I use the Seitz mike/lip lights on almost all night flights, and prefer the green LED/white xenon model. The xenon's too bright for almost all night duty applications however, so I also carry a PAL light (
http://www.palights.com/) for starts, paperwork, map data, etc.
In the stone age, pre-mike light days, I'd use a red filter on a AA Minimag with a ball cap clip, or just stick in under the headset arch, above the ear cup, when the flight continued into the dark.
The mike/lip lights are priceless. Most VFR aircraft interior lights are widely variable quantities and quality throughout the fleet. Add to that the fact that night flights might be in well illuminated conditions or black, black, black!, and having a handy, reliable light to read the gauges becomes a real asset. That's how I use it- interior's as dim as possible and quick illum to see the gauge of interest.
As to pistons at night- Recips ain't what they used to be, hallelujah! I can't cite a source, but my inderstanding is that the plant in the R44 compares favorably with the C20s common older helos.