HO scale

I use ready wired LEDs available from several places such as ledbaron on ebay.

Ngineering makes the outside light fixture in a kit.

I'm using SMD LEDs for outside lights - shown here by night and day:

For lights inside a structure I'm using standard LEDs.

They all are fed via a rectifier, since all my modules have 10 V AC as power source. The rectifier, resistors and switches for the LEDs are mounted on the bottom side of the modules.

For older structures I use warm white LEDs, for newer structures I use bright white LEDs.

You can buy SMD LEDs with feeder wires already soldered to them.

I should have specified SMD LEDs - I use a 12 volt wall wart with appropriate resistors.

I make styrene boxes that serve as "rooms", drill a small hole in the ceiling and epoxy the LED there.

A simple multiple LED resistance calculator is available here:

http://ledcalculator.net/default.aspx?values=5,3.6,30,15,0&sms_ss=favorites

Another good colour for older buildings, especially farm houses and the like, is "golden white" - gives that old-fashioned yellowish glow.

Cheers

Tony

Don't discount using Tamiya clear colours such as amber to change the bright white LED blue colour cast to a more suitable and subtle golden white.

This may be a cheaper option than buying golden white LEDs.

To change to perception of colour, apart from using different resistors to vary the intensity, consider multiple coats, or indeed mixing with other clear colours such as yellow, red or even red to change the hue.

Cheers

Simon

First you need to determine what you are going to use as a power source. You will need a minimum of 3 volts. But whatever the voltage you will also need a resistor to limit the current draw. For me, I use a 12 volt DC power supply and run a bus supply around the layout. Excellent suggestions on type and size of LED already. In terms of where to buy, have a look o Ebay. There are a number of suppliers based in Hong Kong who sell LEDs prewired with resistors at very low prices and often freight free world wide.
Peter

"Different resistors" is indeed important. The LEDs are normally way too bright when used with the minimum resistor required.

I often use 2000 to 5000 Ohm instead the required 500+ Ohm.

I have been collecting LED strip lights for my future buildings. Many of these types of lights are already set up for 12v power and you can cut them apart at each marked location. I just solder some leads to each section after cutting them apart. You normally get about 3 leds at each cut line.  Some of the newer strips are actually 24v so they can run longer strings before adding another power supply but I also have some 24v led power supplies to work with. I work as a trade show electrician and have been able to get mine for free as throw aways or surplus. Wall warts and led power supplies are getting pretty cheap. With my 12v leds, I could even use my current 12v dc power bus for my future RailPro control system but since I already have extra 12v supplies, I might just run another lighting bus.