Lumens Vs Candela: Science is Hard

What are the basics?
Candela and lumens are both units of measurements for light. However, each measures different aspects of lighting. Knowing the difference will keep you from being misled by manufactures who advertise impressive numbers of lumens or candela that may not be relevant to your use.

Defined
Lumens are a measure of the total amount of visible light emitted by a device. Lumen is currently the most common unit of measurement for a bulb and is a rating of how much total light is produced.

Candela is known as candlepower. What a throwback. This refers back to when the candle was the primary source of light, other than the sun. It is the measurement for luminous intensity, the brightness of the light.

How are they different?
The difference can be explained as follows: Say one person is holding a flashlight and another is holding a light bulb. The bulb will have higher lumen value because it spreads a greater amount of illumination over a larger area than the flashlight. The flashlight will have a higher candela because its light is focused into a single direction with higher intensity. For example, a laser pointer will have a low lumen measure but a high candela value. The laser doesn’t emit much light but is concentrated into a beam that can be seen over a greater distance.

Real-world use
Since the two measure different aspects of illumination, it is important to compare lighting devices using the same unit of comparison. When shopping for a particular light, keep in mind your intended use of the light, and compare the same measure accordingly. This will ensure you make the best purchasing decision. Remember, lumens measure how much light is emitted, and candela measures the intensity of the light.