What CFL bulb replaces a 100 watt incandescent?

100W incandescent → CFL

26.7W

both put out about 1,600 lumens — the CFL does it on 26.7 watts

Light outputthis is the number to shop by, not the watts	1,600lumens
CFL wattage needed	26.7W
Incandescent wattage	100W
Efficacy assumedagainst 14 lm/W for a filament bulb	60lm/W
Running cost a year3 hours a day at $0.17/kWh — the incandescent costs $18.62	$4.96
Rated lifeabout 7.3 years at 3 hours a day	8,000hours

Notes

**Buy lumens, not watts.** A watt is what the bulb *consumes*; a lumen is what it *emits*. The habit of shopping by wattage only worked while every bulb was a filament burning at the same efficiency. A 100W incandescent puts out about **1,600 lumens**, and any bulb of any technology hitting that number will look the same brightness.
A CFL reaches 1,600 lumens on about **26.7 watts** because it produces roughly 60 lumens per watt against 14 for a filament. Compact fluorescent — takes a moment to reach full brightness.
**Running cost is where the difference actually shows up.** At three hours a day and $0.17 per kWh, this bulb costs about **$4.96** a year against **$18.62** for the incandescent it replaces. Multiply by the number of sockets in the house before deciding it is a small number.
Packet equivalence claims run a little optimistic — a box marked "60W equivalent" is often 750–800 lumens rather than a clean 800. Check the Lighting Facts panel on the back, which has to print the real figure.
Brightness is only half the choice. Colour temperature decides whether the room feels warm or clinical, and it is independent of both the watts and the lumens on this page.

100W in CFL

A 100 watt incandescent puts out about 1,600 lumens. A CFL reaches the same light on 26.7 watts.

Buy lumens, not watts

A watt is what the bulb consumes. A lumen is what it emits.

Shopping by wattage only ever worked while every bulb was a filament burning at the same efficiency. Once LED and CFL arrived, the same watt buys four to seven times the light — so the habit now picks the wrong bulb.

1,600 lumens is the number to shop by. Any bulb of any technology hitting it looks the same brightness.

Where the difference comes from

A CFL produces about 60 lumens per watt against 14 for a filament bulb. That ratio is the whole story, and it is printed on the box if you look for lm/W.

Running cost is where you actually notice

At three hours a day and $0.17 per kWh, this bulb costs about $4.96 a year.

Multiply by the number of sockets in the house before deciding that is a small number. A twenty-socket house is where the arithmetic stops being trivial.

Check the panel, not the front of the box

Equivalence claims on the front run a little optimistic — a box marked "100W equivalent" is often a shade under 1,600 lumens.

The Lighting Facts panel on the back has to print the real figure, and it is the only number on the packaging that is regulated.

Brightness is only half the choice

Colour temperature decides whether the room reads warm or clinical, and it is independent of everything on this page.

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