How much electricity does a 100 W light bulb consume?

You can easily calculate the real consumption of electrical appliances or light bulbs by using a wattmeter, which can be purchased in centers for around one hundred kunas. Sometimes consumers have deviations and consume a little less or a little more than the declared power. You can also measure consumption by turning off all consumers and turning on only the consumer whose consumption you want to calculate for an hour, and write down the state of the meter before and after the measurement. Take into account that devices in stand-by mode (turned off television, refrigerator, wifi router) also consume some energy, but this method will give you an accurate consumption result.

What is a kilowatt-hour (kWh)?
When used in conjunction with the unit of time, the term watt is used to express energy consumption. For example, a kilowatt-hour is the amount of energy consumed by a device of one kilowatt in one hour.

If a 1 kW device works for exactly one hour, it will consume 1 kilowatt-hour of energy.

1 kW * 1 h = 1 kWh

 
What is the price per kilowatt-hour?
In Croatia, according to the current price list of HEP ODS, you will pay HRK 0.95 (VAT 13% included) for 1 kilowatt-hour of energy with two-tariff household tariffs during the higher daily tariff. During the lower daytime (nighttime) tariff, one kilowatt-hour of energy will cost you HRK 0.46 (VAT 13% included).

How much electricity does a 100 W light bulb consume and how much does it cost?
If we turn on a 100 W light bulb and leave it on for an hour, it will consume HRK 0.095, i.e. slightly less than 10 Lipa.

0.1 kW * 1 h = 0.1 kWh * HRK 0.95 = HRK 0.095
If we turn on the light bulb during the day and leave it on for 10 hours, it will consume HRK 0.95.

0.1 kW * 10 h = 1 kWh * HRK 0.95 = HRK 0.95
Roughly speaking, the answer is: a 100 W light bulb will consume HRK 1 after 10 hours. If it is turned on for 10 hours every day during the month, the cost will be around HRK 30.

With two-tariff meters (white tariff model), the bulb would also consume 1 kWh of electricity during the lower daytime tariff (night), but you would pay half as much - HRK 0.46.

Amount at the end of the month
Although apparently it is a small consumption, let's show with an example how much smaller consumers can spend on a monthly basis. Let's take for example an LCD TV with a declared power of 150 W. So, the power of this TV is slightly higher than a light bulb. If the TV keeps you company every day while you work, you might be surprised at how much it actually costs. Let's assume that you have the LCD TV on for 10 hours every day.

Daily consumption - 0.15 kW * 10 h = 1.5 kWh = HRK 1.42 Monthly consumption - 1.5 kWh * 30 days = 45 kWh = HRK 42.75
From the example above, it can be concluded that 10 hours of LCD TV operation every day at the end of the month costs HRK 42.75.

You can check the informative calculation of the price of consumed electricity with the HEP ODS calculator.