LED voltage

I bought a couple LED lights that I plan on installing on my son’s battery powered jeep (he’s sad that it doesn’t have head lights). The LED’s say to connect to a 12V battery. Given the location constraints I’d really rather just use a single 9V battery. Anything else is going to require some fairly major demolition of the jeep.

So my question is: Will it work? With a filament light it would just be dimmer. But I know the LED’s use an electronic control system. I would just connect it and see but I didn’t want to risk damaging the lights if I didn’t have to.


it depends; if they’re meant to connect directly to 12 volts and don’t have anything like controllable brightness then there’s a good chance the only “control” they have are current-limiting resistors. in which case, connecting them to 9V would only mean they’re dimmer, just like an incandescent.

OK. I’ll try them out with the 9V and see what happens.

I think the answer would depend on what the electronic control system does. If it accepts a wide range of input voltages and outputs a constant current then you should be fine. Even “12V” batteries vary in voltage according to the amount of charge and load. Does the label or datasheet state a range, or just 12V?

ETA nothing bad should happen if you test them at 9V; worst case is they will not light

I’ve tested several LED lights sold as vehicle accessories. Most of them don’t seem to have any regulation circuitry, just a resistor in series with the LED. They turn on around 9 or 10V, and when you apply more voltage, they draw more current and get slightly brighter. Some turn on at a lower voltage - it’s a function of how much voltage drop is across the resistor vs. LED. So you just have to test it.

Better lamps have current regulators. They suddenly turn on at a certain voltage (actual voltage depends on the model), and increasing the voltage above that point results in lower current (approx. constant wattage) and same brightness.

p.s. You could perhaps add a buck boost converter like this to boost the voltage from 9V to 12V.

Came to say the same thing as scr4, except this one is even cheaper, $5 for one or $2/ea for 5.

Note that you have to set the voltage correctly when you get them, before you connect them to the lights.

LEDs work very differently from incandescent bulbs with respect to power. An LED needs a voltage that corresponds approximately to the number of electron volts of the photons it emits, something like 2 or 3 for red and something like 4 or 5 for blue. When you give an LED less than that voltage, it basically does nothing. But if you keep increasing the voltage, once it reaches its threshold it then draws more power as a very steep function of voltage, so steep that you are likely to destroy it if you try to control the voltage. Much better to control the current. Lots of little LEDs can handle something like 10 to 50 mA. With a known voltage well in excess of the LED’s requirement, operating it in series with a resistor is very expedient and that’s a pretty typical use. In that case, the amount of light the LED puts out will be pretty nearly proportional to the power supply voltage minus the LED’s required voltage.