billw@dirt.cisco.com (William ) (03/08/91)
Suddenly, there are "Neon light" appliances all over. I rather suspect that these aren't real Neon tubes, unless rapid advances in high voltage technology (and safety) have been made. So what are they? Flouresents with funny colored phosphors? Thanks BillW
charless@cory.Berkeley.EDU (Charles R. Sullivan) (03/11/91)
In article <BILLW.91Mar8025502@dirt.cisco.com> billw@dirt.cisco.com (William ) writes: >Suddenly, there are "Neon light" appliances all over. I rather suspect >that these aren't real Neon tubes, unless rapid advances in high voltage >technology (and safety) have been made. So what are they? Flouresents >with funny colored phosphors? > >Thanks >BillW Actually, most so-called neon signs are not real neon, but just cold-cathode fluorescents with different color phosphors. A *real* neon sign is an orange-red color, with clear glass tubing. When it is off you can't see any color at all. Sometimes they use red tinted glass with neon to get a red color. But pretty much any other color is made by using a mercury-argon gas (instead of neon) and coating the inside of the glass with a phosphor that glows the right color when the UV from the mercury hits it. The phosphor will look white or the color of the light when the current is off, and is pretty much opaque. The high voltage requirements of neon lamps are due mainly to the higher voltage drop at a cold cathode as compared with the heated filament of a normal fluorescent, and the long tubing used in signs that curl around many times. (One of the reasons for using long tubes is so that the power and voltage lost at the cathode won't be too large a fraction of the total input. Voltage drop is on the order of 300V at the electrodes, and 100V/foot of tubing.) Tube diameter, fill pressure and fill gas also affect voltage requirements, but the C-C fluorescent needs similar voltage to a neon. I think a lot of the new stuff like phones with built-in lights has electronics and high-frequency tranformers producing the high voltage. Most, but not all, that I have seen use use C-C fluorescent, not neon. Charlie Sullivan charless@cory.berkeley.edu