !
i find you can look at a fluorescent UVB lamp without getting a corneal burn if done from a reasonable distance, say three or four meters or more
it's important that you can't see any of the UV light (the visible portion is coloured purple, actual UV you can't see) from the side of your eye, maybe welding goggles are overkill, goggles as per this video are obviously adequate but basically you need some sort of certification/surety about the ability of the lenses to block UV !
any feeling of “grittiness ” in the eyes is a sign of uv getting onto the cornea !
uvb eye burns are excruciatingly painful and can be quite delayed from when you get the exposure to when the pain starts.
UVB and UVC lamps still emit UVA
infrared, though not an issue with these lamps, is an underrated source of retinal damage
its almost essential have uv measuring meters, i use solartech
there's nothing really suitable for uva, but the solarmeter model 6.4 is ideal for uvb.
avoid over long skin exposure close to the uv lamps, i use gloves if holding a uv meter right up close to the tube.
i take tube readings about 5 1/2 cm away from the tube which almost maxes the meter out and gives the best accuracy since 1 count in 2000 is 1/20th of a percent compared to 1 count in 20 which is 5%
in terms of measuring uv output, temperature of the phosphor is a huge factor, you can use your fingers to judge and see the difference, ambient temperature and the length of time the lamp has been on directly affect phosphor temperature
the center of the tube meter reading is much higher than the ends because of the additive effect of the rays along the tube
if you regard the phosphor as being semi transparent then you can also get uv from the other side of the tube coming through or even an additive linear effect of exciting electrons in the tube
linear addition along a line changing an radiative inverse square law into a linear inverse relation is a fairly standard physical phenomenon
shining a torch on the meter display is sometimes needed to enable me to read the meter despite the goggles