^ Thank you. Was wondering how they produced the lower output Daytime Running Lights. (I rarely turn them on.) I assumed they simply used a resistor.
The flasher relay I made for the Expedition switches the 13.8 VDC alternately to each bulb.
A diode I installed in each bulb’s high beam wire prevents the power from going back through the circuit to the other bulb. When the high beams are switched on through the high beam switch, that voltage is closer to 12 VDC due to the forward voltage drop through the 10-amp diodes.
“The flasher relay I made for the Expedition switches the 13.8 VDC alternately to each bulb.”
It must have given you great satisfaction for having constructed a headlight flasher for an emergency vehicle and seeing it working. I know it would for me.
^ Thank you. Done just to $ave money.
My device has a switch which allows lamps to be flashed simultaneously or alternately. (Simultaneously is a greater electrical load shock, (two head lights 130 W., two fog lights 70?W., two 100-Watt lamps in the light bar 200 W. = 400 Watts!) but also better at attracting gaze of the unexpecting eye. It often allows no siren noise pollution.)
But my relay fails to keep the filaments partially energized during the OFF interval for less thermal shock. So, when possible, I turn it off.
One other note on the soectrum of HID lights. The underlying light is essentially a mercury arc lamp, the same basic technology as bluish or greenish mercury vapor streetlights and not too far off fluorescent tubes. All of these are arc lamps using mercury gas. They are kind of clever because they also contain argon gas. Mercury at room temperature is a liquid and to form the plasma through which the arc forms, you need to heat it untilbit forms a gas. The argon in the tube (it IS a little tube) needs a high voltage to form a arc, so the ballast (electronic or conventional) is set to produce a high voltage at first, forming an argon arc. Argon arc lights do produce visible light, just very inefficiently. Researchers realized an argon light wasn’t going to hack it, but add a little liquid mercury and the hot argon will quickly evaporate thr mercury. Gaseous mercury has less resistance than argon, so once a mercury plasma forms between the electrodes, thr mercury is conducting all the electricity. The ballast can cut the volttage substantially (the mercury plasma doesn’t need as high a voltage to maintain an arc. At that point the argon plasma dies off until it is next needed to start the tube. All this is why conbentional fluorescent tubes and mercury vapor streetlights take some time and a bit of flickering to come on, or at least they did before electronic ballasts were improved.
The mercury vapor arc has output like those shown in graphs, but in most uses it isn’t left as is. The light is very cold and spiky, so has lousy color rendering. Think older mercury vapor streetlights, that had a distinct bluish look. More modern ones look more green than blue. That’s because they added fluorescent materials to the glass casing. They absorb some of the unneeded UV and convert it to reddish orange light. The combination of bluish and reddish gives the green color. But it also gives a much brighter bulb with better color rendition and uses no more power. A household fluorescent tube alao has flueorescent materials on the inside of the tube that emit most of the light and UV emitted by the plasma and in turn emit light of several different wavelengths that give the appearance of white. Warm white tubes emit more red, cool white more green (they all emit a lot of green). The old tubes had very uneven output and poor color rendition, but newer tubes use more different fluorescent materials that give a smoother spectrum.
Auto HID headlights are closer to streetlights, with the flurescent materials taking unused UV and emitting various shades of red/yellow/green instead, giving much whiter light without the noticeable blue-violet cast.
LEDs work on an entirely different principle but have some of the same issues. Current white LEDs are based on blue dice (the LED emitter is a known as a die). In the plastic case around each die are placed varioys fluorscent materials that absorb blue light and emit light in the red-green range. A fair amount of blue light is allowed through. The total of all these light colors determines the kind of white you get. Very blue blue-white models are very efficient because they let a lot of the blue light through unchanged, but they tend to have an unattractive color and very poor color rendering. At thr other extreme are warm white models that have a lot of fluerescent materials to absorb most of the blue light and emit it at other wavelengths. Cool white, natural daylight, and other nade up names fall in between. The color temperature is your best indicator. I like 3000K, about like a halogen bulb it is warm enough to look giid indoors with no noticeable blueness. I love LEDs and will be happy when they take over all auto lighting. Thr new Mercedes S-Class has no conventional nbulbs, just thousands of LEDs that should last as long as the car. L
Interesting. Thank you. Had no idea that HID lamps had Hg inside.
Was interesting seeing a YouTube video where the household yellow LED “bulb” was disassembled to reveal BLUE-emitting LEDs.
Will future LED automobile headlights be comprised of multiple color LEDs producing a WHITE light. Or will they try to produce a high power WHITE-emitting LED?
The only car that I am aware of that uses LED headlamps is the Audi R8. Below is a pic of a 2010 Audi R8 headlight set-up showing how the lamps are constructed. In Europe at the time the lamps cost about $5,000 per pair (or was it for each?).
Automotive HID are actually metal-halide lamps, using xenon instead of argon.
Also a mix of metallic iodides or bromides along with mercury to determine color.
I just tried unsuccessfully to find out whether current U.S. D.O.T. regulations allow LED headlamps. Anybody know what the current status of their regulatory approval is? I know there were regulatory delays a few years ago.
@"the same mountainbike" They are optional on several cars and standard on the new S-Class, so definitely legal. The first were introduced a few years ago.
