Bruce has it correct. Think of it this way: If an incandescent Whelen or Grimes lamp (which puts out an IMPURE "white"....really a "warm-white" beam) is placed behind an aviation green or aviation red lens.... then the resultant glow is the product of that lens "filtering out" all the visible spectrum EXCEPT aviation red or green. So a large amount of the visible light spectrum which the incandescent lamp produces is.... BLOCKED by the colored lens. And that is a reduction of the output capability of that incandescent lamp.
But if a RED or GREEN lamp is substituted, then MORE of the desired spectrum is produced to begin-with....and LESS unwanted spectrum is blocked and therefore lost. The result is that for similar initial-outputs.... the colored lamps will eventually pass more of their light thru the aviation lens.
This was demonstrated when I first installed a "white" LED behind the colored lenses .and the visible result was not red or green... but was amber and blue. It turns out that very little of the light produced by that "white" LED was in the aviation red/green spectrums ...and therefore very little light passed thru the lens....and further what little light passed was not the desired spectrum (color) because so little of that spectrum was actually available to be filtered.
Additonally, I discovered the 5mm "super LED's" from the website were indeed much brighter in whatever color desired. Although those are slightly larger devices, and when fitted to the fixture they actually make contact with the colored lens.... I think that's a better lamp to use, and the physical contact between the LED and the lens is unimportant because vibration is not an issue with LEDs as it is with filament-type lamps which have glass globes.
Another point: The Whelen or Grimes wingtip navigation lamps can puzzle one who has never worked on them. The fixtures are not like automotive fixtures in that they are "bottomless". If one attempts to install/remove a lamp one might find it frustratingly difficult due to the "tightness" of the "fit" of the lamp within the socket. This is due to the threaded "ferrule" which holds the actual spring-loaded contact in the bottom of the fixture.
The Answer? Remove the entire fixture from the wing (this involves two simple phillips screws which mount it to the wingtip) and "unscrew" the ferrule a few turns. Or all the way, if you like. The lamp will now be easily removed.
Install the new lamp, then re-attach or screw the ferrule back onto the base of the fixture until "snug". (Don't force it too tight. The ferrule will accomodate lamps of various minor imperfections in this fashion.) Now reinstall the assembly back onto the wingtip. Reinstall te lens and lens cover/retainer, and enjoy!
You will likely only have to do this ONCE in your lifetime, as LEDs will outlast incandescent lamps by decades. (Use a dab of silicone grease or Dow Corning DC-4 smeared onto the base of the lamps. This will prevent corrosion over the long-term, and is a good idea for ALL types of lamps.)
As a concluding comment, I found the best LED for the WINGTIPS to be their 36 Super Bright S25 LED Light, Product Code: 49785 , Price: $13.99 ... RED and GREEN.
http://www.ledlight.com/s25-36-super-br ... light.aspx
For the TAIL, I found S25 39 LED Light , Product Code: 48451, Price: $14.99 in WHITE to be best.
http://www.ledlight.com/s25-39-led-light.aspx
In all cases, it is the 1156-base which worked for me, and I used a bench-grinder (but a file would also be fine) to grind off ONE of the pins on the base of the red and green lamps. This allowed it to fit the staggered-pin socket of the wingtip lamp sockets. The tail light does not need alteration. Nor does any interior lighting require alteration, as LEDs are made with the common bases already in use. (All the original aircraft interior lighting is common automotive lighting.)
Summary & Disclaimer: This is not an "approved" replacement lamp by authorities, despite the fact that Cessna has abandoned FAA-PMA lamps for taillight fixtures and now lists a common automotive lamp for the tail nav light, and despite the fact the LEDs will meet/exceed light output while drawing incredibly lesser amounts of current and produce nowhere near the heat of incandescent lamps. Whelen now produces approved LED navigation lamps for aircraft should this experiment convince you as well as it did myself, to convert to LEDs.
<EDIT> However Advisory Circular 23-27 provides the basis of approval for using automotive lamps in aircraft built before Jan '71. I have been using these in my airplane now for 2 yrs and am very satisfied with them. One should make a log entry to the effect that LED "standard part" lamps have been installed as direct replacements. IMO
I resemble that!!!! 
The problem with trying to demonstrate LEDs in northern Minnesota is that it does not get dark until well after sane airmen are in bed (asleep 
). 