What is Cost Per Light?
Cost Per Light calculates the annual electricity cost to operate a single light bulb. This metric helps you compare different bulb types, estimate lighting expenses, and identify opportunities to reduce energy consumption in your home or business.
How to Calculate Cost Per Light
The formula accounts for wattage, daily usage, and your electricity rate:
[\text{Annual Cost} = \frac{\text{Watts}}{1{,}000} \times \text{Hours/Day} \times 365 \times \text{Rate}]
Where Rate is the electricity cost in $/kWh.
Where:
- Watts is the power consumption of the bulb
- Hours/Day is the average number of hours the light runs each day
- Rate is your electricity cost per kilowatt-hour
Calculation Example
Suppose you run a 60W incandescent bulb for 8 hours per day at a rate of $0.30/kWh:
Step 1: Convert watts to kilowatts:
[\frac{60}{1{,}000} = 0.06 \text{ kW}]
Step 2: Calculate daily energy consumption:
[0.06 \times 8 = 0.48 \text{ kWh/day}]
Step 3: Calculate annual energy consumption:
[0.48 \times 365 = 175.2 \text{ kWh/year}]
Step 4: Multiply by electricity rate:
[175.2 \times 0.30 = 52.56]
The annual cost per light is $52.56.
Another Example
A 10W LED bulb running 6 hours per day at $0.13/kWh:
[\text{Annual Cost} = \frac{10}{1{,}000} \times 6 \times 365 \times 0.13 = 2.85]
The annual cost per light is $2.85.
Comparison Table
| Bulb Type | Watts | Hours/Day | Rate ($/kWh) | Annual Cost |
|---|---|---|---|---|
| Incandescent | 60 | 8 | $0.30 | $52.56 |
| CFL | 14 | 8 | $0.30 | $12.26 |
| LED | 10 | 8 | $0.30 | $8.76 |
| LED | 10 | 6 | $0.13 | $2.85 |
Switching from a 60W incandescent to a 10W LED bulb at the same usage saves over $43 per year per light. Across an entire household with dozens of fixtures, the savings add up quickly. Use this calculator to evaluate the true operating cost of your lighting and make informed decisions about upgrading to more efficient bulb technologies.