Smaller tubes exhibit higher thermal resistance tube -> ambient air.
So to dissipate the "waste" power, larger temperature difference to ambient is necessary.
So first thing: smaller tubing run on higher temperature.
Second thing: All fluorescent tubes are optimized for given operating temperature, so they do not light properly, when they are colder or hotter.
These two things mean, then smaller tube are designed for higher (cold spot) operating temperature (by amalgam mix composition).
So after power ON you should wait, till they reach such temperature.
And as thermal resistance is larger, so the time-constant of the Resistance (~1/air flow) x Capacitance (~mass)
So you get system with longer time constant, so longer time necessary for temperature settling.
There are few ways to overcome the issue:
1 ) Use large surface, low intensity tube, so the operating temperature nearly equals the ambient, so no thermal settling necessary. The oldest method (used on T12), partially used till T8.
2 ) As the pressure is the main parameter and it is controlled by the temperature of "cold spot" (not the lowest temperature point, but the point dictating lowest mercury partial pressure - on amalgam lamps not the same point) only, so the "cold spot" is in small tube end protruding away from lamp's heat (T5 behind electrode on the end with the etch, in Megaman CFL's prolonged evacuation tube). But in CFL's, even this point is way hotter then ambient, so still you have to wait, till the temperature rise here.
3 ) Boost the input power to compensate for the low temperature efficacy loss. Very efficient method, best when combine with some previous. You get the light immediately and at the same the boosted power heat up the lamp quicker, but need technically dimmable ballast, controlled by lamp temperature sensor (the best, might compensate for wide ambient temperature variation) or lamp temperature simulator (simple - settling of an RC emulate temperature settling. Might loose synchronisation - after hot restart the lamp is hot, but RC discharged...)
I noticed on the smaller tubing/lower wattage Megaman CFL's the starting and warm up time is longer than the larger tubing/higher wattage ones. What causes this, PTC size?
