Luminous efficacy is the measure of lamp efficiency. It indicates how much luminous flux a lamp generates from the power it consumes in lumens (lm) per watt. The higher the ratio of lumens to watts, the more efficiently a lamp converts the electricity supplied to light. Here are few examples:

• incandescent lamp 12 lm/W
• halogen lamp 20 lm/W
• energy-saving lamp 60 lm/W
• tubular fluorescent lamp 90 lm/w.
  
  

Coloured LEDs achieve 50 lm/W; white LEDs at present reach more than 30 lm/W – and higher luminous efficacy ratings are anticipated.