LED lighting make a vehicle more fuel efficient?

I was watching a YouTube video produced by the Community College of Philadelphia. In the video, the auto shop instructor is discussing the many benefits of LED lighting, and he makes the claim -

“The amount of electricity that a car consumes actually cuts back on its fuel economy, so by making the lighting more effiecient in the cars, we’re actually raising the fuel economy because the lights draw less power.”

If you're interested, here's the video: https://www.youtube.com/watch?v=jwh2RF36MuM&index=19&list=PLFpeJmmJA1P9brqWaMKPjSw1xgJtHCSXj and he makes this statement about 23:00 minutes into the video.

My simple question is this - is he right or just plain wrong??? Is the amount of electricity a vehicle draws directly related to its fuel economy?



Ed

 

Ehhh...my instinct says no. If you're at idle, for example, your engine is still running at a consistent RPM, burning a consistent amount of fuel and spinning the alternator at a consistent rate, producing a consistent flow of electricity. Changing the electrical demands by switching to LEDs doesn't change your RPMs, so while you're technically using less power to whatever lights you switched out the power is still being produced and likely dissipated elsewhere.
The only way it would be noticeable is if you were drawing a bunch of power with aftermarket lights, so much that they wouldn't even work properly at idle. By switching to LED you would be drawing less power putting the alternator back in a functional range at 800RPM or whatever your idle is.

That all sounds legit but I've never taken a shop class so its just personal experience. If someone posts after me with proof that LEDs will improve my MPG I know what I'm doing today...

 

I've been told multiple times that electrical load does have an impact on fuel usage. It never made sense to me...

 

hes right, however, i doubt you would notice a difference.

 

more electrical load causes more drag from the alternator thus causing the engine to work harder.

 

There is no such thing as a free lunch, so the electricity has to come from somewhere.

LEDs will help with fuel economy. Though it might only be 0.2 mpg heh heh. More electrical load doesn't always mean the rpms go up. Like when I use my ultra gauge, say I'm going up a hill at 1500rpms, engine load is 50%, then I floor it, my rpms won't go up right away but my engine load just went to 90%.

He isn't wrong, but if he was trying to sell me some LEDs and using that as part of the sales pitch.... It's a little misleading.

 

I see...learn something new every day!

 

mutilatedjak is correct, power has to come from somewhere.

Lets take the example of 1 taillight.

1157 LED, white: $25/ea, 235mA, 30K hours.
1157 Incandescent, white: $2.50/ea, 2.10A, 1.2K hours.

The LED bulb only uses 1/10th of the power as the incandescent bulb. At the alternator, that's a difference of about 22W, or 0.03 horsepower per bulb. It's kind of hard to characterize the effect that 0.03 HP has on your total fuel economy, but lets say you spend most of your time cruising at highway speed, and it takes you 30HP to maintain that speed, and you get 20MPG while doing so. If we make the handwaving assumption that there's a localized linear relationship between load and fuel consumption at this point, that LED bulb will save you 0.1% in your fuel mileage, so a 0.02 MPG improvement per bulb. That's a finite improvement, but not really much of one.

And even thought the longer life does seem to justify the cost regardless of fuel savings, you likely won't ever get a return on that either. A typical Tacoma probably lasts between 5000-8000 hours, so there's not really a point in having a bulb that lasts 30K hours.

 

Sounds like a great question to send to the Mythbusters .

Less load on the charging system for sure . Swapped all my lights inside and outside to LED .
Have I noticed an increase in fuel economy ? No because the swap to led was a slow gradual approach reasearching the best bulbs for each swap I performed .
A good test for the Mythbusters who can do a before and after comparison on the track . http://www.tv.com/shows/mythbusters/
Ask them to do the test .
When I changed out all the bulbs in the house to LED , it saved about $30 bucks/ month on hydro . If you factor in the higher cost of the house re-lamp using the newer LED bulbs , its still going to take me a while to recover my costs for swapping to Leds . I sold all my compact flourescent bulbs as they were still functioning

 

Awesome post putting empirical numbers/math into the convo.

This post reminds me of wanting to see what MPG an adruino could muster up if used to make our alternator a "smart" alternator and only charge when in certain engine load/driving conditions. Probably another negligible result, but I have a mini just sitting here...