Wood ID

[Bill Jobe]

This might be a good time to mention that looking directly at a uv light can cause permanent blindness.

[John K Jordan]

This might be a good time to mention that looking directly at a uv light can cause permanent blindness.

Are you sure? Are you possibly referring to photokeratitis? Also known as Arc Eye, painful burning of the eye from looking at a strong UV light or a welding arc. This is more like sunburn of the cornea and can have symptoms from mild itchiness to severe pain. However, the cornea heals itself in a day or two. No permanent damage and certainly not blindness. I'm sure you can find something on the internet that claims looking at into a UV light can cause blindness, but both my eye surgeon and eye doctor indicated that's not the case. (I was concerned both about the UV lights I've used for years and my welding equipment.)

I understand longer term exposure to UV light can cause a type of cancer related to the eye, similar to skin cancer, and can contribute to cataracts. This is a good reason to wear UV blocking glasses and sunglasses when outside, especially around water and snow. From my reading, a lifetime of exposure to the sun is potentially far more damaging than using an artificial UV light for fluorescence, sterilization, or curing of adhesives.

If anyone is concerned about using a UV light, especially brighter lights with a shorter wavelength, UV blocking glasses and safety glasses are widely available. Amber or yellow glasses can diminish the blue end of the spectrum as well, easing eye stress from trying to focus on both ends of the spectrum.

For those worried about UV, consider not using LED lights in the shop and house. Some LEDs have been shown to output a significant amount of UV light. Some researchers are concerned we will eventually see far-reaching damage from long term use of LED lights.

But staring into a UV light, an 800 lumen flashlight, your car headlights, or any bright light is not a good idea. I wouldn't stare into a laser light of any kind, although it has been shown the "blink reflex" will protect you from damage from a laser in the visible wavelengths. A bright laser can temporarily blind you for some seconds, though, long enough to wreck your car. (Green is the worst due to the human eye's high sensitivity to green.)

An entirely different issue is invisible light from lasers, specifically intense IR light which will instantly burn the retina. I used to work in and around laser labs and in spite of the rules, some coworkers got instant and permanent eye damage from carelessness, specifically, failure to use the proper eye protection. One guy I worked with dropped a tool which passed through the beam and reflected light into his eye leaving him with a burned line across his vision the rest of his life. Someone put up a somewhat humorous but very serious eye chart - I never got a picture of it but I recreated it for a friend:

eyechart.jpg

JKJ

[Leo Van Der Loo]

Bill this is what is known now, and yes you can get blind from it over time.

UV effects on eyes.jpg

just wondering what all this does to finding an answer to the question of the ID of wood that you asked .

[John K Jordan]

just wondering what all this does to finding an answer to the question of the ID of wood that you asked .

I wondered that too!

I couldn't find anything conclusive relating UV to macular degeneration. I read one case reported but appeared to be independent of and coincidentally found following exposure to laboratory use of UV, more likely related to the age of the patient. As mentioned, the more trusted references for this and other permanent conditions pointed primarily to long-term exposure to UV from the sun. I'll ask my eye professional about this and for updates on other short-term exposure issues the next time I see him. What is the source of the quote you copied?

JKJ

[Bill Jobe]

My comment was something that was thought to be true within another hobby I had years ago...koi keeping. I just assumed those who made that claim knew.
I ran 2 40watt lights and was very careful not to look at them directly when turned on outside of their in-use position.. But while in use one could not see the light because the tubes fit inside of a waterproof pvc body. They did have a lens on one end so you could see if they were on. The lens was supposedly coated with uv blocking material and appeared blue.

[Bill Jobe]

The problem is the manufacturer lies or is mistaken when advertising the wavelength. I've even bought two identical lights from the same vendor and one was good and the other useless for ID.

JKJ

I've found that to be true with residential lighting, as well.
Many led bulbs are labeled with the wrong wavelength.
I once was at a big box store looking for warm leds. A salesperson happened by and I asked him for help. I told him the Kelvin number I was looking for and he said there's no such thing as a Kelvin number for lighting..that it was a measurement of heat. I told him that it is also a measurement of light. He gave me an angry look and told me that he was an engineering student and that he certainly was not going to take anything I said serious, then he walked away.
They may be labeled better now days but a few years back they sold 3000k bulbs that were more like daylight.

