The Tridonic PC 2x21/28-5 T5 Combo is a combination electronic ballast and emergency lighting unit to run: 2 x 21 Watt T5 fluorescent tube 2 x 28 Watt T5 fluorescent tube PC T5 Combo Ballasts have the following features: - Low profile casing - Lightweight one-part emergency lighting unit - Simple wiring - No compatibility problems - 1 or 3 hour rated duration - Hot lamp restart in normal operation - Cathode heating in emergency mode - AC operation of all lamps - Automatic restart after relamping in normal operation - Green charge status display LED - Optional test switch - Checking the emergency lighting function by interrupting the unswitched phase - Short circuit proof battery connection - Polarity reversal protection for battery. This should be used with a 5 cell battery pack