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What gets me are side-lights on cars that flicker. Cars have DC electric systems in the first place. Where did the Audi engineers find 100 Hz to run the LEDs fr
by abainbridge 9y ago
What gets me are side-lights on cars that flicker. Cars have DC electric systems in the first place. Where did the Audi engineers find 100 Hz to run the LEDs from?
I guess there's a switch mode power supply to convert down from 12 V to something lower that the LEDs need. But AFAIK, switch mode power supplies don't switch at 100 Hz.
I'm pretty sure you could show by experiment that flickering car side-lights are distracting. For example, in a situation where you are pulling out of a T junction in the dark, you're less likely to see a motorbike when it is in the same part of your visual field as a car with flickering lights. Particularly when you are moving your head from left to right, as you do when at a T junction.
I'm not sure how to do the experiment though, since using TV screens, monitors or projectors wouldn't work.
- torrent-of-ions 9y agoThat is seriously annoying. Not only do they flicker, they are slightly blue as well. I have mistaken an Audi for an emergency vehicle in my rear view mirror on multiple occasions. I am sure that this is their plan. Such lights should be outlawed.
- Shivetya 9y agoNow I have found that some mirrors on cars and even motorcycles can distort the reflected light to give blue points. combine with polarizing glasses and it becomes even more difficult to find the exact cause. now if viewing straight on without another element to distort the light, like polarized lenses; I would be interested if the reflector built into the headlamp assembly can cause an issue.
- gargravarr 9y agoI've found the colour to be too close to emergency-vehicle blue as well, particularly if the car behind hits a bump and momentarily brings their headlights into my mirrors, it's almost exactly like the flash of emergency lights. I shouldn't have to be second-guessing whether there's an emergency vehicle behind me, I should be following my first instinct which is to ensure I'm not obstructing traffic. Not clearing out of the way for an Audi pulling a tonne to rocket past me.
- KaiserPro 9y agoI suspect its not the PSU, its the PWM for the dimming. compared to actually lowering the voltage/current of a LED/light/other its far simpler and cheaper just to turn it off and on again at varying duty cycles/ frequency.
- mollusk 9y agoCorrect me if I'm wrong, but isn't it just the de facto way of dimming LEDs? Since as opposed to incandescent bulbs, they require certain voltage/current to be lit, if you pass them less, they simply won't emit light.
- eternauta3k 9y agoYou can feed it DC and vary the current, for example by filtering the pwm.
- colanderman 9y agoThey require a certain voltage (to a first approximation). Their light output is (again, to a first approximation) directly proportional to the applied current. PWM control is just a cheap way of reducing the current.
- abainbridge 9y agoGood point. But there's no reason for the PWM to be in the 100 Hz range either. Even the crappest possible microcontroller using timer interrupts could handle 1000 Hz. Hardware PWM peripherals (that can switch at 500 KHz) have been trivially cheap additions to microcontrollers for decades.
- colanderman 9y agoIt's likely not for dimming but for reducing power usage without reducing apparent brightness. See my comment sibling to yours.
- colanderman 9y agoMay not be for dimming. PWM control is used also to reduce the current (and therefore power, and therefore heat) required to achieve a particular apparent brightness. This utilizes the persistence of vision effect. My guess is that, above a certain frequency, persistence of vision no longer applies, and the light is in fact seen simply as being dimmer (which is undesirable in this case). Hence ~100 Hz.
- anon4728 9y agoIt could be a boost converter if the LEDs are in a series¶llel configuration to save money. PROS Higher voltage is great because the conductors can be smaller. CONS Higher voltages need sufficient insulation. Circuit maybe more dangerous after a collision. Long series of components is bad because one component going open-circuit takes out all others on the same string. --- There are also other technologies like LED filaments which appear like a continuous light with less ability to see individual elements.
- dreamlayers 9y agoMany rear car LED lights flicker because their full brightness is used as brake lights, and they are dimmed via pulse width modulation for normal lighting. This is simply a bit cheaper, which is ridiculous on an expensive car. I don't actually see the flicker normally, but when they quickly move accross my visual field I sometimes see a line of dots from the flicker.
- joezydeco 9y agoCadillacs are even worse. I could swear their brake lights run at 20Hz.