In reply to Horace Heffner's message of Wed, 21 Oct 2009 14:07:37 -0800: Hi, [snip] > >On Oct 21, 2009, at 12:54 PM, [email protected] wrote: > >> In reply to Horace Heffner's message of Tue, 20 Oct 2009 18:37:42 >> -0800: >> Hi, >> >> This appears to be the same technology used in CRT TV sets. I >> wonder what the >> energy of the electrons is, and whether or not x-rays are produced? > > >I didn't see any information regarding that. It must be a pretty low >voltage because otherwise the efficiency would be much lower. The >bulbs are supposedly comparable to CFLs in efficiency. Due to the >quantum nature of light, I think any excess energy above that >required to step up the electrons to the energy levels needed would >be wasted, and that should be well under 20 eV.
I considered that, however there is also the possibility that only some of the energy of a fast electron is lost in each collision, allowing a single fast electron to excite multiple atoms. That would still allow reasonable efficiency, even for fast electrons, so I don't think the efficiency argument can be used to decide about the voltage. IOW I'm still curious. >Better to put the >power toward a higher current than any voltage much above the >threshold I think. The advantage over ordinary CRTs is that the >fluorescent time can be much longer - no need for fast phosphors, >fast travel times, or narrow focused beams. In fact, a low voltage >would assist in getting a wide dispersion of the beam due to more >time for mutual Coulomb repulsion of electrons in the beam to occur. Good points. > >I'm very curious as to whether any rare commodities are used in the >bulbs, what is used for an emitter and for phsphors, and thus the >exposure to the Chinese commodities grab. A filament emitter would >be somewhat of an energy hog and reduce bulb life. The bulb life is >supposedly comperable to CFLs as well. I don't understand why LED >supposedly lights take so much power, unless it is for energy >conversion circuitry. I think some of the big new Wal-Mart store LED >lighting installations use a centralized DC power supply, and DC >network, driven by both AC and by photovoltaics, so that may cut down >on energy lost to heat by their LED bulb replacements. I accidentally >left a two AA battery LED flashlight on and was amazed to see it >running just fine about 20 hours later. It did not produce noticeable >heat. Perhaps LED efficiency depends on the colour? Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
