I have not done this modification. But when I'm at Jorge's and Jemson's place [ Jemson's Auto Electrical and Jorge's Radiator Shop | Facebook ] I saw them (usually Roy) doing it on a lot of customers' cars. It makes the gauges look better and possibly easier to see while driving. Feels like a poor man's optitron or fine vision gauge.
Photo of the bulb used [they have shorter ones depending on the size of the bulb cavity]:
Suzuki Jimny gauge cluster being fitted (and the lens being cleaned but usually there is no need to remove the lens):
Jemson thread at Tsikot.com (for the other works they do): http://tsikot.com/forums/car-securit...mber%5D-64981/
You can buy your own bulbs or have the shop source them for you for a nominal mark up.