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Your desk lamp probably costs less than $2/year to run. But knowing the exact number — and how to reduce it — is straightforward and occasionally surprising.
The formula
Annual cost = (Watts ÷ 1000) × Hours per day × Days per year × Cost per kWh
Example: 6W LED lamp, 8 hours/day, 250 workdays, $0.12/kWh
(6 ÷ 1000) × 8 × 250 × $0.12 = $1.44/year
Comparison across lamp types
| Lamp type | Wattage | Annual cost* |
|---|---|---|
| LED (good) | 5W | $1.20 |
| LED (basic) | 10W | $2.40 |
| CFL/Fluorescent | 13W | $3.12 |
| Halogen | 28W | $6.72 |
| Incandescent | 60W | $14.40 |
*Based on 8 hrs/day, 250 days, $0.12/kWh US average
The dimming multiplier
Run a dimmable lamp at 50% brightness and you roughly halve the power draw. A 10W lamp at 50% draws ~5W. So a $2.40/year lamp becomes a $1.20/year lamp just by using a dimmer. This is why dimmability is an efficiency feature, not just a comfort one.
The “left it on all day” calculation
Forgetting to turn off a 6W LED lamp: costs about $0.0007/hour. Not a disaster. But a 60W bulb left on the same way: $0.0072/hour — 10x more. Smart scheduling eliminates this entirely regardless of lamp type.
Practical bottom line
If you’re already using an LED desk lamp, the energy cost is probably under $2/year. The ROI on upgrading from incandescent or halogen to LED is fast — often under 6 months at regular use. The ROI on upgrading from one LED to a more efficient LED is much slower. Focus the switch on older lamp types, not chasing marginal LED-to-LED gains.
