When the AC Power line fails, the transistors in this circuit are biased to conduce the current to the load. In this application the load is a small incandescent lamp, but you can use white LEDs. Suitable resistor must be wired in series with the LEDs according their currents. The values between brackets are for the 220 AC power line. Q2 must be mounted on a small heatsink. In some cases R2 must be altered to reach the best performance. The 6 V supply can be formed by common C or D cells.