Understanding the Cost of Keeping a 120 Volt 100 Watt Light On 24/7

Have you ever wondered how much it would cost to leave a 120-volt 100-watt light on continuously?

Calculating Daily EnergyConsumption

Let's start by understanding the daily energy consumption of a 100-watt light bulb left on for 24 hours each day. The calculation is straightforward:

Power in watts 100 watts

Time in hours 24 hours

Daily energy consumption in watt-hours (Wh) Power × Time

Therefore, 100 watts × 24 hours 2400 watt-hours per day or 2.4 kilowatt-hours (kWh) per day.

Calculating Monthly EnergyConsumption

To find the monthly energy consumption, we need to multiply the daily consumption by the number of days in a month. Assuming a month has around 30 days:

Monthly energy consumption Daily energy consumption × Number of days in a month (approx. 30 days)

So, 2.4 kWh/day × 30 days 72 kWh per month.

Once we have the monthly consumption, we can calculate the cost based on the local electricity rate.

Calculating the Cost

In the United States, the average cost of electricity is around $0.13 per kWh. However, this can vary significantly depending on your location. For our example:

Total monthly cost Monthly energy consumption × Cost per kWh

$0.13/kWh × 72 kWh $9.36 per month.

For a more accurate estimate, you should adjust the cost per kWh based on your local electricity provider's rates.

Alternative Cost Estimation

Here’s a quick way to estimate the cost:

A standard 100-watt incandescent light bulb uses 100 watt-hours per hour.

Over a 24-hour period, it uses 2400 watt-hours or 2.4 kWh.

The annual consumption would be 2.4 kWh/day × 365 days 876 kWh.

Assuming an electricity cost of $0.15 per kWh, the total cost would be 876 kWh × $0.15/kWh $131.40 per year.

Comparing Incandescent and LED Light Bulbs

The cost can vary significantly based on the type of light bulb you use. A simple incandescent bulb uses about the same amount of power, but modern LED bulbs use much less energy. For example:

If the wattage is X (let’s assume 10 watts for a LED),

Days per month let’s assume 30.4 days/mo

10 watts 1 kW/1000 W, 24 h/day, 30.4 days/month

Energy consumption 10 watts × 1 kW/1000 W × 24 h/day × 30.4 days/month 7.3 kWh.

Cost 7.3 kWh × 0.30/kWh $2.20 per month

Conclusion

As you can see, the cost of keeping a 120-volt 100-watt light on for 24 hours a day is not as high as you might think. It is crucial to consider the type of light bulb you are using, as this can significantly impact your monthly electricity bill.

Remember, energy prices and lighting technologies can vary greatly, so always check the specific rates and wattage of your light bulbs for the most accurate cost estimation.