Most of us have stood in the lighting aisle trying to figure out which bulb to buy. For decades, the number we looked at was watts (W). A “100W bulb” was known to be brighter than a “60W bulb.” But here’s the catch: watts measure power consumption, not brightness.
Today, the better number to look at is lumens (lm), which measure how much visible light the bulb actually produces. The higher the lumens, the brighter the light.
Power vs. Energy: The Engineering Difference
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Power (Watts, W) = how much energy a device consumes at a given moment. Think of it like the flow rate of electricity.
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Energy (Watt-hours, Wh) = how much electricity is used over time. This is what you’re billed for on your electricity bill.
Example: A 10W LED bulb running for 10 hours uses 100 Wh (0.1 kWh) of energy. A 60W incandescent bulb running for the same 10 hours uses 600 Wh (0.6 kWh).
Both might give you similar brightness, but one uses 6 times more energy.
Lumens vs. Watts
Because people used watts as a proxy for brightness in the past, it’s easy to see why confusion exists. But watts alone only tell you how much electricity is being drawn—not how much light you’ll actually get.
That’s where luminous efficacy comes in:
Luminous Efficacy = Lumens ÷ Watts
It measures how efficient a light source is at turning power into visible light. Different bulb types vary significantly:
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Incandescent bulbs: ~15 lumens per watt
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Halogen bulbs: ~20 lumens per watt
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Compact Fluorescent (CFL) bulbs: ~70 lumens per watt
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LED bulbs: ~80–110 lumens per watt (and climbing higher with new tech)
So, at the same wattage, an LED produces many times the light of an incandescent.
How to Choose the Right Bulb
Here’s a quick rule of thumb from the U.S. Department of Energy:
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Replace a 100W incandescent with a bulb that provides ~1,600 lumens
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Replace a 75W incandescent with ~1,100 lumens
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Replace a 60W incandescent with ~800 lumens
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Replace a 40W incandescent with ~450 lumens
(Source: energy.gov – Lumens and Lighting Facts Label)
The Bottom Line
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Watts = Power consumed (what the bulb draws).
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Lumens = Light output (what the bulb gives).
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Energy (kWh) = Power × Time (what you pay for).
Next time you’re choosing a bulb, don’t just think about watts—look at lumens for brightness, and watt-hours for efficiency over time.
And if you have questions about choosing the right LED solutions for your home or business, Big Shine LED is here to guide you.
