Seeing in the dark

Oct 30th 2009
From Economist.com

Car headlamps that turn night into day

ONE of the most enduring urban myths is how the patent for an ever-lasting light bulb pioneered by a lone inventor was snapped up by a cartel of lighting manufacturers, who promptly secreted it away to protect their hugely profitable replacement business.

The fact is, lots of long-life bulbs have been invented over the years since Thomas Edison borrowed the best from the dozen or so different light-bulb designs patented during the early days of electrification and came up with a winner. Practically all the improvements in terms of life and brightness since then have come from the bulb-makers themselves. One of the most recent was Philips’s incandescent light bulb that lasts for 60,000 hours.

As standalone products, though, few of the new designs have been able to compete—in terms of the inevitable trade-off between performance and price demanded by the marketplace—with the 1,000 hours or so of the tungsten-filament incandescent bulb. Most new bulb designs have either been relegated to specific roles or incorporated into mainstream products. But that all changed when the “twistie” or CFL (compact fluorescent lamp) arrived on the scene a decade ago.

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LEDing the way
With over eight kilowatts of lighting capacity in his home, your correspondent decided three years ago to replace each incandescent light bulb, when it died, with a CFL equivalent. It has been a costly exercise. The average saving is supposed to be around $30 for each incandescent replaced by a CFL, over the latter’s supposed lifetime of 10,000 hours. But such savings quickly vanish if a CFL dies sooner than expected, which earlier ones routinely did.

These premature deaths were usually caused by a failure of the CFL’s electronic ballast. This is a small circuit board in the base of the bulb that uses a rectifier, a capacitor and a pair of transistors to produce a steady, high-frequency voltage that stabilises the current which passes through the mercury vapour in the tube. Excited by the current, the mercury atoms emit ultraviolet light, which bombards the phosphor coating on the inside of the tube. It is the phosphor coating, not the mercury vapour itself, that produces the fluorescence effect—and hence the visible light. The ballast is there simply to reduce the lamp’s start-up time and to eliminate flickering.

Unfortunately, the resonant circuitry in the ballast does not take kindly to having its input voltage varied. That is what happens when a CFL is plugged into a socket with a dimmer attached. Also, switching a CFL on and off repeatedly has a similar effect. No surprise, then, that household lights which are used frequently but briefly will burn CFLs out in hundreds rather than thousands of hours. For that reason, your correspondent has now stopped using them in bathrooms and walk-in closets.

He has also found that CFLs last longer when used upright in a lamp-stand, rather than dangling from a ceiling fixture. The worst place for them seems to be in concealed fittings in the ceiling, where there is little ventilation. While it is true that CFLs generate far less heat than incandescent bulbs (hence their five-fold increase in efficiency), they still get pretty hot. If not ventilated properly, their ballast circuitry can get fried enough to fail.

Still, there is no denying that, on most other counts, CFLs are a far better choice than incandescents. They consume a fifth the juice, generally last five to ten times longer, and now cost only twice as much. Over its lifetime, claims the United States Environmental Protection Agency, a CFL saves 2,000 times its own weight in greenhouse gases.

Having now replaced most of the incandescent lights around his home with CFLs, your correspondent has recently turned his attention to the cars in his garage. When bought seven years ago, the family kidmobile came with what were then state-of-the-art quartz-iodine (halogen) headlamps. Given their specially shaped reflectors, there is not much that can be done to upgrade these. Replacing them with fashionable xenon HID (high-intensity discharge) lamps—blue-glared bulbs used mainly in luxury cars in America, but more widely elsewhere—would require a lot of modification that would, frankly, cost more than the car is worth.

But one of the classic cars on the garage stacker is 37 years old, and the other 22 years old. Both hail from an age when halogen bulbs were a lot wimpier, and came enclosed in round “sealed beams” or plugged into the backs of circular reflectors with glass lenses attached. In both cases, the whole headlamp unit can be removed and replaced with something better.

But what? Modern versions of the xenon discharge lamp—developed originally as a replacement for the carbon-arc lamp used to project films in cinemas—give twice as much light as their halogen equivalents and consume only a third of the energy. Lacking the halogen’s delicate tungsten filament, which slowly evaporates with use until it finally “blows”, xenon discharge lamps are robust enough to last at least the lifetime of the car.

