LED Shop Lighting

[seal killer]

Patio--

It helps!

Thanks.

--Bill

[SteveHGraham]

Back when I was taking modern physics (elementary quantum mechanics and relativity), my prof told me something interesting. Anything you heat up will glow with the same color (spectrum, really) at a given temperature. If you heat titanium and iron to the same temperature, they will look the same. I assume this is where the notion of rating lighting colors in Kelvins came from, but I don't know.

He told us about a device called a pyrometer, used in the steel industry to gauge temperature. It's a thing you look through, and it lets you compare the color of hot metal to a reference color. The Internet says the little hand-held IR remote thermometers are also called pyrometers, but he was talking about an optical thing.

Oh, hey! Here it is: https://en.wikipedia.org/wiki/Color_temperature

[seal killer]

All--

I cannot find LED tube lighting fixtures--those that come with the LED tubes permanently mounted--without a pigtail and 110v male plug. That means I would have to install a 110v outlet for each 8' fixture. I have an electrician friend that did exactly that. But, not being able to easily daisy chain those fixtures somehow bothers me. I will have three rows of four 8' fixtures in the garage. That means 12 outlets. If they are all dual outlets, that would also provide an additional 12 outlets up there for whatever. Not too handy, but maybe I could use them.

--Bill

[seal killer]

Steve--

If you heat titanium and iron to the same temperature, they will look the same.

If two dissimilar metals are heated to the same temperature, they will produce different spectra. (I think you may have meant that, but worded it wrong.)

--Bill

[BadDog]

You can cut the pigtail off and wire it into a J box just like other fixtures. But you may have to reroute the wire through the back of the fixture or otherwise deal with the unsightly visible pigtail.

I bought some relatively inexpensive LED fixtures from Amazon for my home office. They do not have pigtails and wire in like a typical florescent fixture. This is what I got. I usually go for the 5k, but these provide plenty of light and work well in my office. They are not particularly aesthetically pretty, but work very well when you don't have or don't want to keep the fluorescent T12/8 fixture. But when I bought mine, they were less than $40 each. And in my case, my office had bare 2 tube 4' T12s with no reflector or diffuser, and I wanted something a little nicer. I also wired them 2 lights to each of 2 switches. With all 4 on, it's as bright as you could want for detail work, but a little too bright for setting in front of monitors all day (my job). So most of the time I only run 2 that are located more or less above my head. Works well for me.

[seal killer]

BadDog--

Hey! Thanks for that link.

--Bill

[Harold_V]

Back when I was taking modern physics (elementary quantum mechanics and relativity), my prof told me something interesting. Anything you heat up will glow with the same color (spectrum, really) at a given temperature.

Hmmm. I wonder if the professor had any experience with melting (pure, as in not alloyed) gold. While I may be wrong, I don't know that I am. When one observes molten gold, it emits a green hue. Gold melts at approximately 1950°F, and is very pretty to see for those who haven't "been there, done that".

I make mention because it is distinctly different from observing molten copper, which melts at approximately the same temperature.

H

[John Hasler]

Steve writes:
> Back when I was taking modern physics (elementary quantum mechanics and relativity), my prof told me something
> interesting. Anything you heat up will glow with the same color (spectrum, really) at a given temperature.

That's true of a bl;ackbody but not exactly true of metals. Different materials have different emissivities at different wavelengths. The hotter something gets the closer it gets to being a blackbody, though.

> If you heat titanium and iron to the same temperature, they will look the same. I assume this is where the notion of rating
> lighting colors in Kelvins came from, but I don't know.


The idea is that a 5000K light source will look just like light from a 5000K blackbody. The Sun is very close to a 6000K blackbody.

[WesHowe]

He told us about a device called a pyrometer, used in the steel industry to gauge temperature. It's a thing you look through, and it lets you compare the color of hot metal to a reference color.

I have seen those used, over 40 years ago. It was so important that a member of management brought it down, the furnace operator spilled some iron on the sand atop the floor, and the reading was taken. When approved, they would tap the furnace and begin their casting process. I was driving a truck back then, and had to wait for all that to complete to get loaded. Such inefficient processes, no wonder foreign steel operators cleaned out the U.S. steel industry.

- Wes

[wlw-19958]

Hi There,

How does this fit into spectroscopy (that is, the
analysis of an unknown compound through the
spectrum of the electromagnetic radiation of
the different wavelengths emitted when the
unknown is heated to the point they emit light)?

Good Luck!
-Blue Chips-
Webb

[seal killer]

Webb—

I’m not sure it does fit into spectroscopy. I may have mistaken Steve’s comment to mean spectroscopy when that was not the case.
—Bill

[SteveHGraham]

I probably should not have brought this up, as it's something I learned about 26 years ago, and I don't recall exactly how it works. I just thought it was interesting.

Professor Huerta was not an engineer, so he may have been wrong about all materials glowing with the same temperature at given frequencies, but optical pyrometers do exist, so it must be possible to measure the temperature of a known material by the color. Today I learned that there is something called a "disappearing filament pyrometer." I haven't looked it up, but from the name, I think we can guess how that works.

When Dr. Huerta made his apparently controversial remark, we were studying blackbody radiation and the "ultraviolet catastrophe," as an introduction to energy quanta, and his comments were incidental to that. A blackbody is an imaginary, ideal absorber and emitter of energy.

A solid body will emit a spread of EM radiation that forms a hump on a graph of wavelength v. temperature, and the hump, which tapers to zero at both ends, moves down the wavelength scale (toward x rays and other high-energy rays) as the temperature goes up. You can see it as the colors of a heated object change in the order laid out in the spectrum. Red-orange-yellow, and so on. I don't know why the next color is white instead of green, but I'm sure there's an explanation. I saw a website that says the frequencies add until you get white light.

Cooler things emit IR radiation, which we can't see, but they do glow, as you can see when you look at IR video.

I think it was Max Planck who wondered why a hot body wouldn't give off an infinite amount of short-wave RF and fry anyone who looked into, for example, a hot oven. It turned out everything made sense if you assumed that energy was packaged in discrete bits called quanta, which can't be smaller than certain values. Quantum mechanics explains why a hot body gives off a limited spread of radiation instead of a flat graph of waves at all frequency levels. Do not ask me why, because I don't remember.

Anyway, this is where temperature ratings for lights come from.

Interestingly, at least to me, the little pistol IR thermometers they sell at hardware stores are really pyrometers. They look at the invisible glow of solid objects and determine their temperature, and it appears to work regardless of the material.

I am checking Wikipedia now, and here is something relevant:

The higher the temperature of a body the more radiation it emits at every wavelength. Planck radiation has a maximum intensity at a specific wavelength that depends on the temperature. For example, at room temperature (~300 K), a body emits thermal radiation that is mostly infrared and invisible. At higher temperatures the amount of infrared radiation increases and can be felt as heat, and the body glows visibly red. At even higher temperatures, a body is dazzlingly bright yellow or blue-white and emits significant amounts of short wavelength radiation, including ultraviolet and even x-rays. The surface of the sun (~6000 K) emits large amounts of both infrared and ultraviolet radiation; its emission is peaked in the visible spectrum.

Maybe Marv Klotz will pop up and correct all this.