Candela vs. Lux vs. Lumens

You've got a light that just blinked out at home. After checking the pantry and your garage, you realize that you're out of light bulbs to use. That means it's time to visit the store or start shopping online.


As you pick up the product or read the manufacturer's description, you start finding different terms. One offers information about candela, another talks about lux, and there are lumens out there to consider.


Why doesn't the industry use the same term to measure what you need to know when purchasing new bulbs?


Instead of taking your best guess at what a product offers, this guide takes a closer look at what you can expect when encountering these terms.


What Is Candela?

Candela is often seen as a candlepower or “CD" rating for lights. It's the base measurement used to determine the product's luminous power intensity. It lets you know how bright the light is based on how far away you are while still seeing it.


Candlepower and horsepower are structured similarly from a measurement point of view. If one horsepower is equivalent to the performance of a single horse, one candlepower equals the light output from a single candle.


Any light eventually becomes too dim to see when you're far enough away from it. That means the CD rating is different from lumens because you're looking at an intensity rating vs. a total light output measurement.


Products like spotlights and laser pointers tend to have the industry's highest candlepower rating because most of the illumination focuses in a single direction. Even if you block a portion of the light, the same intensity is seen from the areas that aren't obscured.


What Is Lux?

When a light bulb promotes its lux rating, that means you're seeing a measurement of illuminance. That's the amount of light within a specific per-unit surface area.


If you're looking at lux vs. lumens, a single lux is equivalent to one lumen within a square meter.


Lamps displaying lux measurements for brightness usually list a distance from the bulb as part of the information. That info is necessary because any proximity alterations change the perceived lux level.


If you have a spotlight that shines only in one square meter with a 500-lumen rating, the surface area has a 500-lux rating.


Now let's say the spotlight gets backed up so that it now shines over five square meters. Even though the lumens stay the same (500), the lux rating decreases to 100 because of the extra space that requires illumination.


Although this information isn't always helpful for indoor lighting needs, it does provide data about replicating daylight inside or providing appropriate task light installation.


Full daylight delivers up to 25,000 lux, while moonlight offers one.


What Are Lumens?

Most light bulbs offer measurements in lumens today. This information provides data about how much luminous flux is available in the product, referring to its total visible light.


When candela ratings remain the same when light becomes obscured, a lumen rating decreases because less total light is available.


Imagine having a light bulb turned on with a 3 CD rating. That product would provide approximately 38 lumens when it offers uninterrupted illumination.


Let's say that half of the bulb gets obscured, leaving a single hemisphere to provide illumination. The 3 CD rating remains unchanged because the parts left unobscured are still visible from the same distance.


If you measured the lumens in that situation, it would cut the rating by 50%. That's because you're only looking at the visible light from the source.


How Many Lumens Is in a One Candela?


How bright is a candela?


One candela equates to 12.57 lumens. Trying to compare these two information points to find the right light bulb is like comparing horsepower to speed for an automobile.


Although one engine might have a stronger HP rating, both can eventually reach 60 miles per hour.


Candela and lumens measure different intensity aspects. Trying to compare one with the other information between two products won't provide an accurate result. You'd want to compare two candela or two lumens ratings.


This principle also applies with lux comparisons to lumens and candela.


How Bright Should Indoor Lights Be Today?


When you have that light bulb to replace, the goal should be to replicate or increase the amount of illumination and brightness you receive. That's why understanding the candela vs. lux vs. lumens ratings is crucial to the comparison process.


Most light bulbs provide measurements in lumens today, including most of today's energy-efficient LED bulbs. A higher number indicates that you'll receive more brightness in the fixture's environment.


Each room has different requirements. Most people want more light in the bathroom or kitchen and less brightness in a bedroom or entertainment area.


You'd look for a lumens rating that equates to about 70 lumens per square foot in bathrooms and kitchens. If you have 100 square feet, you'd want 7,000 lumens provided in that space. Since one 7,000-lumen bulb isn't practical, the total fixture count must also be considered.


If you have four fixtures in the kitchen, you'd want a bulb that offers 1,750 lumens.


About 20 lumens per square foot in bedrooms and other spaces are considered an acceptable rating. In 100 square feet, you'd want up to 2,000 lumens available. Since that's more practical with a single bulb, you can accordingly shop for what you need.


How to Remember the Candela vs. Lux vs. Lumens Differences


Every light contributes to the candela, lux, and lumens ratings achievable in that space. From accent to task lighting, you'll want to consider each specific need to understand what to install or use as a replacement.  


Here's an easy way to remember the different ratings so that you get the correct bulbs for your space.


  • Candela measures the levels of visible light intensity from the source.
  • Lux describes how bright surfaces are once the bulbs are correctly installed.
  • Lumens looks at how much light occurs within the environment.


Once you know those descriptions, finding an appropriate replacement solution is much easier.



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