In a sense, HIDs are CFLs for mobile use. The main difference is that instead of relying on low-pressure mercury vapour in a longish twisted tube, the HIDs in headlamps use xenon gas under high pressure in a tough little quartz package. Also, xenon HIDs do not employ phosphor coatings to produce their effect. They get their intense, blue-tinged light direct from the tiny plasma glowing brightly between the lamp’s electrodes.

Because of a car’s skimpy 12-volt electricity supply, HIDs in headlamps require fancier ballasts and voltage-boosting circuitry. The difficult part is getting them to switch on instantly. Though irrelevant for stationary applications, a rapid warm-up time is crucial for cars. It matters little that street lamps fitted with sodium or mercury HIDs can take several minutes to come up to full brightness. Though costlier, xenon allows a discharge lamp to start far more quickly.

But for all its virtues, the harsh blue light of a xenon discharge lamp would look awfully out of place in a classic 1970s or even 1980s sportscar. As a temporary measure, your correspondent has decided instead to upgrade both cars’ headlights with the latest versions of their original halogen bulbs.

Meanwhile, he intends keeping an eye on developments afoot in LED (light-emitting diode) headlamps. Taking their lead from Formula 1 racing—where LED brake lights that come on instantly have long been mandatory—carmakers have embraced LEDs for rear lights, brake lights and daytime-running lights. The tiny diodes give designers greater freedom to come up with interesting lighting shapes. Their instant switching is handy, too.

Now, a few pioneering car firms have started using LEDs in headlamps. Here they are even more efficient that HIDs—and produce light that is the closest thing yet to actual daylight. Those fitted (as a special order) to Audi’s top-of-the-range model cost an additional $5,000. Perhaps one day, such solid-state headlights will be cheap enough to be after-market replacements not only for today’s dazzling HIDs, but also for yesterday’s far fainter halogens. It would be nice to be able to see in the dark as well as the rest of the night-time traffic.

Seeing in the dark
Car headlamps that turn night into day
See articleOct 30th 2009 |

Haryadoon wrote: Nov 2nd 2009 9:25 GMT Twenty comments and a well-researched article, but no mention of light quality. The quality of light from these different technologies varies greatly. I mean the quality in terms of how the human eye deals with it. It's well known that flourescent lights in all forms provide a quality of light that is not ideal for the human eye. Traditional incandescent bulbs are much "easier" on the eyes. For cars, the less efficient halogen or incandescent bulbs are easier on the eyes (of other drivers) than HID technology. Some governments recognise the difference in their regulations, recommending appropriately-bright incandescent bulbs for reading, for example.

Re. blinding oncoming drivers: what ever happened to self-levelling headlamps ? Don't they solve the problem of mis-aligned lamps ?
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Carbon Sink wrote: Nov 2nd 2009 11:44 GMT I bought my very first CFLs 10 years ago specifically for the concealed (and recessed) fittings in the ceiling of my basement because they were cooler (i.e. didn't make the floor above warm). It was a safety consideration. They are still working well!
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Carbon Sink wrote: Nov 2nd 2009 11:47 GMT Pruz wrote: The author has missed one place where HIDs are very useful - on bikes.

