It is definitely a smoother output curve than most. Heated filament tends to create a much more stable output. If you look at the curves for the fluorescent you see great instability, which is what causes eye fatigue. If you look at the sodium lamp outputs, which are the new low-energy-use streetlamps and security lamps, you’ll see why they appear pinkish yellow.
I’m getting a bit off track here, but you’ll also notice the word “mercury” in the fluorescent lamps. There’s a great research paper published in the March issue (volume 12) of Environmental Forensics entitled “Mercury in Natural Waters”. It’s deeply researched and highly technical, but it addresses the issues of mercury contamination and its effects. If you can get to it and work your way through it, it’s engrossing stuff.
The graph of radiation from a tungsten filament given in a previous post appears to be the short wavelength side of a filament at about 3000 K.
Below are black body radiation graphs at various temperatures. The left side of the lowest graph (red) appears to approximate the tungsten graph shown in the previous post.
Note that 1 µm = 1000 nm.
Also note that most of the total radiation emitted (area under the curve) is in the infrared.
Nice work, mechaniker. We were actually focused on the visual spectrum and the differences between the curves in the visual spectrum of tungsten filament and HID lamps, but it’s great work anyway. I was attempting to describe why HID lamps appear blue, and touched on the different refractive indexes of different frequencies to explain the blue halo effect, without getting any deeper than necessary for explanation.
And I never could figure out how to post equations. I’m not much of a computer guy.
Halogen lights are actually incandescent lamps. The tungsten filament is heated, glows, and gives off light. Hence its spectrum is continuous and resembles the classic black body spectrum. Its only difference from an ordinary incandescent lamp is that it runs at a higher temperature, and therefore its spectrum is shifted toward the blue.
Because its spectrum is continuous, halogen lights give better color rendition than CFLs.
A short tutorial on halogen lamps is given below. Notice the halogen regenerative cycle, wherein halogen ions (bromine, iodine) capture tungsten atoms emitted from the filiment and redeposit them back onto the filament from which they came.
On the other hand, metal halide (or HID) lights are electric arc lamps. An electric arc is struck between two tungsten electrodes, and the arc energizes a vaporized metal halide gas that emits the light. The color of the lamps is determined by the metal halides used and the temperature of the lamp.
Because the light originates in a gas discharge, its spectrum is spiky as in a CFL, rather than continues. However the spikes can be broadened if the gas is highly compressed, and the gas is often compressed to several hundred psi in metal halide (HID) lamps.
Below is a short tutorial on metal halide lighting,
Correct, and they’re called “quartz halogen” because the bulb is fused quartz. Fused quartz is SiO2, as is regular glass, but is much more pure than regular glass bulbs and can thus withstand higher temperatures. Not as pure as fused silica, but it works for the bulbs.
High Intensity Discharge (HID lamps are, as you said, arc lamps. As I and you both commented, because the light energy is created by constant discharges (arcs) the output is “busy” or “noisy” relative to the stable output of an incandescent lamp.
However this is all going astray of the OP’s original question about the color of headlights. I like to try to simplify things when explaining them under the assumption that the questioner doesn’t already possess a good grounding in physics. And my days of tossing formulas around are pretty much past, and it’s just as well. Formulas are an absolute necessity when working with the technology, but simplicity works best for explanatory purposes.
Thanks.
By the way, I just this afternoon discovered one of my Silverstar Ultra lamps burned out. They’re going for $50/pair now before my veteran’s discount. I replace headlights in pairs, 'cause I know the manufacturing process is highly controlled and consistent (I’ve worked with the Osram people in Manchester and toured their manufacturing floor at Hillsboro where they make headlights), and I figure their lifespan is pretty consistent… if one lamp goes, the other is probably going really soon. Great lamps, but big bucks.
True. I only pointed it out because earlier in the thread someone mentioned the high cost of the Silverstar Ultra lamps. That God I don’t have HID lamps.
I remember with nostalgia paying $3 for my old round sealed beam lamps on my old pickup. Sigh.
Thank you, Mechaniker, for your interesting posts.
Interesting how they sacrifice filament life to increase Color Temperature.
Presumably thinner filament wire so it burns hotter and burns out faster but does not exceed allowable lumens.
That has always been the story with incandescent bulbs of any sort: Run them at slightly higher voltage than rated, and they will burn much brighter, bluer, but have a very short life; run them at a slightly lower voltage than rated, and they will burn almost forever, but dimmer and more yellow.
just this afternoon discovered one of my Silverstar Ultra lamps burned out.
You must wait until the still-lighting lamp burns out to learn how consistant they are!
During emergeny transports, when no traffic is in lane 1, I turn the headlight wig-wag off to reduce filament shock and lessen bulb life reduction.
Even worse, when driving at night, the high beam filaments are alternately lighting in addition to the low beam filaments burning steadily. I wonder what damage that does to the dual-filament assemblies.
Point well made, Robert. To me replacing both when one dies is like cheap insurance. My experience has been that the second burns out pretty soon after the first, and I get anxiety attacks trying to drive a one-eyed car. Maybe that’s a good side effect of having had cataracts. I like to make sure I have plenty of good light.
Good prices, mechaniker. I just couldn’t wait. The moment I realized a light was out, I drove straight to the nearest parts store. Replaced the burned out one in the in store parking lot and the other when I got home. I’m a “crazy man” when it comes to this stuff. I got the Ultras.
One winter evening I was taking blood STAT to a mountain hospital in a snowstorm when the falling snow revealed that the right headlight was out.
I called our local AutoZone, already stored in the cell phone, and asked them for the number of the AutoZone in the small mountain town I would soon be passing through.
The mountain store kindly looked up and pulled the SilverStar™ bulbs for the Toyota I was driving.
5 minutes before closing I arrived, paid for the bulbs, borrowed their flashlight and replaced the burned-out bulb with snow collecting on my clothes and hair.
Then immediately continued on the remaining 80 miles to the hospital.
(Thought I would not be able to get back home that night, but with difficulty managed to return in the deeping snow.)
I waited until the left bulb burned out to replace it. Forgot how many burning hours later it was.
^ During emergency transports at night, the low beam filaments are on steadily as the high beam filaments are alternately flashing at full voltage by the wig-wag flasher relay.
So I wonder how much damage is being done when BOTH filaments are burning.
“During emergency transports at night, the low beam filaments are on steadily as the high beam filaments are alternately flashed at full voltage by the wig-wag flasher relay.”
I see, you are driving an emergency vehicle with flashing high beam headlights. I thought you were referring to pulse width modulation of the high beams to provide daytime running lights. That modulation only occurs when the low beams are off, and the modulation rate is 100 Hz or greater, so in that case I don’t thing the high beam filaments physically vibrate too much.
But you are referring to a high beam modulation of about 1 Hz I assume. So yes, I guess the filaments could be flexed at that rate. Good question; I don’t know the answer.
