Hi, just a quick question. I've got a couple of US Philips tubes, one 2ft 20W and one 4ft 40W and they have 'TL-RS' on them, I'm assuming that RS refers to Rapid Start?

Are the cathodes in these any different to standard tubes? I've noticed they don't seem to glow as brightly at the cathodes during preheating as my others tubes and if you use a regular glow starter it takes a bit longer to start. I'm using electronic starters that preheat for about 2.5 seconds so could there be any problems using rapid start tubes on a switchstart circuit?

The difference to "normal" tubes is the controlled parameter of filament rating:
Preheat tubes are controlled to have tight tolerance characeristics when heated from a current source, so each tube model/maker (of the same tube designation) may have slightly different filament voltage, but all would have the correct temperature on the same current (same as the rated operating current for 2..3secod preheat time).
RS have controlled characteristics when heated from a voltage source, so all different models/make would have same filament voltage (3.5V), but may differ in current.
Usually the RS filament is designed for a bit higher current and preheaters for higher voltage, so "mislamping" lead to a bit lower temperature in both directions (as overheat would be more damaging, because the temperature is governed by the Power=Const*T^4 balance formula).
So the only problem would be with insufficient preheat temperature, but as electronic starters preheat electrodes for way longer then glowbottle, in reality it should be not big problem. Glowbottles would suffer higher wear with RS tubes, as it take them longer to strike the lamp (it take them longer to reach the minimum temperature required to ignite)...

My mother had in the past, a US GE FC32T9 Rapid-Start operated on a switchstart magnetic ballast with a glow starter, in the circular fluorescent fixture on the kitchen.
The lamp didn't lasted long. As soon as the starter became welded, the lamp went dead, because it refused to operate with the new starter.
So the lamp replaced to an Osram L 32 W/56 C made in Italy.

I guess the starter welded close, because the lamp refused to start and caused the starter to flash for long time... This is exactly the reason, why keeping "still working" starter inside the fixture after the lamp died: Mostly is very severely worn off, so it will likely cause excessive wear of the new lamp.
In reverse situation it is even worse: Lamp just close to EOL become marginal with starters, so if it flashes on one starter, it start with another. So replacing the starter may appear as solve the problem, but in fact after very short time the lamp wear a bit further and start flashing even on the new starter and then destroy the new one as well.

My mother had in the past, a US GE FC32T9 Rapid-Start operated on a switchstart magnetic ballast with a glow starter, in the circular fluorescent fixture on the kitchen.
The lamp didn't lasted long. As soon as the starter became welded, the lamp went dead, because it refused to operate with the new starter.
So the lamp replaced to an Osram L 32 W/56 C made in Italy.

@Medved: No. The lamp wasn't flashed. The starter was failed when the lamp was good, as the lamp suddenly refused to ignite, while the electrodes were red hot, without flashing.
After the electrician put the new starter, the lamp refused to be operate at all and the ends were black.
So i think the welded starter killed the lamp instantly, because it was a Rapid-Start lamp.

I dont know know if the frequency/voltage difference causes this or not, but I have had no problems with running rapid start lamps on preheat gear.  Most USA lamps say "preheat rapid start", but there are some that are marked specifically rapid start, such as the F30T12s.

The pre-heat/switch start and rapid start are sold as different lamps in Japanese market.

The line voltage is 100v, however the longer tubes use auto-transformer type ballast with switch start or rapid start.　　The difference is in inner or outer coating. 

The switch start type doesn't have any coating.