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The High Pressure Sodium Lamp (HPS)

Here we have another interesting light source its high pressure sodium its a light source that s commonly use today for street and lightning large areas pretty much everybody is pretty familiar with it now because of its orangish glow some of the newer lamps has pinkish or purplish color but pretty much has an orange color. This lamp was actually developed at GE, the ceramic was developed right in Niskayuna, around 1958 and the first lamps And the first lamps which I have a prototype of it was actually built here in Schenectady and they started to experiment with this lamp around 1959 they start to make a lamp with lucalox ceramic and what it is is a ceramic is a polycrystalline aluminum oxide ceramic basically its aluminum oxide is what it is, made in to a ceramic and the reason why they use it in high pressure sodium is because the high temperatures at which this lamps operate quartz or glass or even ceramic ordinary ceramic could not withstand the heat, so they have to make a special aluminum oxide ceramic to withstand the heat that the lamps generate. Basically all the lamp is a discharge lamp, has one electrode at each end at the arc tube and the current goes thru a gas to fill gas inside the xenon gas and is an amalgam of mercury and sodium in the arc tube the reason why there is the mercury and sodium is for two reasons: number one it controls the vaporization rate of the sodium during the warm up, number two, mercury vapor lens it’s blue rays to the light to make the light less monochromatic is more full spectrum because it got blue rays as well as yellow and red and orange rays so is technically a white light source even know it doesn’t look like white. it is a type of white light source. Objects lighted by it at least you can tell the color of them not that well but you can so that’s was the advantage of high pressure sodium design plus they are more compact and longer lasting that the old low pressure sodium lamps were. though they are not that efficient as low pressure sodium but the advantages out way the disadvantages obviously. There are interesting lamp it that to start the lamp when is cold they have to pulse it with a high voltage pulse. to start the arc thru the lamp so to do that they use an external electronic circuit built in to the ballast to start the lamp that work almost like a coil on a car how it fire’s a spark plug it just hits the lamp with a high voltage spike and that s what s start s the arc. Once the arc starts is thru xenon first so the lamp will light up almost a sky blue color then it turn s blue because the mercury vapor the mercury rather vaporizes first then when the mercury generates enough heat the sodium vaporizes last and then the color all finally shift over to orangish color as the sodium vaporizes in to the mercury arc stream and the true colors combine the blue and the orange combine and then you get that purplish orange or whatever color the lamps varies by brand by color so they are not all exactly the same but the lamp has pretty good efficiency it didn’t turn out to be as high efficiency as they originally thought the lamp itself is very efficient but the auxiliary equipment used with it the ballast have to be very lossy because the arcs run at low voltage so they got to step that voltage down in the ballast Here’s another high pressure sodium lamp but this one has a little bit different design is actually a kind of a home owner brand name like for the average consumer Lights of America and they did things a little differently instead of using an electronic circuit to pulse the lamp to start it like as they previously said this lamp has and you can see it there running along the arc tube there’s a flat strip then there’s a little wire that runs down along side the arc tube. And what that does is it just set’s up a capacitance or a stray voltage between the arc tube and the other side of the circuit the return side of the circuit so that the amount of voltage it takes to strike the arc thru the lamp is lower and it doesn’t require a pulse to start it in fact the fill gas in the arc tube may be different to and maybe neon or argon instead of xenon which strikes at a lower voltage so you combined that with the starting strip and the lamp doesn’t require an external lamp igniter it will start on a voltage set the ballast puts out this was used for the Lights of America homeowner light fixture which makes fining replacement lamps difficult unfortunately but they do make larger versions of this lamp to retrofit in to existing mercury vapor fixtures it uses the same basic principle as this and it will start and operate on mercury vapor ballast without any external starting gear being necessary to be added to the fixture in fact one type this strip is actually a heater and there’s a starter in it like a florescent lamp uses that blinks the current on and off to the heater and it gains heat each time until heats up the arc tube and off and that helps it to strike plus every time the starter opens it creates a pulse from the ballast by the induction of the ballast and that helps start the lamp. so, some of the HPS conversion lamps to convert existing older fixtures uses this principle as well. this is just another way to start an HPS lamp without having igniter on a ballast it works ok but it has its issues to like sometimes the lamp don’t like to start on cold weather and things like that, so is not perfect but it is another way to start an HPS lamp

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