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UV LEDs for curing varnish?


Fjodor
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Some years ago I asked about UV leds for curing varnish. I.e. making a drying box with leds instead of light bulbs.

The opinion at the time was that they were not up to the task yet.

Some days ago I stumbled upon a blog by Andrew Carruthers who has built an drying box with UV LEDS.

http://www.andrewcarruthers.com/led-light-box/

He lists some PROS and CONS with his LED setup:

LED Pros

- low energy use and consequently…

- temperature and humidity very close to ambient. This means less neck movement and popping seams

- low running and maintenance cost. Longer bulb life without deteriorating performance over time.

- Health: UVA spectrum is less damaging for eyes and skin, than the UVB spectrum fluorescent bulbs usually prefered by violin makers. Apart from taking the photo below (while wearing shades) I still treat the lights, which are very bright, as harmful, switching off before opening the cabin.

- low profile, more robust bulbs give more working space – or smaller cabinet

- low voltage feels safer

LED Cons

- Higher set up cost

- UVA cures varnish less aggressively than UVB (This is off set by the greater light intensity from LEDs) and may not work with all varnishes

- My UVA LED light box doesn’t tan wood as aggressively as the old UVB fluorescent light box.

I ordered a set of cheaper UV LEDS from ebay for testing purposes. 5 meter 300 LED strip 5050 395-400nm spectra with a 12v 6A power source (ca 30 euro) and

intend to test if it can dry oil varnish. I will report back.

Does any one else has experience with UV LEDS?

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I had never even thought of UV LEDs.  There seems to be lots of them in UVA,UVB,and UVC.  If you were here in with me in South Texas today I think you would be able to sun tan an instrument but you might have a hard time keeping it from bursting into flames!!  We are well into real Del Rio Summer weather.  Probably won't stop until November or so!

 

dlb

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Thanks

If I understood correctly LEDs can only be produced with a narrow  emitting spectra. 395nm would be at the end of the UVA spectra. Interestingly the leds Carruthers linked to were listed as around 440nm.

Carl, what variety do you have?

 

I'll have to check - I know I got them from Mouser.... 

 

LZ1

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I thought about trying them but I didn't have time for that yet, and my tubes are still ok.

I wonder if it's a good idea to have one single frequency, I would think that a broader spectrum is better.

Unless one knows exactly what frequency one needs for a particular varnish.

And tanning the wood might require a different frequency...

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There is a threshold frequency (or wavelength) where tanning and varnish drying kick in. This is related to the "photoelectric effect". You can have all the light you want, but if the frequency does not have the right energy, nothing happens. Beyond this threshold the reactions take place. Albert Einstein received the Nobel Prize for his theory of the photoelectric effect - not for relativity theory. 

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I thought about trying them but I didn't have time for that yet, and my tubes are still ok.

I wonder if it's a good idea to have one single frequency, I would think that a broader spectrum is better.

Unless one knows exactly what frequency one needs for a particular varnish.

And tanning the wood might require a different frequency...

 

I've tried many different types of varnishes in my BL 350 UV box. It's dried them all. I have a Pine resin varnish that I made (burnt it!) that is touch dry in 4 to 5 hours. Very fast but that's probably because it was super heated. Typically a Pine resin varnish will take 7 to 8 hours to touch dry.

It also tans wood. Perhaps not as fast as other wavelengths but then I wouldn't really know. I've just used the BL 350's.

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There is a threshold frequency (or wavelength) where tanning and varnish drying kick in. This is related to the "photoelectric effect". You can have all the light you want, but if the frequency does not have the right energy, nothing happens. Beyond this threshold the reactions take place. Albert Einstein received the Nobel Prize for his theory of the photoelectric effect - not for relativity theory. 

Michael, you are a man after my own heart!  Not many people know about Einstein and the photoelectric effect.  1905 was a hell of a year!  When ever anyone gets to big for their britches all you have to do is think of the myrical year papers, pretty good for a patent office clerk.  I saw a video a while back that showed a glass plate from the Lick Observatory that was used to prove relativity, imagine the the real plate!  I got to see the Zeiss blink comparator at the old Lowel observatory in Flagstaff that was used to find Pluto.  I love that stuff.

 

dlb

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Interesting!

Let us know how it works, if you also could put some wood wedges in the box and weigh them before and after to see if it also dries wood.

Yep, I thought I try them on a small sample first before I build a box. If it works for curing I will make a box and try to leave some wood in for a longer time to see if it is any good for tanning, I could do some drying tests at the same time.

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Dwight,

 

I shook hands with Clyde Tombaugh. Does that top you?  :lol:  :D  Nevertheless, you visited Lowell. Wow! I did not.  :(

Yes, it sure does!  Our 'Cello teacher at Interlochen was an amateur telescope maker.  he gave me my appreciation for technology and fine mechanical things.  He owned a 1703 Gofriller 'cello when I knew him.  You could look at it for months.

 

DLB

 

The Discovery channel folks have built them a new observatory further outside of town with a big new telescope.  The original observatory has Lowells grave site, and the Clark Refractor is still functional.  They use it more for education and public viewing.

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If these work for drying varnish, I'm in.  You could line a metal trash can with a couple of these strands and get great light distribution IF they will dry varnish.

This is what I had in mind. You could tape the strip in a spiral inside a trash can for an easy installation. For a cello something bigger is requried of course.

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