I'm often asked what bulb should be used for an an existing STT (Stop Tail and Turn) light which has an 1157 bulb in it. My answer is always, "there aren't any". In a rare situation a cluster bulb will work and give good light out-put, but that is the acceptation and not the rule. In those rare situations the end user put foil or foil tape to increase the light by reflecting off of the foil and the end result was an acceptable amount of light.
Primarily, the reason why
someone wants to use LEDs on the outside of any vehicle is safety. The
reason why they are safer is two fold. If the light is designed
correctly the result is more light and thus you are more visible on the
road. That is not to say that your lights should be so bright that you
are a hazard, by blinding your fellow travelers, but just enough for you
have good visibility when you are turning or stopping. The other reason
why LEDs are a good choice is it takes many of them to make up the
amount of light that is needed. If you have a failure you still have
lots of light. In an incandescent bulb you have one filament and if you
have a failure you have NO light.
One of the main
reasons why cluster bulbs don't work well is they product about 1/3 as
much light if the cluster bulb is about the same size as the
incandescent bulb your replacing. The other reason is most of the STT
fixtures are designed to refract and reflect light from one single
Below are two pictures which have a STT
light and some markings that illustrate what happens when you use a
cluster bulb in some STT lights.
On the next picture ( below) is what a cluster bulb looks like ( as crude as it is :-) in the same light fixture.
points of light being refracted and reflected has a result of the
light going in many different directions. In the event that your cluster
bulb was to produce more light (they seldom do) than the incandescent
bulb, it would not be as effective ( and safe) because the light does
not all show up at the intended target, the guy behind you.
As a rule of thumb, LED pads (which have all
the LEDs facing outward) give more light and are a much better choice.
If you notice, all the new cars have a pad style set-up that point in
the same direction and thus they give more light.
the present time we have discontented that first light kit and have
another sealed light insert that is much easier to install and gives
great light. LED-kit2
purpose of this blog post is not to promote the kit as much as it is to
steer folks in the right direction, of what to look for, when trying to
retrofit their older units with LED light.