How can we compare the light from different types of light bulbs?
In the past, when nearly all light bulbs were incandescent, most people had a general “feel” for how much light you’d get from a light bulb of a particular wattage. For example, most people got used to the idea that you’d need a 100 watt light bulb to make enough light for reading easily, while a 40 watt light bulb might be good for an outdoor porch light. Today, however, we can’t make such direct connections to wattage, because different types of light bulbs (such as incandescent, halogen, fluorescent, LED) have such different efficiencies.
Instead, the better way to compare light bulbs today is by the amount of light they put out, which is measured in units called lumens . The larger the number of lumens, the brighter the light from the bulb. For example, here are the brightnesses in lumens of typical incandescent light bulbs:
- A 100-watt incandescent bulb puts out about 1,600 lumens.
- A 75-watt incandescent bulb puts out about 1,100 lumens.
- A 60-watt incandescent bulb puts out about 800 lumens.
- A 40-watt incandescent bulb puts out about 450 lumens.
Therefore, if you wish to replace a 100-watt incandescent bulb with an LED that gives out the same amount of light, you should look for an LED bulb that is rated at 1,600 lumens. If you do this, you’ll find that the power requirement of such a bulb is typically between about 15 to 25 watts, depending on its quality and manufacturer.