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From regular to LED bulbs – How much of a power savings can you expect?

It’s a well known fact that LED’s require very little power to provide the light of a similar incandescent bulb. In automotive applications, there are situations where reducing the power draw is desired. Switching to LED’s can be helpful here.

In this test, I replaced the “parking lights” in a vehicle with LED’s. “Parking Lights” refer to all the lights that are on when the headlights are on (with the exception of the headlights themselves).

In this case, it included:

  • Front Side-Marker Lights x 2 (194-type bulb)
  • Rear Side-Marker Lights x 2 (194-type bulb)
  • Rear Park Lights x 2 (1157-type bulb)

Replacement bulbs were ordered as follows:

  • 2 x 194 Yellow (4-bulb LED)
  • 2 x 194 Red (4-bulb LED)
  • 2 x 1157 Red (24-bulb LED)

With an ammeter, I measured the current running through each bulb. Here are the results:

Regular BulbLED
194 bulb0.25A0.04-0.05A
1157 bulb0.57A0.04
Total current with all bulbs2.14A0.24-0.28A

As you can see, over 2 amps is pulled by the regular bulbs. Less than 1/8 of that power draw is pulled by the LED’s. Even more shocking is the actual brake circuit of the 1157 bulbs (not listed in the table). Each bulb pulls 2.08A when braking, while the LED’s pull 0.12A. In this case, the regular bulb pulls 17 times as much current as the LED. In all fairness, the 24-bulb 1157 LED’s aren’t quite as bright as the regular bulbs. A 30-bulb 1157 LED would be much more similar, and would probably pull only a tiny bit more current.

Certainly, by replacing regular automotive bulbs with their LED versions, you can reduce the current draw, and help to reduce the load on the alternator (or reduce the current drawn from the batter when you’re running without an alternator). Based on the information I’ve been able to collect, it would seem that the reduction can be anywhere from 1/8 to better than 1/16 of the current draw.

9 Comments

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  1. Do the LED lights have an effect on the flasher circuit? (Flash rate, or other affect)

    • AJ:

      I didn’t replace the signal bulbs, because LED’s are in fact known to wreak havoc with the flash rate. The flashing unit itself expect a certain resistive load (the same load provided by a couple regular automotive bulbs). It would likely either stay full-on, flash at an insanely quick rate, or not flash at all.

      There are 2 known “fixes” for this.

      1) Add resistors (you can actually find resistors on eBay meant to be added to the line when you use LED’s in cars). These provide the resistive load, and you get a normal flash rate. However, it comes with downsides – the resistors themselves have to be spliced into the line, which means you’re cutting wires to put them in. The other downside is that they heat up, which means they’re converting power to heat, which means… you’re not getting any energy savings by using them. So you basically defeat the power savings benefit.

      2) Replace your flasher unit with an electronic one. These can also be found on eBay and start at about $25 if I remember right. Because they’re electronic and don’t depend on the circuit load, they flash at a steady rate. It should in fact be possible to find electronic flashers where you can even *adjust* the flashing rate. They shouldn’t use much power at all, so you keep the power savings benefit. Downsides here though… there are a couple pin variations for flasher units – you have to make sure you get the right one for your vehicle. They’re also more of a pain to install – best-case-scenario you’re crawling under your dash to replace it. Worst-case-install-scenerio you’re pulling stuff apart to get to the flasher. Next downside is that it’s adding cost to your conversion (at least $25). Finally, because they’re electronic and flash at a steady rate, you don’t get any indication if a bulb burns out. Remember in a standard system, if your signal starts flashing quickly you know a bulb is burned out – not so in an electronic flasher because it goes at a steady rate regardless.

      In any case, had I been intent on using LED’s for the signals, I would have gone with the electronic flasher. However, because the signals aren’t on very often (just for a couple seconds when changing lanes, or maybe a minute at a time when sitting at a light making a turn – really of all the bulbs in the car, they’re on the least and therefore benefit the least from LED’s), I decided it wasn’t really worth the extra expense and hassle of putting it in. So regular bulbs for signals and LED’s everywhere else has been the best compromise.

  2. I know it’s been almost 11 years now since this article was written and 7 years for the last comment but I just checked and prices have drastically fallen on the flashers,bulbs offered are brighter but a little more expensive as they are a hot commodity in Northeast Fl. where i’m at. I converted my motorcycle 3 years ago and have not had a failure yet. The norm for m/c bulb replacement could be weekly or at a bad time when you need them. I’m converting my camper month to month and after that the truck.

  3. Akash handa

    Sir i am from india.. Today i installed hazar lights into my motorcycle and a led headlight of 20w..my battery died today itself.. I checked the default headlight of my honda motorcycle which was by Phillips rating of 35w..i dont know what went wrong with the battery.. Please help sir.

    • Best guesses?

      • Alternator/generator died (check by testing voltage at battery terminals when running and make sure it’s higher than the voltage when off)
      • Battery has reached end of life and has failed (check by charging, letting sit for a few hours, test with a volt meter, then load test)
      • Wiring short somewhere (check by having all loads off, motorcycle not running, and use an ammeter to see if current is > 0)

      …if you think it might be related to the LED (ie pulling more than the 20w advertised), I’d hook the bulb up to a DC power source and measure the current to ensure it’s near the advertised wattage. If it’s a 6v system on the motorcycle, you’d be looking for a little over 3 amps at 6v… if it’s a 12v system then under 2 amps. If you don’t have a DC bench supply you could potentially use the motorcycle’s battery, alligator clips, and an ammeter.

      Other option is of course to use trial-and-error + process-of-elimination to eliminate the LED headlight as a cause… use a standard 35W bulb again for a few days – if it works fine, then try switching back to the 20W LED. If the LED always drains the battery there could be an issue with it.

      • Akash handa

        Sir can i install led indicators by replacing the default bulbs of the four bike signal indicators..??
        Because i think that those four bulbs may be consuming more power.. As i use the hazard lights modes to flash flicker etc.

        • It’s usually possible, but keep in mind that common signal flashers often are not designed for LEDs. If that’s the case they may either flash too quickly or not work at all, unless you replace the flashing unit with an electronic (LED-compatible) one.

          Since signals aren’t usually on very frequently though (compared to brakes, headlights, taillights, etc), the overall power savings is usually pretty small, and the expense of possibly changing the flashing unit may not make it worthwhile unless you’re intent on saving every bit of power you can.

          • I have converted my motorbike to led indicators and yes the LED globes are very cheap now. The LED Flasher unit you need will cost between $30-60 dependent on where you buy it. Still worth it in my opinion

  4. Hi Sir,

    1. I am from India..May I know the impact on battery and power consumption if we use LED lights in Car of 1.2ltr diesel engine instead of halogen lamps.

    2. Also can you explain the visibility and clearance of road ?

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