2021 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.

LED Turn Signal, Brake & Tail Bulbs

LEDs are much brighter and better these days than they used to be. Over the years I've continued to experiment and upgrade. In 2021 I'm finally happy with good LEDs I've found for all three types of lights.

Bulb Bases:

The turn, brake and tail lights all have a standard BA15S base. (a.k.a. P21W)

Factory Bulbs:

The brake light and turn signals use standard monofilament incandescent 21 watt 1156 bulbs.

The tail light has the same base as the 1156 bulb but is shorter and has a smaller diameter bulb. It is 10 watts and not as bright as the brake light's 21 watt 1156. A standard 1156 bulb will not fit in the K bike's tail light lens. Here's some examples of these 10 watt filament bulbs:


LED Color:

It is best to get LEDs that match the lens color: amber for the turn signals and red for the brake and tail lights. If you use white LEDs behind colored lenses then the color will wash out. For example, a white LED bulb will appear pinkish behind a red lens. Here's an example:

The reason for this is that a white LED emits a different spectrum of light than an incandescent filament bulb. As you can see in the graphs below, white LEDs don't emit much light in the orange and red wavelengths compared to a filament bulb.

Turn Signals:

These are the best and brightest amber 1156 LEDs bulbs I've found. They have 144 3014 SMD LEDs - 18 at the tip and 21 rows of six around the sides. They are bright and very visible, even in bright sunlight. Here's how they compare to a filament bulb:

IMPORTANT: Running LED turn signal bulbs with the factory flasher will cause it to malfunction. In order to run LED turn signal bulbs you either need a Kisan Signal Minder Model SM-6 (made specifically for K bikes) or you can do this simple modification to the flasher relay.

These can be found on Ali Express for about $3 each or you can buy four of them at Amazon for about $16.

Brake Light:


It's tempting to use 144x3014 LED like the turn signals in the brake light. However those generate a lot of heat if the bulb is on for an extended period of time, like when you're in stop and go traffic. This can warp/melt the tail light lens. For that reason I use a red LED bulb with 57 3014 LEDs that's still pretty bright for the brake light but doesn't generate a lot of heat. These have 12 LEDs on the top and 15 rows of three LEDs around the sides. I found this at Ali Express.  Be sure to get the BA15S in red.

Brake Light Flasher:

A good unit for making the brake light flash and then go solid is the GS-100A.

They can be found on Ebay here.

Tail Light:

Since the tail light is always on (at least for US K bikes) I wanted an LED bulb that did not generate much heat.  I tried five different LED bulbs and decided that this one with 12 3030 LEDs works best with respect to the tradeoff between brightness and low heat. Since the tail light compartment is not reflective like the brake light compartment is, LEDs on the side of the bulb do not make much difference. I purchase these from Ali Express. Be sure to get the red 1156 BA15S P21W.

NOTE: The outer diameter of this LED bulb is 20mm, the same as the inner ring of the tail light receptacle. Since the bulb needs to be angled when installed it won't fit unless you enlarge the inner ring a few mm with a knife, file, Dremel or other tool.

Bulb Monitor Unit (BMU):

In order to run brake and/or tail LED bulbs in you will need to disable the BMU. Instructions for that can be found here. (This is not necessary for turn signal LEDs, just the brake/tail.)

License Plate Light:

The tail light on K bikes serves two purposes. It's a tail light but the clear lens below is there so that it also illuminates the license plate with white light. (A legal requirement where I live.)

To light the license plate light I attached a white 14cm COB LED strip to the underside of the tail light lens.

These can be found on Ebay using this link.

Other K Bike LEDs:

Instrument Cluster LEDs:


LED Headlight Bulb:



A note on claimed lumen outputs for LEDs: Vendor claims of lumen output should not be used to evaluate how bright an LED bulb will be in real life. Here's the short version of why not:

* There is no standardized way to measure effective lumens.

* Effective lumen output can vary greatly depending up the reflector and lens used.

* Vendors lie. Many times the lumen figure they quote is the theoretical maximum of the LEDs used, not the effective lumens that the LEDs actually emit.


2021 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.