light color,auto vs photo lighting

maybe DS can answer this - - what's the problem w/ headlights being bluish, and they used to be yellowish,when studio lighting for photographers has been at fixed
color temperatures for a long time? why can't headlights be made at fixed color temperatures like studio lighting? why this hassle of being a silly blue tint? Tom Seattle
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I Love Edsels wrote:

I'm not Daniel, but I would guess there's that silly little problem with efficiency. I'd suppose that being plugged into a wall outlet and having oodles of power to work with helps if you have a desired outcome with filters.
Headlights have to (legally) run on 55/65W, and I believe the inherent output of a halogen-filled, tungsten filiment bulb is slightly yellow. Then there's HID, which DS has said could be of a similar color if they really wanted it to be. I've read that the the xenon gas in HIDs (to help with quicker startup) does tend to glow slightly blue though. Still - the color of current HID setups is supposed to be designed for "The Look" of something different than ordinary lighting.
In a studio setting, I suppose the inefficiency of a filter can be overcome with a brighter light source.
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On Mon, 16 Jan 2006, y_p_w wrote:

No, if the lamp is run at its rated voltage, it's white. A continuous-line spectral power distribution with a Colour Rendering Index (CRI) in the high 90s.

Also white, but a discontinous-line SPD with high spikes in the violet, blue and blue-green and a CRI in the mid 70s.

Yes, it does. You'll also notice that some HID car headlights appear much bluer than others. This is an optical effect, and there are entire websites devoted to photo essays on how to make your HID headlamps look bluer.
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Never mind that there are a couple of us here and there who think that your (generic "your" - not aimed at you, Dan. I know you already know better!) blue headlights would look coolest after being hammered, rocked, bashed, smashed, shot, or otherwise rendered permanently dark.
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On Sun, 15 Jan 2006, Don Bruder wrote:

There are also automotive HID lamps ("bulbs") made by major makers, specifically designed and manufactured to filter out most of the blue. They certainly do that; the headlamp light when using one of these is selective yellow. Of course, if the maker of a particular lamp has twiddled the optics' geometry to produce a strong blue glint at the low beam cutoff, that cutoff will now appear green...
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Blue, green, orange with purple pinstripes... The color isn't the issue for me. What IS the issue is the friggin' wash of glare that *EVERY* "blue-headlights" vehicle I've ever faced puts out.
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Daniel J. Stern wrote:

The vast majority of halogen bulbs I've seen on the road seem to tend towards slightly yellow at most viewing angles. The Narva Rangepower +50 I got from you seem a little less so. Same for the 9006 GE Nighthawks I put in my folks' Camry.

Well - I live in a hilly area with many winding streets. I've seen real HIDs, and from certain angles, some have looked purple or blue and then look closer to white as I approach. The "HID-like" bulbs don't seem to have that effect.
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Daniel J. Stern wrote in part:

Tungsten lamps are defined by the definition of CRI to achieve 100.
If the color temperature or correlated color temperature is in the mid or lower 3,000's, then the color would widely be seen as a yellowish or orangish "off-white". If the color temperature or correlated color temperature is in the 2,000's, then the color is even more orange-yellow or yellow-orange, although ideally an orange-yellowish white to whitish yelow-orange. Tungsten filament lamps are normally designed to have color temperature somewhere in the 2,000's to mid-3,000's Kelvin, usually at least mid-2,000's and usually at most not much above 3400.
But by definition tungsten incandescent lamps have a color rendering index of 100, as well as daylight - even blue sky even when achieving a somewhat blue shade more of a whitish blue than bluish white, like 25,000 Kelvin. (Blue sky has been noted to sometimes achieve color close to that of infinity color temperature - which has CIE-1931 chromaticity coordinates of about x=.240 y=.234, a fairly whitish blue).
Light reasonably achievable by tungsten lamps is defined to have a CRI of 100. So are reasonable shades of sunlight/daylight more blue (less orange-yellow) than usual achievable by tungsten-incandescent.
- Don Klipstein ( snipped-for-privacy@misty.com)
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On Mon, 16 Jan 2006, Don Klipstein wrote:

