How to Calculate Power Consumption of LED Lights: A Complete Guide
How do you calculate the power consumption of an LED light? Multiply the wattage by the hours used per day, divide by 1,000 to get units (kWh), then multiply by your per-unit rate. A 12W LED bulb used 5 hours a day uses about 1.8 units a month, which is roughly Rs.90 at an example rate of Rs.50 per unit.
How much electricity does an LED light use? (quick table)
| Light | Units per hour | Units per month (5 h/day) | Cost per month at Rs.50 per unit* |
|---|---|---|---|
| 5W bulb | 0.005 | 0.75 | Rs.38 |
| 12W bulb | 0.012 | 1.8 | Rs.90 |
| 18W bulb | 0.018 | 2.7 | Rs.135 |
| 50W flood light | 0.05 | 7.5 | Rs.375 |
| 100W flood light | 0.1 | 15 | Rs.750 |
*Rs.50 per unit is an example only. Your rate depends on your bill and slab, so check your own electricity bill and replace the number in the formula below.
The formula
Units per month = watts × hours per day × 30 ÷ 1,000
Monthly cost = units per month × your rate per unit
One unit on your bill is one kilowatt-hour (kWh), which is a 1,000W load running for one hour. Because LED lights use so few watts, even a 12-hour day adds little to the bill.
Step-by-step example
- Find the wattage. It is printed on the box and the product page. Example: a 12W bulb.
- Estimate hours per day. Example: 6 hours.
- Daily watt-hours: 12W × 6 = 72 Wh.
- Convert to units: 72 ÷ 1,000 = 0.072 units per day.
- Monthly units: 0.072 × 30 = 2.16 units.
- Monthly cost: 2.16 × Rs.50 = Rs.108. Over a year that is about 26.3 units, or roughly Rs.1,314.
Real examples for a Pakistani home
A whole room or house of bulbs
Ten 12W bulbs running 6 hours a day use 10 × 12 × 6 × 30 ÷ 1,000 = 21.6 units a month, about Rs.1,080 at Rs.50 per unit. Browse our LED bulbs for 5W to 18W options.
Switching from an old bulb
A 12W LED gives about the same light as a 75W incandescent bulb. At 5 hours a day the old bulb uses 11.25 units a month (about Rs.563) while the LED uses 1.8 units (about Rs.90). That is a saving of roughly 84%, which matches the "up to 80% less electricity" figure usually quoted for LEDs.
Outdoor flood lights
Outdoor lights usually run all evening. A 50W flood light running 8 hours a night uses 12 units a month (about Rs.600), and a 100W one uses 24 units (about Rs.1,200). Match the wattage to the area you need to light rather than buying the biggest one: compare the 50W and 100W models, or see all LED flood lights.
Rope and strip lights
For strips, multiply the watts per metre by the length. A 10-metre strip at 5W per metre is 50W, so 8 hours a day is 12 units a month. Our LED rope lights list the wattage on each product page.
Ceiling lights
Downlights and panels are usually 7W to 24W each, so a room with six of them is similar to a few bulbs. See LED downlights and panel lights.
What changes real-world power use?
- Wattage vs brightness: compare lumens, not only watts. A more efficient LED gives more light for the same watts.
- Driver quality: poor drivers waste power and flicker. Voltage swings are common in Pakistan, so a good driver matters.
- Dimming: a dimmable LED uses less when dimmed, but only with a compatible dimmer.
- Hours of use: this is the biggest lever. Switch off in empty rooms.
- Standby power: smart bulbs and drivers can draw a small amount even when off.
How to measure your actual consumption
- Plug-in energy meter: plug the device into the meter to see real watts.
- Smart plug: shows usage in a phone app.
- Your electricity meter: switch everything else off, note the reading, run the light for a few hours and compare.
Tips to lower your lighting bill
- Replace old tube lights and incandescent bulbs with LEDs.
- Use the lowest wattage that gives enough light for the room.
- Use warm white where you want a relaxed light and cool white for work areas.
- Clean fixtures, because dust reduces light output.
- Use timers or motion sensors for outdoor and corridor lights.
FAQ
How many units does a 12W LED bulb use in an hour?
0.012 units (kWh). Used 5 hours a day it uses about 1.8 units a month.
How much does it cost to run a 100W flood light all night?
At 8 hours a night it uses 0.8 units a night, or 24 units a month. Multiply by your own rate per unit to get the cost.
Do LED lights use less electricity than energy-saver (CFL) bulbs?
Usually yes. LEDs normally give the same light for fewer watts than CFLs, and they do not contain mercury.
Does switching an LED on and off a lot use more power?
No. Frequent switching does not use more electricity, and it is better to turn LEDs off when you leave the room.
Does the wattage on the box equal what I pay for?
Your bill is based on the actual watts the light draws multiplied by hours used. The wattage on the box is a good approximation for a quality LED.
Conclusion
Calculating LED power use takes one formula: watts × hours × 30 ÷ 1,000, then multiply by your rate. For most homes lighting is a small part of the bill, and switching to LEDs is one of the cheapest ways to cut it. Explore the full Deltalite LED range or start with LED bulbs.