Now these lamps are normally switched on at about 7 pm every evening and stay on up to about 11 pm when everyone has gone to sleep. That is, they are permanently on for about four hours every day or 120 hours per month.

To find out how much energy is saved, we multiply the power saving by the time in hours. That is, 175W x 120h = 21,000Wh. But electricity is sold in kilo-watt-hours (kWh) and one kWh = 1,000Wh. Therefore, I will save about 21kWh every month.

My most recent power bill shows that I consumed 284kWh for which I was charged Sh5,602. In other words, the average consolidated cost per unit (inclusive of all taxes and levies) was Sh19.72.

So, I expect to save about 21kWh x Sh19.72 = Sh414 each month. Is it worth it? Well, I paid Sh130 for each LED light; Sh650 in total. Therefore, they should pay back within a month and a half through saving.

The only question then is: will the LEDs last that long. Well, the box says that they have a 20,000h lifetime, so, ideally, they should live for the next 13 years. I will give you an update in the year 2030!; Twitter: @mungaikihanya

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