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You were successful in persuading the management team at Superdamp (a clothing store selling expensive clothing imported from Japan) that they should consider replacing the display lighting at one of their large stores with LED lighting.

Now you have to provide data to show them how much they could save:


Each x represents a single 50W halogen light bulb.

4x and 3x represent spotlights with 4 or 3 bulbs. Each bulb is also a 50W halogen bulb.

Here is some data. The 5W LED and 50W Halogen are equally bright.

Light bulb Type


5W LED Spot 50W Halogen
Light bulb projected Lifespan (Hrs)


25,000 2,000
Cost per bulb


9.99 1.50

The lights in the shop are to be switched on for 14 hours per day (Mon - Sat) and 8 hours per day (Sun). Assume that the shop is open every day of the year (it is only closed on Christmas Day, New Year's Day and Easter Sunday). Assume that there are 52 full weeks in a year.

The company is ready to upgrade the store and is trying to decide whether to install new halogen bulbs or replace them with LED spots. Whichever they choose, they intend using them for 5 years before the next upgrade.

Electricity costs 15p per kWh. Assume that this price will stay the same over the 5 years.

Your task:

 You will be provided with the above data and some instructions on how to analyse it. You need to carry out the calculations to show whether LED lighting is cheaper than Halogen bulbs over 5 years.


1 kilowatt (kW) = 1000 Watts (W)

Units of electrical energy    =  Total power    x     Time

              (kWh)                            (kW)              (hours)


Cost of electricity     =     Number of units    x     cost per unit

                ()                        (kWh)                        (/kWh)