I have noticed an annoying new trend. Many of the fancier new cars have what I think are called Xenon lights that are even brighter than bright lights. Whats the deal. I thought that there were standards for things like that. Or do the rich in their fancy cars need brighter lights than the rest of us.
Actually, Handy, Mr. Moorehead is more accurate. Quite a few of the newer upscale automobiles feature little teeny headlights. To make up for what they lack in size, they make up for by increasing the lumens. The only way to get more lumens than halogen (which has been around for several years) is to make a xenon strobe that strobes so fast that you can’t see the gaps between the flashes.
A similar effect is seen in the sodium or mercury lamps used for street lighting. They flash at 120 flashes per second, and appear to be a steady light.
The xenon headlamps on the cars are irritating because they are a brighter point source of illumination than the older, larger headlamps (including halogen). They also produce less light in the red/yellow spectrum and more light in the blue spectrum.
This brings me to my longtime gripe about the auto industry. They could have started years ago to polarize the headlights vertically, and polarize windshields horizontally, thereby completely (or nearly so) eliminating direct light from the headlight blinding an oncoming driver. The light would be easy enough to see once it had reflected off any surface that depolarizes the light (i.e. roadway, tree, pedestrian, deer, you get the picture)that is reflected back at the driver.
This would work even better now that the xenon headlamps are capable of producing ungodly amounts of lumens. Any light loss from traveling through the polarizing filters wouldn’t matter.
“Moderate strength is shown in violence, supreme strength is shown in levity.”~~G.K.Chesterton 1908
The windshield would have to be polarized. I don’t think you can get a polarizing filter that doesn’t absorb a significant amount of light. Something like 80% transmission is what I remember, though I’m sure someone will correct me.
At night, I don’t want to be driving with a tinted windshield.
On a rainy night when headlights don’t reflect off the surfaces well, the first notice you’d have of an approaching car might be its impact against yours.
Oh my, Im not up to par on headlights. Yikes. Halogen already out? Xenon in? Do they have ‘bright’ too?
xe•non "ze-'nan, "ze-\ noun [Gk, neut. of xenos strange] (1898)
: a heavy, colorless, and relatively inert gaseous element that occurs in air as about one part in 20 million by volume and is used esp. in thyratrons and specialized flashtubes — see element table
I agree with Finagle - polarizers are inefficient. In fact, the maximum transmission it can have is 50%, because half the light would have the wrong polarization and would be filtered out (absorbed). In practice, good ones have about 40% transmission, and commercial grade filters are around 30% or less. So if you cover the headlight with one of these, two thirds of the energy would be absorbed by the filter. It’d get pretty hot. You’d also need even brighter lights to begin with.
Also, a polarizer large enough to cover the windshield would cost several hundred dollars. Another problem is that on rainy nights, the wet road may not de-polarize the light enough to be seen.
The Discovery channel was showing some neat ideas for reducing glare though. One was a headlight assembly made up of an array of many lights, pointing in different directions. It automatically illuminates farther when you’re driving fast, and wider and closer when driving slow. It’d even illuminate the right side of the road when you start turning the steering wheel to the right, etc. It may have had a sensor for detecting oncoming traffic and reducing the light in that direction. Another idea was a heads-up display that overlays an infrared image on top of the actual view.
When I suggested polarizing filters, I wasn’t speaking of 100% polarizing filters. There are various amounts of polarization, and quite a bit less than a full polarization would effectively dim the direct glare of an oncoming headlamp.
As far as “windshield sized” polarizing filters, there is already present in safety glass a layer of plastic to keep the glass from shattering upon impact. Since polarized filters are most easily made in plastic, what would be the problem of using partial polarized plastic sheeting in the non-shatter layer of the windshield at the manufacturer?
The polarization doesn’t need to be such that it would cut down appreciably on the total light transfer of the glass. Just enough to partially block the cross polarized light coming directly from the oncoming headlights. Even the polarizing of the headlight beams doesn’t have to be much to effectively reduce the glare directed into a drivers eyes.
“Misers get up early in the morning; and burglars, I am informed, get up the night before.”~~*G.K.Chesterton *
Partial polarizers? OK, let’s think about a 50% polarizer, i.e. a filter that passes 100% of vertically polarized light and 50% of horizontally polarized light, or vice versa. Putting these on the headlight and windshield will reduce the glare of the oncoming car by 50%. However, it would also reduce unpolarized light by 25%. So the contrast (brightness ratio of ‘important stuff’ vs. oncoming headlight) is only increased by 50%. You’d have to do some experiments to see if that is a significant improvement, but I’d guess it isn’t. It’s less than the difference between a 100-watt bulb and a 60-watt bulb. (Possibly much less - I think higher wattage bulbs are higher temperature and thus more efficient)
About the cost of polarizers - I admit I know little about the manufacturing process, but I heard it involves aligning long chain molecules in one direction using an electric field. Sounds like a much more complex process than manufacturing a simple plastic film. I’ve seen something like 2x3 foot sheets sold for over a hundred dollars.
