Jul 03

How much light is 100 Watts?

Just how much light does a 100 Watt light make? The answer is “it depends”.

Watts are not a measurement of light. Watts define how much power the light uses to make light. In a typical ‘old-fashioned’ incandescent light bulb you’d buy for a dollar at the hardware store, a “100 Watt” bulb will produce on average 1200 (typically 1100-1300) lumens. Lumens are the measurement of quantity of light produced by a light bulb. This means that a typical incandescent light bulb has a light efficiency rating of: 1200 Lumens divided by 100 Watts = 12 Lumens per Watt

In the past few years Compact Fluorescent Light bulbs (CFL’s) and Light-Emitting Diodes (LED’s) have become very popular because they produce light more efficiently than traditional incandescent bulbs.

Typical Comparison Table


Bulb Type Typical Lumens Comparable Wattage Typical Efficiency
Incandescent 1200 100 12 Lumens/W
CFL 1000 15 67 Lumens/W
LED 1200 10 120 Lumens/W
Bulb Type Expected Lifetime Average Cost Cost to Run per 2000 hours
Incandescent 2000 hours $1 $1.40
CFL 10,000 hours $5 $0.25
LED 50,000 hours $20 $0.14


In a nutshell, CFL’s are more efficient (less expensive to operate) that incandescent. From a purchasing perspective, they are comparable in price, since they cost 5 times more, but last 5 times longer.

LED’s are more efficient than both incandescent and CFL. Because of their extremely long lifecycle, they are also less expensive to purchase, and you’ll rarely (if ever) have to change a light bulb again!

FYI – Light also has a measure of color spectrum which is called Kelvins, but that’s a topic for another day…