|High-Pressure Sodium lamps. A good thing gone bad.
And more...about streetlights to nightlights!
|High-Pressure Sodium (HPS) lamps are the source of the golden-orange light emanating from streelight fixtures across the U.S. While the golden glow is seen as romantic by some, the energy efficiency of these lights is their most important characteristic.
In use for several decades, first in big cities, industry, and even on the Golden Gate bridge, their high efficiency brought them to a streetlight near you during the energy crunch of the 80's. In many cases, by government mandate.
Before they were commonplace, I ordered and installed a full-fledged 400 watt HPS streetlight fixture for my rural yard. It was easy to give directions to anyone coming over after dark, "just look for the big orange glow". It was the only one around.
Back when I bought the light, I had a hard time getting over the 60-some dollar cost of the bulb itself. But it was rated to last 24,000 hours or more. So if it was to be lit up about 10 hours per night on average, the bulb should last 2400 days, or about 6 and 2/3 years. To my surprise, the bulb lasted about 10 years! I replaced the bulb, with the new one costing about $40.00. That second bulb lasted about 7 years, not too bad.
When that the bulb burned out, I decided I didn't really need a 400 watt light on all night, so I installed another HPS fixture, this one a 150 watt unit. I put a used bulb that a friend gave me in this fixture. I also replaced the bulb in the 400 watt fixture, which by this time had come down in price to $25.00, and hooked it up to a switch so I could use it only when needed.
That was about 10 years ago. The 150 watt used bulb is still going strong. But the new 400 watt one, which is seldom used, died after a couple years.
My line of work also got me into maintaining some parking lot lighting at a few businesses. And the trend seems to continue. No matter what brand of bulbs or how new or old the fixture is, they seem to last about 1-1/2 to 2 years.
2 years at 10 hours per night adds up to 7300 hours. But the bulbs still claim to be rated for 24000+ hours?? At one time, this was called FALSE ADVERTISING! So the price came down to 1/3 of what it was, but the actual life of the lamp is less than 1/3 of what it was. What we're accomplishing here, is needlessly filling up our landfills with burned-out light bulbs, that contain hazardous materials such as mercury. Is it true that we don't know how to make anything good anymore?
I see the same holds true of the tax-dollar supported street lights, just about as many of them are not working as are. And I think they change all the bulbs in them every-other year or so. But I won't complain too loud, they could do away with half of them anyway, and no one would notice.
The private sector seems to be getting fed up with the reliability of HPS lights, and going more to Metal Halide lamps. They've been around longer than HPS, and offer a nicer, whiter colored light. But they are not as energy-efficient, and don't have the greatest life either.
ADDED 1/15/08; With the cost of electricity rising so the utility big-wigs can afford to put gas in their Hummers, I decided that 150 watts was too much now. I bought an old-time looking farm-yard type fixture that has a 14 inch painted steel reflector that looks sort of like an upside-down mixing bowl. It has a porcelain socket meant for a regular light bulb, and an aluminum fitting that threads onto a piece of 1/2 inch pipe. NO PLASTIC AT ALL! I mounted this contraption in a tree above the driveway, and put a 42 watt compact flourescent (200 watt equivalent) in it. This is a "cut-off" type fixture, meaning that all the light is reflected downwards where it's useful, instead of lighting up the roof and tree tops. Works great, nice white light, bulb lasted 2+ years (on all night). Only drawback, gets a bit dim when it's cold or windy.
Added 1/15/08: Damned! The bulb manufacturers must have read this site, and decided they better wreck the metal halides too! A few months ago, a new multi-million dollar bridge opened up in De Pere, WI., featuring metal-halide streetlamps. Of the dozen or so times I've crossed it, including the first night it opened, not once has every one of the brand-new lights been lit. I think there's four out right now. Of course it could be because of made-in-China fixtures, fast, easy connectors, aluminum wire, shoddy workmanship, or all of the above!
IN CASE YOU DIDN'T KNOW....When an HPS lamp is reaching the end of it's life, it will cycle on and off. At first, it might remain lit for several hours, then go off for a few minutes. Later, it may only stay lit for a few minutes, then go off for a few minutes. Leaving power applied to the fixture with a weak or burned-out lamp can damage the 'igniter' and 'ballast' in the fixture.
ADDITIONALLY...HPS, Metal Halide, and Mercury Vapor lamps are all called High Intensity Discharge, or HID lamps. Instead of having a metal filament heated to a high temperature by electricity flowing through it, these lamps flow electricity through a "vapor" of one type or another, usually including mercury, contained within a small quartz tube. The mercury gives off a bluish glow, and additives such as sodium (salt) create other colors.
The lamps start out very dim when first turned on, then as the tube warms up and the mercury vaporizes, they come up to full brightness over several minutes. Interestingly, once the bulb is warmed up, if the power is momentarily cut off, the lamp will go off and not restart until it cools down again, usually 1 to 5 minutes. This is why you sometimes see streetlights flash off during a thunderstorm, and they stay off, even though the electricity in the area only flashed off for an instant. It is also the reason that most photo electric cells ("electric eyes") that control outdoor lights have a time-delay built into them. That way a brief flash from lightning or car headlights won't needlesly cause these lamps to go through a cool-down and restart cycle. But a hand-held spotlight aimed at the photocell from a car for a minute or so will do it. More fun if the photocell controls about 50 streetlights at once, on a busy downtown street! (How would I know that??) (Oh, those junk-picking nights.....we called it "twinking" streetlights!)
OK, so I know a few things about photocells. You should too. Of all the materials we have, there are none that "turn on" (let electricity pass through) in the dark, and "turn off" (block the flow of electricity) in the presence of light. They are all just the opposite! To reverse this, photo-cells use a "relay". During the day, light shining on the sensor (usually cadmium-sulfide) causes a small amount of electricity to flow into a coil of wire on the relay. The coil creates magnetism, which pulls a piece of metal towards the coil. The piece of metal is connected to a spring and a switch (called "contacts") and turns the switch to the "off" position. As the sun goes down and less light hits the sensor, less power flows to the coil, and at a certain point, the magnetism becomes weak enough that the spring can pull the metal away from the coil, turning the switch "on". The time-delay models often use a "thermal" relay. Instead of a coil of wire, the electricity from the sensor flows to a small heater. The heater warms up a "bi-metal" strip, which bends according to temperature. (That's how many thermometers work!) The bi-metal strip is connected to a switch similar to the magnetic relay described before. The fact that the metal has to heat up and cool down to operate the switch is what gives the time-delay. More complex versions using silicon sensors and microchips are also available, but in most cases, simpler is better! In any case, the photo-cells consume a small amount of power all day, just to keep the light turned off!
Yeah, yeah, I still know more, and I guess you should too! The small LED and especially the neon (orange glow) nightlights that automatically turn off during the day "to save power" have an interesting feature. The photocell circuit uses more power than the light itself during the day. In other words, IT USES MORE POWER WHEN IT'S OFF, THAN WHEN IT'S ON!! But as long as you are buying them and the government is collecting their tax cut on each one, and on the electricity, I guess that's OK!
Last but not least, as long as we're discussing government and light bulbs and so on, check out <watts>
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