Model S Headlight and Tail Light 'beat' frequencies?

[stephenpace]

I took some video of a Model S today at the Houston event, and in watching it when I got home, I realized something about how the lights work (headlights and tail lights, at least the borders). They are not just on or off--they constantly paint just like a TV screen.

1) Is this true of all cars with LEDs?
2) Is the purpose to save power?

I can post a video if I'm not making sense, but it is extremely clear from the video, perhaps because I used a cheap camera. I tried to Google to find the answer and got into pages that discussed beat frequency and Kell factor, but nothing in relationship with car headlights and tail lights.

 

[Doug_G]

That is how you control the brightness of LEDs - you pulse them at a frequency that is too high for the eye to see. The longer the pulse is on, the brighter the LED is. It is much more efficient to do it that way than to burn off power in a resistor.

 

[TEG]

That 'effect' has been discussed a few times on the forum before, including here:
Model S Sneak Peek: Alpha Drives

 

[pete8314]

This reminds me, what's the consensus on the 'safety' brake lights I've seen on a few cars, where they pulse quickly if the car is braking heavily? I've seen no comments on this, so I assume the Model S doesn't currently have this feature, but it seems to me to be a good idea?

 

[jerry33]

This reminds me, what's the consensus on the 'safety' brake lights I've seen on a few cars, where they pulse quickly if the car is braking heavily? I've seen no comments on this, so I assume the Model S doesn't currently have this feature, but it seems to me to be a good idea?

I have no idea what the consensus is but to me it sounds like an answer in search of a problem. If you're driving so close to the car ahead of you that you need extra alerting, it's your driving that needs adjusting. 4 seconds following distance is the correct number.

 

[stephenpace]

@Doug_G: Thanks!

 

[pete8314]

I have no idea what the consensus is but to me it sounds like an answer in search of a problem. If you're driving so close to the car ahead of you that you need extra alerting, it's your driving that needs adjusting. 4 seconds following distance is the correct number.

I don't, but having been rear-ended twice in the last 3 years here in Texas (both uninsured drivers) I'd like to avoid that in my Model S. People drive WAY too close in Texas (compared to what I'm used to in the UK), so just like all the new safety gadgets popping up in news cars (automatic breaking if the car detects the car in front has slowed, and you're not reacting), it all helps

 

[jerry33]

People drive WAY to close in Texas (compared to what I'm used to in the UK)

You got that right. Although I've never driven in the U.K., everyone I know who comes from there comments on how undisciplined the drivers here are. I'll go along with the automatic braking but a surprising number of police cars that have their lights flashing get hit (apparently people fixate on the blinking lights and drive into them), so I'm not convinced blinking brake lights would improve the situation.

 

[brianman]

police cars that have their lights flashing get hit (apparently people fixate on the blinking lights and drive into them), so I'm not convinced blinking brake lights would improve the situation.

I'd love to see a study on this. I've seen 3 collisions in person that were due to "ooh pretty" modern police lights. I feel they've crossed over the line from "get your attention, police vehicle" to "hazardous road distraction". Heck, I'm surprised some of them don't trigger epileptic fits due to the pattern and speed of flickering.

 

[Doug_G]

It's well-known among racers that you tend to drive where you look. It's very useful when the car is in a skid - your hands automatically tend to steer the car to where you are looking, without you having to think about it. The net result is you look at something, the car goes there. You just have to be smart about where you look.

If you look at the bright flashing lights you tend unconsciously to steer in that direction. That's why cop cars are crash magnets.

 

[Robert.Boston]

This reminds me of the 2010 death of the Segway owner (not the inventor)--although it may have been that the trail was too rough, I suspect that Heselden was admiring the vista off the cliff. Wheels follow eyes....

 

[raymond]

1) Is this true of all cars with LEDs?
2) Is the purpose to save power?

1) Yes. This is easily observed when driving behind a car with LED lights and quickly moving your eyes from left to right. You will see a pattern of dots instead of a streak of light.
2) Long, long ago when I played with (low-power) LED's you could save a lot of power by running 10x the normal power through a LED for 2% of the time. It could very well be that this still is the case.