Brad DeLong's Semi-Daily Journal: A Weblog

The market provides a heck of a lot of choices we like. We libertoonians are funny that way.

"So why can't a $6000 UV source be replaced by a black light from the local stoner supply house?"

Just guessing, but two reasons could be (1) because the stoner black light doesn't supply UV light of the frequency needed, or (2) the SBL isn't tuneable, and the ability to vary frequencies is needed for the work.

"So why can't a $6000 UV source be replaced by a black light from the local stoner supply house?"

In our shop we use a UV glue that the manufacturer recommended a $6,000 UV light system to cure. Though the $12 stoner supply store bulb didn't quite work (tried that) I was able to buy a pair of $100 Sylvania 100w UV bulbs (combined with another $40 in capacitors, etc) and we've been merrily working away with them for the last seven years.

$6,000 vs $12 is a false dichotomy.

my understanding is that the intensity of light coming from a source such as the stoners' UV light is not as stable over time as the $6000 source. For growing bud or irradiating a chemical reaction, that is no problem, I know of chemists using such bulbs, but for spectroscopy, the cheap source is not stable enough.

Chad Orzel is most definitely not fafblog.

A $6,000 uv source could be a tunable point source, which works in a completely different way from any uv light bulb.
That would be like saying, why buy a $5000 laser when I can get light bulbs at the supermarket?
Or why make a $500,000 electron gun when my cathode ray tube in the tv shoots electrons.

This does remind me of the time my tutor at college tried to cure a sore throat by shining a high-intensity UV source borrowed from the university physics labs on his throat for a few seconds...

(To recap his logic. Sore throats are caused by bacteria in the lymph glands. The lymph glands are just below the skin. Bacteria are very vulnerable to UV light).

He had to wear a scarf to cover the resulting sun burn for a few weeks afterwards. Never trust a theoretical physicist with the real world, folks.

Really Richard?
People seem to trust us over here at NASA, where we have plenty of dangerous equipment and 10% of the staff are Theoretical Physicists

Richard 1, Leslie 1.

A room mate once bought a $15 blow drier from Walmart instead of the more expensive $100 Scientific version. Not only was it $85 cheaper, it included a brush.
Forget the scientific supply houses. Shop Walmart Scientific.

a friend of mine who worked at an audiophile-grade audio component company told me about how they tested equipment that was meant to work on foreign voltages.

if they needed, say, 220V at 50Hz, rather than order specialized equipment of some sort, they would take a signal generator (of which they had plenty kicking around) and one of the high-end high-power power amps the company made, hook up the signal generator, and crank the gain on the amp until the speaker output was at the appropriate voltage.

it tended to produce significantly cleaner power than they could expect to get in a real-life power mains situation, but it certainly worked for their purposes.

Richard: The question is, did it cure his sore throat? ;)

Leslie,
Not trying to be a troll or make light of serious events, but NASA's track record isn't exactly perfect....

"People seem to trust us over here at NASA, where we have plenty of dangerous equipment and 10% of the staff are Theoretical Physicists"

Posted by Leslie Walcott

Of course, another way to interpret that is that NASA requires each TP to be watched by 9 normal people :)

Just guessing, but two reasons could be (1) because the stoner black light doesn't supply UV light of the frequency needed, or (2) the SBL isn't tuneable, and the ability to vary frequencies is needed for the work.

#1 is closer. I'm looking for a specific wavelength of UV light (124 nm, a resonance line in krypton), and your typical stoner black lights don't provide much at that wavelength. Light at other wavelengths will be wasted at best, and might be counter-productive, so the line lamp is a better solution. Also, I'm hoping to get the NSF to pick up the tab...

Chad Orzel is most definitely not fafblog.

But, but, but... I was Fafnir all along! Surely that counts for something...

Stoner bulbs, if I remember, provide most of their light at the red edge of ultraviolet--350 nm on up. And not much, at that. They could do better, but think of the product liability suits!
There are zillions (okay, dozens) of UV light sources for those who need something either more intense or shorter wavelength. For my money, a xenon lamp works fine into the mid 200s, or even lower. Mercury is fine, if you don't mind a spikey output. But I don't remember either costing $6000.

Most Stoner bulbs have glass envelops which cut off at ~ 320 nm. This is not useful if you need the 254 intercombination line or the 185 nm resonance line.

By the time you get through paying for the power supply for a fancy discharge lamp, the cost can be high (but there is always Ebay!!)

My personal favorites were buying a 2 x 1 m marble table top from a gravestone cutter instead of a $15K optical table. He was thrilled, we were the only happy customers he ever had.

The other was figuring out that a cooler in a laser could be substituted for by a motorcycle radiator. That was about 2 orders of magnitude in dollars. The motorcycle guys giggled about that one also. One of the tricks is to tell the folk you buy these substitutes from what you are doing. They see the humor in the situation and give you great service. If you listen you can often learn how to do what you want better.

A hairdryer!

Thank you Bakho. how serendipitous. I've been scratching my head all night trying to think of a inexpensive device to provide a low but steady airflow.

He claimed it had cured his sore throat (let's be honest, after what he'd done to himself, he had too), though I was very sceptical.

My other tutor's sole commment was 'he's mad'.

I thought this was fafblog?

hrm. link didn't stick, here ya go:

http://techhouse.brown.edu/cgi-bin/photojoe.pl?basedir=/photos/&dir=20010528%20Commencement%202001&pic=052835chrisfafmgb.JPG&thumbs=

This takes me back! Years ago I used an "Evenson cavity" to excite discharges in rare gases for spectroscopic work. Broida et al. at what was then the National Bureau of Standards (now NIST) had designed the cavity to work with microwave at ~2457 MHz because that microwave frequency was generated by medical "diathermy" units, cheaply available, used, on the surplus market.

The other side of the market was told to me by a chem grad student who had toured the plant of a very large and well-known scientific instrument company, that supplied columns for gas chromatography. One of the chromatographic supports used was a detergent surface, so you poured a detergent into the column tubes -- the company sold detergent in small, very expensive packages (and customers presumably believed that this was some specially designed detergent). The grad student reported that folks on the packaging line were opening large cartons of Tide and pouring from them into the tiny packages they sold.

Does anyone here from Cambridge remember Eli Hefron's? How about Bozo 109 speakers?

How about Tang cocktails? Why buy vodka for screwdrivers when you can get 200 proof lab alcohol cheap? (Oh yeah, there's the benzene to get past the azeotrope).

I had some friends who wasted a lot of time learning the difference between carbon dioxide sold chemically pure (CP) and sold biologically pure (BP).

Sometimes you have to pay for precision, but sometimes you don't.