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Old 08-21-2009, 04:35 AM   #1 (permalink)
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improving mpg's with led taillights?

the prius uses led taillights and gets better mpg's (in part)because of it. so can you install led taillights on say a 2010 corolla s and get better mpg's. how much better can you get from installing led taillights? are there led headlights, and how much would that help?

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Old 08-21-2009, 09:18 AM   #2 (permalink)
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Hi & welcome to EM,

It should make a small difference -- probably way too small to matter. LED headlights would make a bit more of a difference, but still fairly small. The lights are only on part of the time, and they are very low consumption compared to many other things:

Running without A/C makes a large difference. Figuring out how to eliminate the alternator would make a large difference. Making tire pressure and/or aerodynamic improvements will make large differences. And of course your driving techniques can make a large difference.
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Old 08-21-2009, 09:42 AM   #3 (permalink)
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I doubt it would be a quantifiable difference. You would need to switch every light in the car over to LED, but even then, when are all the lights on loading up the alternator? Not very often. Tail lights, 27 watts each. Brake lights, 45 watts each (only when on of course). headlights, 45-55 watts (depending vehicle) low beam, 55-65 watts high beam. Markers, 9-15 watts each (4 of them on most vehicles). Turn markers, assuming front and rear, 27 watts each, for 4 of them.

So say, 4 turn markers, 4 9W side markers, 2 tail lights, 2 headlights (55W seems more common these days). That's a healthy 308 Watts at approximately 14 volts. But we can do much for the headlights. So ditch that, 110 watts.

So, 198 watts to power the exterior lighting, excluding the headlights. that's around 14 amps draw on the alternator.

Lets swap to LED lighting. Ballparking this, as it would take a while to track down the specific bulbs your car uses, lets assume the 27w replacements use 110mA at our 14 volts. That's roughly 1.5 watts. Soo... high figure it, 2 watts x the 6 27 watt bulbs.

12 watts. Sooo..we removed 5.5 bulbs by switching to LED. Good start. 4 more to go. the 9 watters are 1/3 the power draw, so carry that over, We get 2 watts for all 4. Seems ridiculous to me, so we'll bump it to 4 watts.

Woohoo! Shooting from the hip, generalizing, and using fuzzy math, we have under 20 watts of LEDs compared to 200 watts of incandescent. Even if I'm 100% off on the power draw, that's still only 40 watts.

Okay, we've reduced the load. Now a new problem. The alternator is designed for a certain peak output. It's most efficient at some percentage of that. We're now going way below that. We're now wasting the efficiency of the alternator. We need a smaller one to keep it high. Hmm. Switching to LEDs to save fuel has now cost a ton, for all the LED bulbs to a smaller power supply for higher efficiency. Are you saving money, or just fuel money?

Hope I gave you something to think about. If someone wants to give specifics, go for it. I just generalized power transmission based on the same concepts of the 80+ PSU group for computers. Will swapping all lighting to LED make a significant difference? maybe. But I think changing HOW you drive makes a bigger difference than the design of what you drive. Save the money from the LEDs and use it burning fuel learning how best to drive your car. When you've reached the pinnacle of your efficiency, then start mods to the car's efficiency.
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Old 08-21-2009, 12:50 PM   #4 (permalink)
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According to my scanguage, When I'm idling with a hot engine & I turn on my headlights fuel consumption goes from .31gph to .36gph. 14% at idle. Going down the road at 1.8 gph that's 2.2%. Yes there will be a difference. Will you ever make up the cost, maybe. If they are common bulbs you may be able to transfer them to another vehicle.

I would start by replacing the bulbs that are on the most, especially if you have daytime running lights.

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Old 08-21-2009, 01:36 PM   #5 (permalink)
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One thing to also take in to account is Led's have faster response time, which means when you slam on the brakes because some idiot turned in front of you, the car about to rear end you knows sooner. So they have a +1 for safety in my book.
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Old 08-21-2009, 01:51 PM   #6 (permalink)
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But how much $$$$ do they cost?
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Old 08-21-2009, 02:00 PM   #7 (permalink)
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Originally Posted by KJSatz View Post
But how much $$$$ do they cost?
I've heard that for a full replacement, it's maybe $100 to $130. That doesn't include the headlights because no one has made a "strong enough" (or affordable enough?) LED headlight.

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Old 08-21-2009, 02:04 PM   #8 (permalink)
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SuperBrightLeds.com has a bunch of drop in replacements for cars. They range from $1.29-$22.95 depending on how bright you want them and what bulb you are replacing.
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Old 08-21-2009, 02:31 PM   #9 (permalink)
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Something to be aware of with regards to LED bulbs is that there can some issues with dual intensity bulbs and how noticeable the changes are.

For example, most cars have brake light bulbs that when the lights are on, turn on at low intensity and flash at a higher intensity.

Since LEDs really only have 1 brightness level, this has to be given a workaround where at low intensity, only some of the LEDs are lit and at high intensity, all of them are lit. If the difference between low and hi intensity isnt very significant, or the effect is muted by way of tallight lenses, it can be hard for the cars behind you to tell if youve appled your brakes or not. This same effect can also be a possibility when talking aobut side marker lights that also act as turn signals.

I dont have 1st hand experience with this, but I know poeple who do and felt uncomfortable enough to switch back to traditional bulbs.
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Old 11-08-2009, 11:00 PM   #10 (permalink)
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Quote:
I would start by replacing the bulbs that are on the most, especially if you have daytime running lights.
if you want to ditch your daytime running lights, they should be on a separate fuse. just pull the fuse, and no more DTLs running off your alternator.

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