LED's (Light Emitting Diodes) have been around for some time. They were originally produced in red, green, and yellow, and have been used in many applications. Recently we have seen them produced where they produce a light that is both white and bright. They are still pretty expensive (up to $7.00) as compared to a grain of wheat lamp, but draw much less current, and project a fairly focused beam. It also can be said that when they are run within their ratings, they are more reliable than lamps.
These white LED's are now being used for many headlight applications. They produce a beam that goes further down the track than most bulbs. In fact, a beam in a dark environment can be bright enough to show up at ten feet. The downside of these LED's is that the beam is concentrated in one direction, and very little light can be seen from a side angle. Some manufacturers use a frosted diffused LED which can been seen in all directions, but will not cast much of a beam in dim light or darkness. They light up the general area in front of the loco instead of casting a down the track. So you have a trade off as to weather you want a bright focused beam, or one that is readily viewable from more than one angle. The ideal size of LED's for most headlights headlights is 5 mm. Anything larger than this size is too large to mount on a loco.
The most common white LED is not really white. The actual light is bluish and is similar in color to a mercury vapor street lamp. This is a totally unacceptable color for a loco headlight, since they have a yellowish cast to them. As you may recall, the early steam locos had a fairly dim headlight, which was very yellow in color. Even the early diesels which had brighter headlights, still had a slight yellow tinge to their beams. The modern diesels have halogen lights, which are brighter than previous applications, but they still do not have a blue cast to the headlight beam.
The white LED can be modified to change the color without losing too much intensity. I have found that Tamiya X-24 Clear Yellow removes most of the blue cast. This is an acrylic paint which flows real well when painted onto the LED surface. Don't put too much paint on the LED. A thin film will block the blue color without degrading the strength of the beam. Paint the LED with either a dry brush or air brush for best results.
You cannot hook an LED directly to your previous headlight leads. A resistor needs to be inserted into the circuit to keep the current from becoming too high and blowing the LED. It has been found that a 700 ohm or 800 ohm resistor works well when connected to one of the leads of the LED when your track voltage reaches 22 volts. This value of course varies with the track voltage that you are using, and some experimentation may be necessary. If you are in doubt, it is best to buy one of the kits that has all the components in it. Walthers has kits with white LEDs that include the proper value resistor. RAM products (www.ramrcandramtrack.com) makes a ready to use white headlight LED circuit. Since it runs on 9 Volts, you will also have to order the RAM kit that drops track voltage down to the 9 Volts that this system requires. Sierra sound systems also have the ability to handle LED's rather than bulbs for their sound card headlight outputs. There are other sources of LED headlight products on the market. One only has to search the internet, or the advertising pages in Garden Railways to find similar products. JSE Electronics (www.jselectronic.com/golden.html) sells golden LEDs on their website. They accomplish the color change using an orange lens which is placed in front of the white LED. The downside is that you look at this orange lens when the power is shut off. Richmond Controls (www.richmondcontrols.com) is also another source of white LED's for model railroad applications. They also have a section on their website for the hookup and control of these devices which provides the calculation for components needed to successfully hook up white LED headlights.
Whatever your choice, you will see a remarkable difference when you replace your regular headlight bulbs with white LEDs, especially when you run trains at night. We have many club members that are very familiar with this conversion and will gladly help you if you decide to make the change. John Colbert is one name that comes to mind as a club member who is excellent with electronics. JColbert1@tampabay.rr.com