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The Candela: A Measurement In Flux
Candela is a term that refers to the amount of visible light at any one point, within a specific light pattern.
Candela values measure the intensity of light at a specific location, and this number, just as lumen values, can be used to mislead.
For instance, you could have two different flashlights (Flashlights A and B) that both claim to be 18,000 candelas.
This gives us a general idea of the capabilities of the flashlight but leaves much to be questioned about the performance.
Since candela is the measure of light intensity-not total light output.
Remember, lumen equals total light. Both of these flashlights can claim that they output 18,000 candelas even though they are clearly not performing at the same level.
Flashlight A illuminates half of our subject, as does Flashlight B.
However, Flashlight A is covering a much wider area of our subject at the same candela value as Flashlight B, which means we can assume that Flashlight has a higher lumen value.
Lumen values cannot accurately be converted into candela values (and vice-versa), because they are measures of completely different elements.
Another way to compare candela and lumen values would be to think of pressure-was- and fire hose.
let’s assume our fire hose has a 2-inch diameter barrel and our pressure-washer nozzle head is 1/16th inch.
Now let’s say that both our fire hose and pressure washer are pressurized to 2700psi, or in other words, the water will be flowing out of each hose at the same intensity.
Both hoses are rated at 2700psi, yet, the fire hose displaces much more water overall.
Lumen would be the equivalent of the total amount of water coming out of the hoses and candela would be equivalent to the amount of pressure from where the water is flowing.
A lamp is successful only when it illuminates what it is supposed to be illuminating.
A ball with ten, one-hundred-lumen diodes placed all around its surface would technically be rated at 1000 lumens, but it would make a very poor spotlight.
The Iso -Candela Scan: Putting It All Together
There are many different methods for measuring light.
One of the most accurate tests for measuring the intensity of light within the pattern a lamp produces is known as an Iso-Candela Scan.
The illustration below is an actual Iso-Candela scan from a lamp engineered by New Vision.
There are points of intense light in red; these are often referred to as “hot spots.
We can also see areas of green which are areas of mid-range light that transition out to areas of blue which are areas of very little light.
These colors are simply representational of the light intensity in that area, they have nothing to do with the actual color of the lamp’s light.
Iso-Candela scans are rendered by placing a highly-calibrated tool, known as a Photo-Detector Cell, into a light tunnel along with a light source.
The Photo Detector Cell acts as an eye looking at the light source and is able to transpose the light beams it”sees” the colorful chart you see below
This specific scan shows a head-on angle of a lamp. We can look at the key at the bottom of the image to gauge the candela value for that specific area.
Red is the hottest area with the most intense light, revealing an area is around 16,000 candela; dark blue is the coolest area with the least amount of light, revealing areas of around 25 candelas.
This scan shows the distribution of light as if you were looking directly at it.
Some scans show a bird’s eye view which allows the viewer to see the width and length of light distribution while others examine the light distribution of a lamp from a different angle, i.e., 45.
Notice the hot spot on this scan. This lamp is designed for distance, so the hot spot is very pronounced.
To achieve distance from a lamp one must concentrate the light into a specific area, this concentration creates a hot- spot.
This lamp measured all the way up to 20,000 candelas
In summary, let’s the review:
- Wattage is a measure of power consumed by a lamp, not the light emitted by it
- Lumen value can only be accurately calculated using an integrated sphere, and that there is a difference between Cold Lumen Values and Warm Lumen values
- Candela is a measure of light intensity, not total light output
- lso-Candela Scans measure light intensity and pattern
Light pattern, lumen value, and candela value all play very important roles in LED lighting.
Though it may be tempting to trust a single number on a page, you are now prepared to make a more informed, rounded decision when choosing your next lamp.
