The luminous efficiency or efficacy of a light bulb is the r

The luminous efficiency (or efficacy) of a light bulb is the ratio of luminous flux to electric power input.

A)Determine the luminous efficiency in percentage form of a 100 W, 1700 lm incandescent bulb.

B) Determine power input for a compact fluorescent bulb to produce the same number of lumens if its luminous efficiency of the CFL bulb is 65 lm/W.

If the luminous efficiency of an LED bulb is 85 lm/W, determine the power input needed to produce the same number of lumens as the incandescent bulb.

C) Determine the cost of leaving each light bulb on for 5 hours a day for 30 days if the cost of electricity is $0.13816/kWhr

Solution

A)

Luminous efficiency :

n = 1700/100 = 17 lm/W

B)

For CFL:

n = 65 lm/W

So, Power, P = 1700/65 = 26.2 W <----answer

For LED:

P = 1700/85 = 20 W <------answer

C)

For CFL:

Energy used, E = P*t

= 26.2*5*30

= 3930 Wh

= 3.93 kWh

So, cost = 0.13816*3.93 = 0.543 $

Similarly For LED:

E = 20*5*30

= 3000 Wh

= 3 kWh

So, cost = 3*0.13816

= 0.414 $