What is the efficiency of a CFL?

The correct answer is: More than 15%

• energy input = useful energy output + waste energy
• Efficiency (%) = (useful energy output ÷ energy input) × 100
• The luminous efficacy of a typical CFL is 50–70 lumens per watt (lm/W) and that of a typical incandescent lamp is 10–17 lm/W. Compared to a theoretical 100%-efficient lamp (680 lm/W), CFL lamps have lighting efficiency ranges of 7–10%, versus 1.5–2.5% for incandescents.
• So Its Less than 10%