As for the heads-up IR display, the one I saw on TV was a Jaguar prototype. I think the GM solution uses a dashboard mounted monitor, which Jaguar says is less intuitive than their method of overlaying the IR image with the actual view out the windshield.
I imagine you’re talking about the arc-source headlamps we’re seeing on Lincolns and 'Benzes.
Generally, the law stipulates a sixty-watt maximum on automotive headlamps (off-road lamps of greater wattage must be covered while the vehicle is on the road). The law imposes no limit upon the actual light output (measured in lumens)–only on the rated input of energy (measured in watts).
Of course every headlamp you see on the road provides a greater lumenal output than a household 60W incandescent bulb. Over 90% of all headlamps on the road are halogens. In a halogen headlamp, a quartz bulb constrains pressurized halogen gas–iodine, krypton, or xenon–and application of voltage to a tungsten filament causes the filament to heat up (as well as to emit photons). The heat produced by the tungsten filament causes the gas pressure within the bulb to increase, resulting in redeposition of vaporized tungsten upon the filament. The result is brighter and longer-lasting than a household vacuum-bulb (in which the tungsten filament is gradually reduced to the breaking point). Halogen bulbs are not as common as in household use as vacuum bulbs because the pressure that halogen bulbs constrain makes them far more dangerous–they also suffer from related handling issues (fingerprints on halogen bulbs become hot spots where the bulb can overheat and weaken the glass.
Innovations in coating- and reflector technologies (and, to a lesser extent, filament- and gas technologies) continue to increase the specific light output of halogen lamps. Something of a technological revolution created what I guess you’re wondering about: short arc-source headlamps (a lot bluer than halogen, which in turn were a lot whiter than the yellowish lamps which predated them), descended from the longer-arc Osram HMI’s used for lighting movie sets and athletic stadia. These large, filament-free (the light is created by a sustained lightning-like exchange of charge between anode and cathode through an intervening medium of fluorescent gas) sources emit enormous torrents of light at a surprisingly low cost in energy. Their drawbacks, in the context of automotive applications, are many (and are familiar if you’ve ever arrived early to a concert or a basketball game): they take a long time to warm up to sustained intensity, to proper color, and to full brightness (gas temperature below optimum range); the quality of the color changes if the light is left on too long (gas temperature above optimum range); lights won’t restrike, meaning if the power is interrupted–however briefly–they have to cool down before they will light up again.
These drawbacks were addressed by the introduction of xenon as the gaseous medium between electrodes. Xenon arc discharge lamps are create immediate, brilliant light and are longer-lasting (no filament) and more economical (less energy, more light) than conventional halogen lamps. In fact, an arc source creates about 350% of the lumen output of a filament source of a given wattage. I understand that new-generation arc sources called high-intensity discharge lamps (HID’s) are coming out of development as we speak and are supposed to be even brighter. Further down the road is a quartz halogen (filament-source) bulb, trick-coated and xenon-filled, that is still brighter.
I’m confused here. Above, it was mentioned that the light emitted from electrified gas-filled tubes exhibit strobe behavior (paraphrased). Why should Xenon gas in a tube charged by DC current yield a strobe effect?
And: Besides the 60Hz of AC current, is there any other reason why mercury and sodium vapor lamps act as strobes? …as mentioned above. Is it related to the nature of the electrons jumping energy states?
Yes that’s correct. Sorry I wasn’t clear on that point. The surface of water only reflects horizontally polarized light and absorbs most of the vertically polarized light. So with the polarized headlight idea, if the headlight had vertical polarization, it would mostly be absorbed by the water surface and you won’t see it. If it’s horizontal, it would reach your windshield, but without any de-polarization which would happen if the road wasn’t wet. So it would be blocked by your vertically polarized windshield and you still won’t see it.
The xenon headlights are NOT powered by 12 VDC, but by 70-100 Hz high voltage (generated by some trick circuitry in the lighting system).
As for the mercury and sodium lamps acting as strobes, it is because with AC power, the voltage goes to a maximum positive followed by a return to zero and a swing to maximum negative. This is a sinusoidal wave form which is known as Alternating Current. One cycle is an alternation between the positive and the negative voltage.
“Misers get up early in the morning; and burglars, I am informed, get up the night before.”~~*G.K.Chesterton *