The 'T' designation on a contact normally means 'tungsten'. In this case the maximum incandescent wattage is 360Watts [120v x 3A]. Lightbulbs have a very high current when they are turned on and can weld the contacts shut if the contact current is not derated.
Originally Posted by Donald Qualls
A cold light head's inductance causes a problem when the circuit is opened/turned off. The current in the head wants to keep going - think flywheel - and as the contacts open the current forms an arc accross the contacts causing pitting. A capacitor/resistor [called a snubber] accross the contacts will quench the arc. If you remember old car ignition systems there was a capacitor accross the distributor points and this was required because of the inductance of the ignition coil.
If you are worried about the timer/head combination I would contact the manufacturer of the head.