Of course they are. But I was including all the factors that go into the SPD of the light emitted from the headlamps of a typical vehicle in use, including the CMA quotient! ;-)
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I Love Edsels wrote:

Hi Tom,
People have leapt into the technical side, but perhaps could have also answered your question more directly.
In photography, the color temperature and balance required is defined by the film stock you use. I use Fujifilm 50ASA Velvia calibrated for Daylight for exterior photography and its sister film calibrated for Tungsten (3200K) for interiors and detail photography. As a result, when using the latter, I need to light my scene for 3200K if I want white surfaces to appear white when printed, or with daylight balance fluorescents for the former. Hence, the lamps are matched to the film, and there are only a few families of films.
In vehicle headlights, the rendition of light is not nearly so important as its presence, quantity and distrbution - ie, it is helpful if the driver can see the road. As a result, there is limited value in selecting a particular color or quality of light. More important considerations in headlamp design are vibration resistance (essential), lamp life (useful), efficiency (important and increasingly so), initial cost (we care less than the car companies who want to save every cent they can), optical properties (essential for reflector design) and instant start (essential). Ask yourself, do all cars need to look the same?
There is a feeling among car designers now that details like the color and quality of light are a part of the sales features of the car, as they are a significant part of the car's look. This is a newer consideration, and is driving a lot of what is being discussed by the other posters.
I hope that helps,
Thomas.
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Thomas Paterson wrote:

And hence the move towards "HID look" halogen bulbs from even the more reputable manufacturers. It's amazing how many people are convinced by advertising that their "blue" headlights are somehow enhancing their safety because, "HIDs must be blue because blue light is safer".
** **
Half of the Sneetches have bellies with stars, and half of the Sneetches have no stars on thars.
The problem is, all of the Sneetch Dads and Mothers want bellies that look like the ones of the others.
But here comes that sly guy, Sylvester McBean, and his magical Star-On and Star-Off Machine,
Who says "Step right in, I'm the Fix-it-Up Chappie. I'll change all your bellies and then you'll be happy!"
-"The Sneetches and Other Stories" by Dr. Suess
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y_p_w wrote:

Oh - found the DS post on the genesis of why HIDs tend towards blue.
<http://groups.google.com/group/alt.autos.subaru/msg/8f3271925f9f7c33?dmode=source
"When the first automotive HID headlamp was demonstrated by a major European lighting manufacturer to automakers, in the early mid 1990s, it was a very well-designed optic, given the infant state of the art at the time. It handily outperformed most halogen lamps, and of course consumed less power. It was based on modified HPS (high-pressure Sodium) arc chemistry, and had a very similar operating appearance when warmed up to a halogen headlamp.
The automakers reacted favourably to the increased performance and reduced power consumption, but rejected the lamp on the grounds that customers would be unwilling to pay any premium for a lamp that looked the same as the ordinary kind, regardless of increased performance."
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wrote:

This is certainly an interesting story, but is it true? I worked at GE Lighting during the time period they were developing HID auto headlamps and never heard of a headlamp based on HPS technology and never heard any discussion of wanting HID lamps to be "blue" to differentiate them from tungsten lamps. (Though similar issues were certainly discussed in relation to other products.)
As far as I know, the feature that was supposed to make these lamps be worth more money was their higher output (for the fixed amount of power that was allowed to be used) which would in turn enable smaller headlamp reflectors and lower hood lines. Hence the higher amount of spill light.
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these lamps be worth more money was their higher output (for the fixed amount of power that was allowed to be used) which would in turn enable smaller headlamp reflectors and lower hood lines. Hence the higher amount of spill light.
Manufcturers begged to be able to use oblong headlights back in the sixties, arguing that the lower profile, relative to the 7" round headlights proscribed by law, would lower hood lines and decrease wind resistance, increasing MPG. When legislators agreed, and permitted the low-profile oblongs, the stylists' response was to stack them one above the other. Incredible, but true.
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On 16 Jan 2006 20:08:04 -0800, "video guy -

