Light Bulb Replacement Calculator
Turn bulb count, daily hours, and bulb life into yearly hours and replacements.
What it does
Bulb shopping is really buying hours of light. A bulb burning 5 hours daily runs 1,825 hours yearly, so a 15,000 hour LED lasts about 8 years while a 1,000 hour incandescent lasts months.
The tool above takes bulb count, daily hours, and rated bulb life. It returns yearly hours, life in years, and yearly replacements, so 20 LEDs at 5 hours read as 2.43 swaps a year.
This math fits steady daily use with one life rating. It does not fit dimmed circuits, enclosed fixtures that run hot, or mixed bulbs with different ratings in one count.
Energy data frames the same base: lighting sits among the top home electricity uses, with consumption surveys tracking equipment and hours. Longer rated life cuts both swaps and energy per lumen.
Read the box life before stocking spares. Two spare LEDs cover years for most rooms, while short life bulbs want a shelf pack.
How to use
- Count bulbs sharing the same schedule.
- Enter average hours each burns daily.
- Enter rated life hours from the box.
- Read yearly hours first for the use line.
- Read life years for the swap horizon.
- Read yearly replacements for the spares budget.
Formula
- hours
- Average burn hours per bulb daily.
- life
- Rated bulb life in hours from packaging.
- bulbs
- Count sharing that schedule.
Same schedule must apply to all counted bulbs. Short life ratings give fractional years below one. LEDs often rate 15,000 hours and up, older types near 1,000.
Worked example
Example: 20 bulbs, 5 hours a day, 15,000 hour life
Bulbs 20, hours per day 5, life 15000 hours.
- Yearly: 5 x 365 = 1,825 h.
- Years: 15000 / 1825 = 8.22 years.
- Replacements: 20 / 8.22 = 2.43 bulbs/yr.
- Tool shows 1,825 h, 8.22 years, 2.43 bulbs/yr.
- Stock: 3 spares cover the coming year with margin.
Reference table
| Life rating | Life years | Per year |
|---|---|---|
| 1,000 h | 0.68 years | 14.60 bulbs/yr |
| 15,000 h | 10.27 years | 0.97 bulbs/yr |
| 25,000 h | 17.12 years | 0.58 bulbs/yr |
Limits
- One schedule per run. Mixed rooms need separate lines.
- Rated life only. Heat and dimmers shift real life.
- Ignores lumen loss before full burnout.
- Ignores energy cost, which needs wattage too.
Common mistakes
- Mixing bulb types with different life ratings.
- Using peak holiday hours as the daily average.
- Reading life years as a warranty promise.
- Forgetting spares for short life utility bulbs.
- Comparing replacements without matching bulb counts.
Try it yourself
Quick checks. Answers sit tucked under each question.
10 bulbs, 3 hours a day, 1,000 hour life?
1,095 h a year, 0.91 years life, 10.95 bulbs/yr.
12 bulbs, 4 hours a day, 25,000 hour life?
1,460 h a year, 17.12 years life, 0.70 bulbs/yr.
6 bulbs, 6 hours a day, 15,000 hour life?
2,190 h a year, 6.85 years life, 0.88 bulbs/yr.
Questions
How long will my bulbs last?
Divide rated hours by yearly hours. 15,000 hours at 1,825 a year is 8.22 years.
How many replacements a year?
Bulbs divided by life years. 20 bulbs at 8.22 years need 2.43 a year.
Why do LEDs last longer?
Higher rated hours, often 15,000 and up versus about 1,000 for old incandescents.
Do dimmers change this?
They can. Heat, dimming, and enclosed fixtures shift real life from the box rating.
How many spares should I keep?
Round yearly replacements up. 2.43 a year means 3 spares.
Does this cover energy cost?
No. Add wattage and rates for dollars; this page counts swaps only.