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Spectrometer
Hi, I just had a chance to play with a spectrometer. It's just a little
cheap one that belongs to my sister-in-law who teaches 4th grade. Naturally, I took a look at my plant lights. I remember being told that all you really need is cool white fluorescents. Of course, being an orchid grower, good enough is never good enough. Some people add warm whites. I don't, but I do add in some Gro-lux wide spectrum tubes. They look very pink so obviously they add in some of the red spectrum missing in cool whites ... or do they? I'm looking through the spectrometer at a cool white and there is a bold bright line in the blue range at about 435 nm, a bright green line at about 535, and a good red line at just over 600. Then I look at the wide spectrum tube, and it looks just the same except there is no red line. Now I'm wondering how the tubes can look pink but have less red that a cool white? I know... there are places on the internet that show a very accurate spectrum for many kinds of light. Maybe that would answer my question if I looked long enough. Of course, I also took a look at my metal halide lights and the HP Sodium light. My comment on the MH is that there certainly is a lot going on in the green part of the spectrum where the light isn't very useful. I couldn't really isolate the HPS bulb because it shares a fixture with another MH bulb. I could unplug the MH but there is a window right next to it with sun streaming in at the moment. After sunset, it might be worth checking the HPS alone. Steve |
#2
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Spectrometer
Steve, with flourescents the line spectra are from the gas within the tube. The
first one sounda like neon; the second one should be as well, I would have thought, but I've no idea where the red line went. The fluorescent coating on the inside of the tube is what is intended to provide the illumination - it fluoresces when electrons & ions from the gas (neon) discharge within the tube strike it. The fluorescent coating should provide a continuous spectrum, weighted towards that end of the spectrum it was designed to provide - ie the blue end for a "cool" tube" & the yellow/red end for a "warm" tube. This continuous spectrum is what you should be concentrating on - not the gas lines. Mwtal halide lamps are still hot wire lamps - ie a continuous spectrum. But they get much hotter than a normal tungsten lamp - more efficient illumination that way. Anyway, a hot wire will still give a continuous spectrum. The lines you see would probably relate to the halogen gases which fill the tube. Your sodium lamps should show quite a colourful line spectrum, with two prominent yellow Na D lines that provide the characteristic amber sodium colour. On Sun, 22 Jan 2006 15:19:12 -0500, Steve wrote: Hi, I just had a chance to play with a spectrometer. It's just a little cheap one that belongs to my sister-in-law who teaches 4th grade. Naturally, I took a look at my plant lights. I remember being told that all you really need is cool white fluorescents. Of course, being an orchid grower, good enough is never good enough. Some people add warm whites. I don't, but I do add in some Gro-lux wide spectrum tubes. They look very pink so obviously they add in some of the red spectrum missing in cool whites ... or do they? I'm looking through the spectrometer at a cool white and there is a bold bright line in the blue range at about 435 nm, a bright green line at about 535, and a good red line at just over 600. Then I look at the wide spectrum tube, and it looks just the same except there is no red line. Now I'm wondering how the tubes can look pink but have less red that a cool white? I know... there are places on the internet that show a very accurate spectrum for many kinds of light. Maybe that would answer my question if I looked long enough. Of course, I also took a look at my metal halide lights and the HP Sodium light. My comment on the MH is that there certainly is a lot going on in the green part of the spectrum where the light isn't very useful. I couldn't really isolate the HPS bulb because it shares a fixture with another MH bulb. I could unplug the MH but there is a window right next to it with sun streaming in at the moment. After sunset, it might be worth checking the HPS alone. Steve Dave Gillingham ------------------------------------------------------------------------------ To email me remove the .private from my email address. |
#3
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Spectrometer
I don't know that I agree with that, Dave.
