Sensitive gate general purpose triac from ST suitable for use as an on / off function in applications such as static relays, heating regulation, induction motor starting circuits, light dimmers and motor speed controllers.
....it's part of a rather nice lamp in our lounge.
The lamp in question uses old skool incandescent bulbs of the halogen variety. The 300 watt R7 tube bulb had blown the triac and tripped the light circuit and also blown a little 20mm 2.5 amp fuse inside the lamp.
I looked for a replacement dimmer circuit but this one was obviously built just for this lamp. Fortunately I was able to find a similar but up rated version of the triac at Rapid.
Soldering it in was easy but obtaining normal lead/tin solder required a trip to China via ebay since Rapid refuse to sell it to humans, only to corporations.