These lights are often on the periphery. For a great deal of the time they aren't attracting much attention at all. During short segments of your flight. however, they are much attended to (gear down and locked - okay! ... Outer marker - Where's the rabbit?) And occasionally they really make your blood pressure shoot up (Hydraulic Pressure - LOW).
In a sim, annunciator lights are also on the periphery. They don't get much attention when you're building your simpit because they're way down on the list AND they can be expensive. Now there are some clever ways to use plastic overlays and tree lights that look quite nice, but for a little more effort and not much money, it's possible to make some authentic looking annunciator lights and gain another step up in "reality".
Home building supply stores like OSH and Home Depot carry an assortment of extruded aluminum shapes, which when combined with some epoxy, some plastic and a bit of simple electronics, can produce lights like these.
Both of these lights were made by using five minute epoxy to join off-the-rack aluminum shapes. ("Filled" epoxy, epoxy that comes pre-mixed with powered metal or silica, seems to be stronger than clear epoxy.) The legends were made with dry transfer rub-on lettering placed on a bit of Plexiglas that was frosted by wet sanding with 80 grit sandpaper. The legends could just as well be made by printing on a transparency and sandwiching that between the frosted Plexiglas diffuser and the clear front piece.
Here are a couple of exploded diagrams that show the general shapes that went into making these lights.
The circuitry is pretty basic. (This describes the large two-color annunciator. The smaller has only one LED chain.) Although one could use simply a resistor-LED combination, investing in a bit more provides some valuable benefits. Adding a driver transistor greatly reduces the current required from the control line. If you have an I/O board that provides standard logic levels out, you won't be able to directly drive much. The addition of the driver transistor gets around that limitation, plus it will let your I/O card run a bit cooler and hopefully last longer. Toss in a few diodes and you get a "lamp test" line as well. The 470 and 180 Ohm resistors are 1/2 watt units. The others can be as small as you can conveniently work with. The diodes are generic switching types, 1N4148 or what have you. There are only two red LEDs compared to four green ones because the greenies I had on hand just couldn't pump out the photons as well as the red ones. If you don't have these LED's on hand, I would suggest buying high output units with clear bodies as opposed to diffused. They cost only a few cents more and the difference in light output is amazing. If you change the number of LED's, you should change the load resistor value as well. Generally you will want about 20 milliamps through the LED's, so pick the load resistance as: (12 - 2.1 * number of LED's) / .020 . You can adjust the value a bit to obtain a good balance between red and green brightness. The transistors are shown as 2N7000's. You could just as well use VN2222's.
One last word; there are no dimensions on these drawings. This section is meant to be a suggestion of how to approach making realistic annunciator lights in general, rather than a specific plan for making one particular unit. Your specific dimensions will depend upon the particular aircraft you're modeling your simpit on, however, the length should be long enough to allow the LED's to evenly illuminate the frosted plastic diffuser.
Have fun.