In terms of the two cords. Many cold lights have a heater circuit powered by one cord and the lamp itself is powered by the other cord. What happens is that when the light powers on it is dim and it gets brighter as it warms up. The heater circuit keeps the lamp warm, that means that when the lamp powers on it stays at the same intensity throughout the exposure.
There is still some fluctuation of intensity on power-up, but usually it is good enough of a system for most B&W printing.