Step 1 find the number of INC bulbs needed over this bulb's lifetime

50000 / 750 = 66.6667

Step 2 determine the cost of replacement INC bulbs and the difference with this bulb's cost

66.6667 * $0.50 = $33.33 cost of replacing the INC bulb

$33.33 - $44.95 = ($11.62) replacement savings

Step 3 determine energy usage over the life of this bulb

90 watts * 50000 hours / 1000 watts per kW = 4500 kWh

17 watts * 50000 hours / 1000 watts per kW = 850 kWh

Step 4 subtract to find the difference in energy usage between the bulbs

4500 kWh - 850 kWh = 3650 kWh lifetime savings

Step 5 find the lifetime energy cost savings

3650 kWh * $0.118 = $430.70

Step 6 combine energy savings with replacement cost savings to find total lifetime savings

$430.70 + ($11.62) = $419.08 total lifetime savings

Step 7 find savings per year

5 hours per day * 365 days per year = 1825 hours per year

1825 hours per year / 50000 lifetime hours = 3.65 % of bulb life used per year

3.65 % * 3650 kWh lifetime savings = 133.225 kWh yearly savings

3.65 % * $419.08 lifetime savings = $15.30 yearly savings