power 4dIn collaboration with HAPPY POWER. Only 300PCS Produced. Features: Full Size 36x18; Our Champion-Grade Speed + Control Surface; Soft Rubber AntiGiven, Power of convex lens=4D. Placed at 40 cm from a wall. To Find, Distance of a candle. Solution, It is given that ,Power = 4D. Then, P = 1f. So, 4 D = 1f