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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.

2 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.

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