A 4.0 W LED bulb produces 240 lumens. What is the efficacy of the bulb?

1. 1.7 lm/W

2. 60 lm/W

3. 236 lm/W

4. 244 lm/W

Efficacy is the ratio of light output from a lamp or a bulb to the electric power it consumes and is measured in lumens per watt (LPW).

In this case; the power is 4 watt and the number of lumens is 240.

Efficacy = lumens/power

= 240/4

= 60 lm/W

Thus the efficacy of the bulb is 60 lm/W