Dark has mass. When dark goes into a dark sucker, friction from this mass passing through another mass will generate a certain amount of heat. It is commonly known that an operating dark sucker generates heat. The dark suckers with the greatest capacities force the dark to travel through the impeding mediums at greater rates of speed, so they develop greater amounts of heat. Thus, it is not wise to touch a operating dark sucker.
Candles present a special problem.
Though the light does not have to travel through a solid substance like the glass forming an electric bulb, the dark must travel into the solid wick, instead of a void as is found inside of the bulb. As we all know, this process generates a great amount of heat. In fact, flammable items which come into contact with an operating candle will be set on fire because of the amount of heat generated. Thus, it can be even more dangerous to touch a operating candle. Further proof of dark's mass is illustrated by the smoke generated by inefficient or extinguished candles.