http://en.wikipedia.org/wiki/Glow_plug
Not all "glowplugs" are the same. In my Perkins 4.108, the cold start device consists of a small heating element that plugs into the air intake manifold. Diesel dribbles onto the red-hot coil and ignites, and is then drawn into the combustion chamber. This device stopped functioning one time when it was cold, so I got a can of WD40 and a cigarette lighter and made a torch, directing the flame into the breather while the engine was turned over. Worked fine.
My cold-start device takes about 4 seconds to do its job.