Updated 14 June 1999.

Using white LEDs


In the past whenever something had to be lighted, we have used yellow LEDs(Light Emitting Diodes),

as a substitute for white light. But now white LEDs are available. We can finally get rid of those

pesky yellows.

Unfortunately the new LEDs are not 100% white ! , they have a small blue shade, which is more

notably in pictures than in real life.

As a conclusion the white LEDs are far better than the yellow ones.


I have taken some pictures of these white LEDs in use, and I have to apologize for the sometimes bad quality.

Here it is - the new white LED : 
  Another picture of the white LED

 Technical data :
 Typical Voltage  3,6 volt

 Calculation of resistors :

(Supplyvoltage - LED-voltage)/LED-current = Resistor

Example : Supply-Voltage = 20 Volt ,LED-Voltage = 3Volt

LED-Current = 20mA => (20V - 3V)/0,02A = 850 Ohm.

Use 0,5-1 Watt resistors (the above uses 0.34 Watt)

 Max. Voltage  4 volt at 20 mA.
 Max. Current  25 mA.
 Light Strength max. 2000 mcd - Typical 400 mcd
View Angle  60 Degrees
 Life Span  60.000 - 100.000 Hours (7-11 Years)
 Typical cost :  5-7$ (will of course get cheaper in time)


So what can these new white LEDs be used for. Well they are very bright and can be used

for lamps, spotlights and other things.

 An example of the brightness of the LED :

Here you can see the blueish light, but as

I stated before its much more notably

in pictures than in real life.




Here is what I have used the LEDs for.

The Spanish model railway manufacturer ELECTROTREN uses yellow LEDs as headlights for their

DSB MZ, and some of their other locs.

The yellow LEDs are on a small PCB, which are easy to remove. On the PCB there is 3 yellow

LEDs and 4 diodes. Pictures of the PCB can be seen here : Top-side - Bottom-side.

The schematic is as follows :

You now remove the 3 LEDs and the 3 normal diodes (the ones who are in series). I actually only

removed the outer 2 as the remainder is then left unconnected.

Now you place a zener diode instead of the normal diodes, and the white LEDs instead of the

yellow LEDs. It should be connected as this schematic describes :

The finished result :

The value of zener diode and the resistor, can be changed, but I found a value of 470 Ohm/5W for the

resistor and 3,3 Volt for the zener to be OK. You can also put 4 or 5 normal diodes in series instead

of the standard 3 - but it may be hard to fit them.

I found it to be VERY important where you connect the resistor - (I actually blew the output transistors

of my Delta-Decoder).

The resistor should be connected to the "PCB-connector" on right side of the driving direction.

The resistors and their connection can be seen here.

Here are some pictures to show the result. Again, be aware of the sometimes bad picture-quality,

and the fact that the light from the white LEDs looks more blue than they really are.

 The traditional before/after pictures



 View from the front with yellow LEDs

View from the front with white LEDs

View from the side with yellow LEDs

View from the side with white LEDs

More pictures of the finished result

Side view

Front/side view

Comparison between the white LEDs and the regular light bulbs

Side view

Front view

Please note the top white led.

It is much more white than the others. This LED was the first I bought, - the others was bought one week later, and clearly they are another type which are much more blue. So if can look before you buy, you end up with a better result.

 Comparison between the white LEDs and the Märklin 37350 (E-152) with small yellow LEDs

Side view

Front view

Front view, where the 37350 has both set of lights on

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If you have a question about anything I have written, then send me a mail

Email :kenneth@pallund.dk