HIDs are losing favour to high intensity LEDs for bikes. HIDs are expensive, have a poor quality of light, and most importantly require large batteries to run them for more than a couple of hours. LEDs trump them on all accounts.
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Falmer wrote: Nov 3rd 2009 7:03 GMT And here I'm discovering that being a correspondant for the Economist does not mean living on scraps!
8kw of lightings, even on traditional bulbs at 2x100w per room still implies that being a journalist does not mean passing on the McMansion or the sports car!
Damn, had I known I could have taken the more interesting career choice :D
But, well, The Economist has graced me with an invitation to present my project at its Carbon Economy Summit, so I have to believe this will bid the best for my future and allow me getting to know such a crowd.
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Falmer wrote: Nov 3rd 2009 8:26 GMT And here I'm discovering that being a correspondant for the Economist does not mean living on scraps!
8kw of lightings, even on traditional bulbs at 2x100w per room still implies that being a journalist does not mean passing on the McMansion or the sports car!
Damn, had I known I could have taken the more interesting career choice :D
But, well, The Economist has graced me with an invitation to present my project at its Carbon Economy Summit, so I have to believe this will bid the best for my future and allow me getting to know such a crowd.
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generated3427580 wrote: Nov 3rd 2009 1:27 GMT A fine article but not much info on LED's. Have there been any developments in replacing fluorecent fish-tank lights with LED's for instance?
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willstewart wrote: Nov 3rd 2009 1:58 GMT A PS note for watchingchina - of course RF is not the only kind of wireless power. My watch is described as 'solar powered' but this will mean room-lighting-powered at least in winter. This poses fewer regulatory issues and may make at least as good use of the energy; but may not work so well with higher-efficiency lighting!. Though since the watch includes radio time receivers so it can self-set in most parts of the world it must be highish in the watch power stakes!
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willstewart wrote: Nov 3rd 2009 5:14 GMT Haryadoon
Indeed colour of lights is an issue; flourescents vary but tend to be red-poor and to be degraded by residual narrow-line emissions. LEDs can be better but remember that LEDs may actually be deep blue - white ones use phosphors to get the broad emission as flourescents do, albeit usually better ones. And one can fill in with red (& perhaps green) LEDs to get better colour. All these better-looking lights will be less efficient, too, but still much better than incandescents.
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generated3427974 wrote: Nov 3rd 2009 5:25 GMT The xenon lamps may be better from a lighting standpoint but they are terrible from the standpoint of somebody illuminated by them. The color causes vision blackouts just when you don't need them, driving at night. If these cars were the only car on the road they would be great. As it is they should be baned as accident rates would triple if all cars had these blinding lights.
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Nirvana-bound wrote: Nov 3rd 2009 7:54 GMT Frankly, I won't brush aside the urban myth about the ever/long-lasting bulb patent being avariciously buried by competing bulb manufacturers, as totally far-fetched.

Infact I'm inclined to view that as a distinct possibility, knowing how greed & the bottomline, always prevail over progress & humaneness, in the selfish, self-absorbed & psychopathic corporate world.

Still, I look forward to the day when LED lights become 'standard' on all new cars.
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billwald wrote: Nov 4th 2009 2:24 GMT For the last 3 years I have been using yellow tinted bifocals round the clock. I wish I had switched to them 30 years ago. They take the sharp glare from head lamps at night and the tint isn't bothersome during the day inside or outside.

Fluorescent bulbs last much longer if one never turns them off. I have a standard 18 watt unit in my kitchen which is always on and has been replaced twice in 15 years.
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Black Eagle wrote: Nov 4th 2009 6:55 GMT Well Written.. NOT! When I was a child, visiting the former Sarasota Florida home and laboratory of the late Thomas Edison, at the local Fire Department there was a single bulb which had been installed by Edison, burning 24-7-365 since his death in the 1930s. That was 1960, approximately, so that bulb lasted for 30 years! The principle to do this, I subsequently learned, is simple. thicker filaments and removal of ALL -- and not just part -- of the oxygen in the bulb, which otherwise oxidizes the filament causing it to burn out. This is not rocket science, and "long life" bulbs often play games with such parameters, the bulb companies knowing full well they could produce a 30-year bulb tomorrow if they wanted. As to CFLs, of course they are a nightmare -- ugly light, emission of irritating EM and RF, toxic when broken, and actually short-lived if you turn them on and off frequently, as human beings tend to do, unlike laboratory tests. I will buy cases of old-style incandescents in the USA, to stock up for what we call the "Impending Obama Socialism", and will wait for the development of full-spectrum LEDs. Beware of "scientists" or "journalists" trying to lead you around like cattle into the pen.
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Amir Akeel wrote: Nov 4th 2009 5:01 GMT LEDs in Headlamps? Not Likely!

At least not yet.

If you want to see the future head to any American military base. LEDs have already replaced the old fashioned sealed headlamp units that have been the mainstay of American tactical vehicles for decades. The LEDs certainly are bright...and blue. In fact too bright and too blue. The headlamps used by the US contain several LEDs in a ring around the lamp's center. Unfortunately, due to the many light sources and shape of the reflector, the light is thrown out in all directions and tends to blind oncoming traffic. In other words, LEDs can't throw light out as far as a focused halogen or HID can. Add to this the fact that LEDs generate most of their light as an uncomfortable bluish hue (even more annoying then HIDs) and I would say we are at least 5-10 years away from a good LED headlamp.