Low / High Beam LED

Thread Starter


Joined May 26, 2020

I have a LED light I would like to use on a motorbike project i am working on.

I would like help with working out how to create high and low beam.

So far I have worked out that 10V 0.5A is ok for low beam and 12V 1.6A is ok for high beam.

I need a device to drop the current.

I have attached a very basic circuit.

Please be patient because I really don't have a clue.




Joined May 26, 2020
to start with
i would suggest using a SPDT relay, terminal 87a/87 would have a potentiometer so you can adjust the brightness of the LEDs
( no one wants to be blinded :) )
terminal 30 will be the const from the switch that tells the lights to turn on and off
terminal 86 will charge the coil changing the output from 87 to 87a.
terminal 85 will be ground

once you have the LED adjusted so they won't blind people, you can get a voltage regulator matching the results you get after the potentiometer.

MC78T12 12V 3A Voltage Regulator should do the trick

you don't want to have 1.6amps flowing through the highbeam indicator light (it will get very hot)
also please use fuses


Joined Sep 24, 2015
The fundamental difference between high beams and low isn't how bright they are, though there may be a brightness difference, it's the aim of the beam. On low beam there is typically a shield inside the lamp (incandescent) to block the light from striking the bottom of the beam reflector. High beam is a different filament that is not shaded. The difference is in the light pattern. Low beams cast the beam only out and down whereas high beam casts out as well as both up and down. Hence, more light on the roadway ahead.

The purpose of low beams is to prevent blinding oncoming motorists. I've seen people with standard reflector headlamp assemblies upgrade to HID (High Intensity Discharge) but not have the shield. The result is a blinding light coming from the approaching vehicle. The driver - oblivious to how their actions affect others - things how great HID is. The fact is they've been installed wrong, or are not designed for that type of headlamp assembly. Projector type headlamps have a built in shield. High beams are typically in a separate assembly. SOME projector headlamps have a movable shield. When on high beam the shield is simply moved away allowing the beam to spread out up and down.

This I don't know for a fact, but I suspect may be true, a dimmed headlamp will still shine in the eyes of oncoming traffic. Also, the reduced amount of light necessary to NOT blind oncoming traffic may be so low that the purpose of the headlamp is mostly defeated.

I don't think your approach is the correct approach. Still, what do I know?! Check with your local police department and ask them about headlights. They know the law and may either be able to advise you or direct you to a source of information regarding local laws. Also keep in mind that local laws vary from state to state. Headlights (all vehicular lights) need to be DOT approved. Anything else is a ticket-able offense.

Audioguru again

Joined Oct 21, 2019
For years, JEEP and other Chrysler cars use their huge high beams for daytime running lights and blind on coming drivers when daytime is cloudy. Lately, VW and Kia cars copy them. They might dim them a little but they are still blinding.
Other cars use dimmed turn signals or low beams for daytime running lights.


Joined Jan 15, 2015
I agree with Tony on this. My truck uses dual headlights (two per side) and while all four lamps are the same the outside two are aimed lower to flood the road surface for a short distance in front of me the inside two are aimed higher for longer distance in front of me. My bike uses two beams in one lamp and the low beam has a reflector which helps flood the immediate road surface a short distance in front of me. I also have two side spots. When I switch to high beam the side spots turn off as does my low beam and the higher intensity non reflected headlight comes on. Just as a footnote the bike originally had incandescent lamps and what a difference going to the Daymaker LED lamps has had.

In your case you would do much better getting a LED HI/Low beam combination designed for your bike.



Joined Oct 7, 2019
Your 12 volt source of power is not really 12V. It is more like 14.5 volts when running and 12V when the engine is off.
I think you should produce full light at 11V and some light at 10V.
You should plan on surviving 17V for a time and short spikes much higher.
Some time some one puts the battery in backwards. Your project needs to survive that. Not work , just not make smoke and fire.


Joined Sep 24, 2015
I got the mental image that the TS has a single headlight and wants to replace that with an LED headlight. If that's so there ARE some LED types that light up one side for low beam and light up both sides for high. There should be no need for modulating the power to the lamp itself.


Joined Sep 24, 2015
Learning about some new technologies regarding headlight bulbs. Here's a video that goes through and explains a whole lot more than I ever knew about these bulbs. Also note that at 4:30 timestamp they show four bulbs. The one on the extreme right has the shield I mentioned early on. Before this video I didn't know that dual beam headlights put the filament in different places. Not much of a difference, but the reflected light pattern changes.


Audioguru again

Joined Oct 21, 2019
A number of people drive their cars at night with only their daytime running lights on because their car design is out-of-date.
Other people drive their cars all the time with the high beams on because they are ignorant.
School buses drive in daytime with high beams on to blind everybody.