Perhaps the world wasn't ready for low hood lines :-)
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That was the intent of the lamps on the 1993 Lincoln Mark VIII which was the first vehicle equipped with HID by a North American Auto Manufacturer. The higher output and lower hood line possibilities drove initial interest. There was early speculation that the "bluer" color might be better than the "yellow" color of the incandescents for driving, however it's not easy to measure and quantify "better for driving" since that is a highly subjective preference, and the argument still continues. Anyone who has driven a recent OEM HID headlight, will most likely rate it as better performing than any incandescent regardless of how you argue the science.
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On Tue, 17 Jan 2006, Boxman wrote:

Well, sure! The human visual system is a lousy judge of its own performance. All it takes to generate highly favourable subjective ratings of headlamps is high levels of foreground light.
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Victor Roberts wrote:

The way I understood it was that the blue was a result of doping with Xenon, which was added only so that when the lamp was initially turned on there was sufficient light to drive with. An automotive HID lamp typically takes around 3 minutes to come up to full intensity. You can see this when first turning the lamp on the color is extremely blue quickly turning to blue-white.
The biggest advantage of HIDs in the automotive world is power consumed - only 35W compared to 55W to halogen lower beams and 65W for halogen upper beams. And less power consumed means greater gas mileage and/or power drain for electric cars (I think all the electric or hybrid cars I've seen use HID lamps). Plus, you get the greater efficacy (more light for less power). And with today's designs, manufacturers are using the same 35W HID bulb for both lower and upper beams, using a moveable bulb shield to switch between the two functions. This leads to a smaller headlamp design since two cavities are merged into one, but not necessarily smaller reflectors which are extremely inefficient.
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On Tue, 17 Jan 2006 17:33:53 GMT, "Douglas G. Cummins"

I must admit I have not seen a spectral curve of an HID headlamp, but I would be rather surprised if the xenon made any significant contribution to the spectrum when the lamp was fully warmed up. In normal metal halide lamps the mercury output is just about nil when the lamp is hot enough for the metal halides to be vaporized. The energy levels of xenon are higher than Hg so the xenon should have less contribution to the spectrum that the Hg in normal metal halide lamps.

The moveable bulb shield is necessary for reasonable lamp life and performance irrespective of the size issues. If two separate arc tubes were used, or like the two filaments in an incandescent headlamp, or even separate high and low beam lamps, the arc tubes would have to be constantly switched on and off as the driver switched from high to low beam and back again. When GE was working on HID headlamps, some of the staff at Nela Park tried to convince me that people didn't change from high to low beams that often so this would not be a problem. These folks lived in a medium size city and drove either on well lit city streets of divided highways. Perhaps they never used their high beams. I live in a semi-rural area and drive on two-lane roads that have no street lights. On a typical 10 mile trip to the nearest mall, I may switch between high and low beams 10 to 20 times.
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Victor Roberts wrote:

But would you say that adding Xenon increases light output during the initial lamp warmup? The only other HID experience I have is with high output HID lighting like garage or stadium lighting where the light color has much less blue but the warmup time until full intensity is much longer than for automotive HID. I do watch the spectrum of HID headlamp bulbs as they start and warm up. It definitely changes over time until thermal stability sets. Whether it's because of the added Xenon or for another reason I can not say for certain, but that is what I had been told.

Unless the lower beam HID stays on all the time and a halogen lamp in a second cavity is used for upper beam, which is what the first generation of vehicles with HID lamps used, as well as a number of current models. As an aside, this is given as a "legitimate" reason for having blue-tinted halogen bulbs - to have a better color match to the HID lamps in use.
Also, a separate HID upper beam wouldn't work well when on for short durations - a "flash-to-pass" would be ineffective since the startup intensity is lower than its warmed-up intensity.
Another technology that was (or is still being) investigated is using a magnetic field to change the position of the arc-filament, much like a two-filament halogen headlamp bulb, so that the same bulb can be used to provide both lower and upper beam functions. Much more difficult, but it has the advantage of no moving parts to potentially fail.

But if you look at all vehicles as a whole, the majority of nighttime driving is with the lower beam. This is really only an argument against developing a separate HID upper beam, and possibly determining which is more economical - using a switchable bulb shield to create an upper beam from the lower beam cavity or having a second cavity with a halogen bulb for upper beam.
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