UV from mercury rectifiers...

[jack]

What's the feeling about the danger of the UV from Hg rectifiers?

There seems to be two diametrically opposed views: Either its safe as the dangerous UV (below 300nm) is absorbed by the glass, or its very dangerous and can cause corneal damage.

Take your pick.

Anyone out there with scientific proof vs. re-iterated apocrypha?

Comments?

[Dave the bass]

They look nice.

Thread shutdown!

DTB

[Mike H]

As usual Google search produces differing points of view.

I would have thought if that bad glass would be coated or be a metal envelope even?

[Ali Tait]

Before you turn the amp on, put yer Ray Bans on..

[jack]

Is there a doctor in the house? (or a doctor called House?)

[Dave the bass]

Ha!

SWIDT?

DTB

[IslandPink]

Nick.
As a lens designer, I would say that it's likely most of the output below 300nm would absorbed in the glass, as not many glass types transmit well down there . I would have to do more research to be sure about this - just need to find any info relating to what the glass type is - probably a low-expansion type like Pyrex . Then I could relate it to existing optical materials and make some estimates of the transmission cut-off.
Oh, just to add something to this - the emission is mostly in discrete lines, and 248nm is a strong mercury line - but getting 248nm through most glass is unlikely - only CaF2, fused silica and one or two of the lighter glasses in the glass chart transmit anything down there .

However - next up is 365nm & likely to form a big part of the output from Mercury vapour ( what you can see is 405nm, though, by the way ) ; I'm not sure how dangerous 365nm is , although like all visible/UV radiation, it's very dependant upon the intensity . This is probably UV-A ?

There is one rather practical test you could do :
Get your rectifier switched on and working ; sit yourself down, wearing dark glasses , near to the rectifier , with your (bare) arm about a foot away from it ; stay there for an hour ; see if your arm comes up with a sunburn later that evening

I really think, unless you are going to be right near the amplifier, there would be any problem with using them, to be honest . Intensity drops off as 1/r^2 after all .

[Paul Barker]

[Greg]

Very clever, Paul

[IslandPink]

Is it worth drawing more conclusions about the status of physicists when the guy who drew the face with sunglasses is the 'clever' one !

No, I think I'll just wash the pots and watch an old episode of 'QI' .
See if I care .....

[Greg]

Is it worth drawing more conclusions about the status of physicists when the guy who drew the face with sunglasses is the 'clever' one !

No, I think I'll just wash the pots and watch an old episode of 'QI' .
See if I care .....

Mark, no intention to offend you was intended. I completely respect your knowledge as a physicist in this particular area. I was simply commenting that Paul had been clever to use an emoticon that was particularly relevant to the subject, following on from what DTB contributed. My post was intended to be a light hearted observation. Your contribution to Nickds1's original post is a serious response and I completely get that. Please understand, I'm just having fun. I have no intention of spoiling this thread.

[IslandPink]

I know, don't worry Greg, I was only feigning offence a bit there ; it was a clever response from Paul !

[JamesD]

Speaking as a physicist and amateur astronomer who has tried designing apochromatic lenses - I am in awe of Mark and what he does professionally...

He does it all with mirrors and omits the smoke

OK; and lenses...

J

[jack]

Lot of physics-types here I'm an EE/Physics/Maths bod too...

It seems, looking at the real facts, that the glass is likely to absorb pretty much everything under 300nm, leaving just the UV-A being radiated.

for a good read, see: https://en.wikipedia.org/wiki/Mercury-vapor_lamp

The following quote from the Wikipedia article is quite interesting... " UV radiation can still pass through the outer bulb of the lamp. This causes the ageing process of some plastics used in the construction of luminaires to be accelerated, leaving them significantly discoloured after only a few years' service. Polycarbonate suffers particularly from this problem, and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp to have turned a dull, 'ear-wax'-like colour after only a short time. Certain polishes, such as Brasso, can be used to remove some of the yellowing, but usually only with limited success."

The implication here is that if you have any polycarbonate near an Hg rectifier then it will most probably discolour from the UV-A...

[shane]

Oh, just to add something to this - the emission is mostly in discrete lines, and 248nm is a strong mercury line - but getting 248nm through most glass is unlikely - only CaF2, fused silica and one or two of the lighter glasses in the glass chart transmit anything down there.

This intrigues me. When I worked at Plessey, I was involved with photolithography steppers. These use the output of a 1KW mercury light source to project the image of the design of a microchip onto a silicon wafer covered in photo-resist, which is then developed and sent for further processing with the resist pattern determining the circuit design. The shorter the wave-length of the light, the smaller the feature that can be printed, and the steppers we used were Canon FPA1550s, which worked on g-line (435nm) and could print down to about 0.8um, and ASM PAS5500s which used i-line (365nm) and could get down to 0.35um reliably and 0.18um at a push. That was 1995 technology, and it was all achieved using quartz lenses about the size of a dustbin (and about half a million quid a piece).

The processor in your i-phone is made using steppers which print minimum features down to 40nm, about one tenth the size that ours could achieve, using calcium flouride lenses. How on earth do you make a large high-precision lens system out of what is effectively salt?