[John K Jordan]

I've found that to be true with residential lighting, as well.
Many led bulbs are labeled with the wrong wavelength.
I once was at a big box store looking for warm leds. A salesperson happened by and I asked him for help. I told him the Kelvin number I was looking for and he said there's no such thing as a Kelvin number for lighting..that it was a measurement of heat. I told him that it is also a measurement of light. He gave me an angry look and told me that he was an engineering student and that he certainly was not going to take anything I said serious, then he walked away.
They may be labeled better now days but a few years back they sold 3000k bulbs that were more like daylight.

Maybe he was a civil engineering student. Just refer to the Kelvin number as the color temperature with the emphases on "color" and avoid the whole issue of black body radiation.

The issue with UV lights for wood ID is those whose spectrum spread is indeed 365 nm include very little visible light. Those mislabeled may include some 365 nm light but also put out a lot of light closer to 400 nm or longer which is in the visible blue end of the spectrum. This type will cause fluorescence but it will be so washed out by the visible light it will be difficult or even impossible to see, especially where the fluorescence is naturally weak. A couple of the cheap UV lights I bought even had a lot of white light in the mix. I finally discovered recommendations for a high quality UV light by searching the Candlepower forum. Not cheap but work extremely well.

JKJ

[Bill Jobe]

John, I'm guessing your comment "black body radiation" was humor, but it went over my head. Mind elaborating for this hillbilly?

Surely you are well learned about far infrared radiation, as well. That was another popular subject amongst koikeepers. A breeder in Japan came out with a product made of ceramic, mixed with rice hulls and baked at around 1400F. The results was a product with lots of holes for bacterial to set up shop and far infrared light that supposedly cleaned the water to a level never before available. I checked out the price of adding it to my 4,000 gal. Pond and was shocked to learn my price would be in the thousands if done properly. I decided to pass.

[John K Jordan]

John, I'm guessing your comment "black body radiation" was humor, but it went over my head. Mind elaborating for this hillbilly?

From one hillbilly to another: As defined in science and engineering, a black "body" is the ideal whose surface does not reflect any light. Heat an object and when hot enough it will emit light from the surface, first a dull red, then brighter and whiter and finally bluish white. If the object is ideal black body, the temperature of the object in Kelvins is the color of the light. If the object is not a perfect ideal black body, the color of the light is close to the temperature but not perfect and may not be good for instrument calibration. If the object is not even heated to produce light (such as an LED), a method is used to approximate the Kelvin number. Next time tell the engineering student to look up CCT, or Correlated Color Temperature - every good Home Depot clerk should know this stuff.

Light from sources other than extremely hot things like bulb filaments don't put out exactly the same color of light so they are given a color temperature number close to the black body radiation to give us some idea of the "softness", "warmness", or "coolness" of the light.

I found this chart (disregard the colors they used in the left column); you might find the descriptions interesting:

color_temperature.jpg

This article looks good and explains a bit about the approximations used for non-black body emitters like LED:
http://lowel.tiffen.com/edu/color_te...mystified.html

JKJ

[Bill Jobe]

Thanks for the link, John. Interesting stuff.
I've always been fascinated with light.

I have a theory about light that I may share with you at some time. The few persons I have told walked away shaking their heads. Some avoid me altogether.
That's ok. I enjoy solitude.

[John K Jordan]

I have a theory about light that I may share with you at some time. The few persons I have told walked away shaking their heads. Some avoid me altogether.

I would love to hear your theory - anything that might get me thinking in different directions gets my full attention, even if I don't understand or agree. With throwing out ideas for brainstorming, discussion, and taking turns playing the devil's advocate, everyone expands their bubble and learns something - that's how innovation gets a kick. When working at the Lab we often had lively sessions bouncing around "crazy" ideas. In fact, I have several shared patents based on some of these sessions, coincidentally related to light.

I'll bet some closed-minded people shook their heads and walked away from Einstein and Tesla at times.

Go ahead, hit me with a private message. If something is intriguing and way beyond me I have a friends and associates expert in appropriate fields, some with PHDs in physics and mathematics who specialize in light, lasers, and fluorescence.

JKJ

[Glenn C Roberts]

Bill, You have let us know you may have something very interesting to share. The cat is out of the bag already. Let's hear it! Think tanks are the way to go, even if nobody else is there!

[Bill Jobe]

Here's a shot of the side of an oak bowl.
I think I've posted it before but since then I tried several ways to sharpen the image.
The only thing I don't like about it....it isn't Osage Orange, my current favorite wood.

I think I'm going to drag out some of my camera stuff and experiment. Maybe buy a good lupe, too.
I came across some Argentine Osage and the grain looks much different.