What Continuous Brightness
Brightness Lighting tries to overcome the
prevalent problem of lighting in model
locomotives. The problem is that when the train
starts to move the locomotive (headlight) is
completely unlit, and as the train speeds up (i.e.
higher voltages applied) the light gets brighter.
The worst part is, even at top speed the light is
usually nothing more than a dull orange glow from
are various solutions to the problem, but so far
none of them have been satisfactory from the
modellers perspective. Previous solutions are
almost always unsuitable for smaller scale
modellers as well, simply because of the size of
have always felt the use of LEDs has been a great
option. Not only do they run cool, but they never
need replacing. Being plastic, they can also be
highly shaped to fit the particular application.
Many have felt the same but the problem is how to
drive them? LEDs require a certain voltage to
make them start working, and past this will
consume all available current. Typically a
resistor would be used to resist the current
flowing through them. This stops the LED from
burning out, but leads to the same problem we had
from the lamps. The LED only lights dimly at low
voltages, and gets progressively brighter as the
train is sped up. We should also put a diode
inline with the LED, so that reversing the
locomotive, and the back EMF generated by the
motor, does not damage the LED. Now our LED will
not even start to light until we are moving along
at some speed.
voltage regulators have some acceptance in the
railroad modelling community, they are a very
poor solution to the problem. Most have dismal
performance, and are difficult for modellers to
employ. I have posted some information here, if you
are interested in reading the drawbacks of this
Solution, the LM334Z
solution I have found is a small chip from (nominally)
National Semiconductors, the LM334Z. This comes
in a very small package (TO-92), smaller than the
LED. The LM334Z is a "programmable current
source", what this means is that the chip
will allow only a certain current through it,
irrespective of the voltage. "Programmable"
only means that you can set the amount of current
yourself. This is done with a single resistor.
The unit can take forward voltages up to 40V, and
needs no protection against reverse voltages (i.e.
the locomotive is running in "reverse")
for voltages up to 20V. Both of these exceed the
nominal 12V of model railroads by a very
The unit will
only light in "forward", giving directional lighting
without any additional diodes (which cause voltage loss).