It is my understanding that the energized gas in the tube (typically a small amount of mercury in an inert gas like argon) emits photon energy in the ultraviolet part of the spectrum as the ions "collapse" to a lower energy state. It is the UV that excites the phosphors, and they are solely responsible for the visible light emitted. That phosphor composition is varied to give different spectral " blends." Neon would be a terrible gas to use in a fluorescent light, as the red color of neon emission shows it to be insufficiently energetic for causing anything to fluoresce. -- Ray Barkalow - First Rays Orchids - www.firstrays.com Plants, Supplies, Artwork, Books and Lots of Free Info! "Dave Gillingham" wrote in message ... Steve, with flourescents the line spectra are from the gas within the tube. The first one sounda like neon; the second one should be as well, I would have thought, but I've no idea where the red line went. The fluorescent coating on the inside of the tube is what is intended to provide the illumination - it fluoresces when electrons & ions from the gas (neon) discharge within the tube strike it. The fluorescent coating should provide a continuous spectrum, weighted towards that end of the spectrum it was designed to provide - ie the blue end for a "cool" tube" & the yellow/red end for a "warm" tube. This continuous spectrum is what you should be concentrating on - not the gas lines. Mwtal halide lamps are still hot wire lamps - ie a continuous spectrum. But they get much hotter than a normal tungsten lamp - more efficient illumination that way. Anyway, a hot wire will still give a continuous spectrum. The lines you see would probably relate to the halogen gases which fill the tube. Your sodium lamps should show quite a colourful line spectrum, with two prominent yellow Na D lines that provide the characteristic amber sodium colour. On Sun, 22 Jan 2006 15:19:12 -0500, Steve wrote: Hi, I just had a chance to play with a spectrometer. It's just a little cheap one that belongs to my sister-in-law who teaches 4th grade. Naturally, I took a look at my plant lights. I remember being told that all you really need is cool white fluorescents. Of course, being an orchid grower, good enough is never good enough. Some people add warm whites. I don't, but I do add in some Gro-lux wide spectrum tubes. They look very pink so obviously they add in some of the red spectrum missing in cool whites ... or do they? I'm looking through the spectrometer at a cool white and there is a bold bright line in the blue range at about 435 nm, a bright green line at about 535, and a good red line at just over 600. Then I look at the wide spectrum tube, and it looks just the same except there is no red line. Now I'm wondering how the tubes can look pink but have less red that a cool white? I know... there are places on the internet that show a very accurate spectrum for many kinds of light. Maybe that would answer my question if I looked long enough. Of course, I also took a look at my metal halide lights and the HP Sodium light. My comment on the MH is that there certainly is a lot going on in the green part of the spectrum where the light isn't very useful. I couldn't really isolate the HPS bulb because it shares a fixture with another MH bulb. I could unplug the MH but there is a window right next to it with sun streaming in at the moment. After sunset, it might be worth checking the HPS alone. Steve Dave Gillingham ------------------------------------------------------------------------------ To email me remove the .private from my email address. |
#4
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Spectrometer
Dave Gillingham wrote: Steve, with flourescents the line spectra are from the gas within the tube. The first one sounda like neon.... No. Fluorescents use argon, not neon. J. Del Col |
#5
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Spectrometer
Original post:
========== No. Fluorescents use argon, not neon. ========== Fluorescent lights use a variety of inert gases in addition to the mercury and fluorescent phosphors they contain. Argon is common, but neon may also be used, sometimes in an Ar/Ne mixture. James Aldridge, Ph.D. Fort Worth Country Day School Departments of Science & Computer Science ============================================ James Aldridge - Fort Worth, Texas, USA www.JamesAldridge.com - |
#6
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Spectrometer
Oops! Meet you half way, Ray. You're dead right about the excited vapour atoms
emitting uv which causes the phosphor to fluoresce. It's the electrons of the discharge which boot those atoms up to the excited states from which they relax, emitting uv. But still, the lines to which Steve was referring are from the gas discharge, which is incidental to the illumination function of the tube. That comes from the continuous spectrum emitted by the phosphor. On Mon, 23 Jan 2006 18:25:24 -0500, "Ray" wrote: I don't know that I agree with that, Dave. It is my understanding that the energized gas in the tube (typically a small amount of mercury in an inert gas like argon) emits photon energy in the ultraviolet part of the spectrum as the ions "collapse" to a lower energy state. It is the UV that excites the phosphors, and they are solely responsible for the visible light emitted. That phosphor composition is varied to give different spectral " blends." Neon would be a terrible gas to use in a fluorescent light, as the red color of neon emission shows it to be insufficiently energetic for causing anything to fluoresce. Dave Gillingham ------------------------------------------------------------------------------ To email me remove the .private from my email address. |
#7
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Spectrometer
James Aldridge wrote: Original post: ========== No. Fluorescents use argon, not neon. ========== Fluorescent lights use a variety of inert gases in addition to the mercury and fluorescent phosphors they contain. Argon is common, but neon may also be used, sometimes in an Ar/Ne mixture. Argon isn't just "common" it is the overwhelming choice. The Ar/Nemixture is rarely encountered. Some special purpose tubes use krypton, but they are even rarer than the tubes with neon. J. Del Col |
#8
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Spectrometer
Thanks for the discussion, guys. Those few color lines were so bold and bright compared to everything else, I figured those lines were most of the light being emitted. Maybe not. I don't think my sister in law took the spectrometer back yet. If it's still here this weekend, I might look at it again. Steve Dave Gillingham wrote: Oops! Meet you half way, Ray. You're dead right about the excited vapour atoms emitting uv which causes the phosphor to fluoresce. It's the electrons of the discharge which boot those atoms up to the excited states from which they relax, emitting uv. But still, the lines to which Steve was referring are from the gas discharge, which is incidental to the illumination function of the tube. That comes from the continuous spectrum emitted by the phosphor. On Mon, 23 Jan 2006 18:25:24 -0500, "Ray" wrote: I don't know that I agree with that, Dave. It is my understanding that the energized gas in the tube (typically a small amount of mercury in an inert gas like argon) emits photon energy in the ultraviolet part of the spectrum as the ions "collapse" to a lower energy state. It is the UV that excites the phosphors, and they are solely responsible for the visible light emitted. That phosphor composition is varied to give different spectral " blends." Neon would be a terrible gas to use in a fluorescent light, as the red color of neon emission shows it to be insufficiently energetic for causing anything to fluoresce. Dave Gillingham ------------------------------------------------------------------------------ To email me remove the .private from my email address. |
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