A starter, together with the ballast, ensures that the fluorescent lamp lights up. You only need to use a starter if you have a conventional ballast. When do u use a Philips S2 starter? Suitable for 1 tube from 4 up to 22W Suitable for 1 tube of 4-6-8-15-22W Suitable for 2 tubes from 4 up to 22W The S2 starter is suitable for a fixture that is using two lights but only one ballast. For more information about starters, please have a look here: Which starter do I need for my TL tube?