Buying LED lights can be daunting if you are unaware of the units used to measure the light intensity. This is especially true when you are shopping online and do not have anyone to guide you. Candela, Lumens, and Lux are the measuring units commonly seen on the cover of lighting products. Each unit gives valuable insight into the brightness and intensity of the lighting lamp.
These light measuring units may sound confusing, but do not worry; we bring you a complete guide that explains what they are and how they can help you identify the suitable lamp for your project.
We are also going to discuss their relationship. Here is a quick overview for you.
| Lumens | Lux | Candela |
| The total amount of light that a lamp can produce. | The amount of light seen on a surface area of 1 square meter from a certain distance. | It defines the intensity of light produced within a specific angle and direction. |
Candela
Candela is an SI unit (International System of Units) that measures the light intensity source and is represented by “cd.” It is the total amount of light emitted in a specific direction. The directions correspond to the beam angle of the light.
It comes from a Latin word that translates to candlelight and is approximately equal to the light emitted by a single wax candle.
It now has a much more complex definition. For reference, a typical candle emits light equivalent to “1 cd” intensity in all directions. In simpler words, the greater the lamp’s number of candelas, the brighter it will be.
A standard 25 Watts fluorescent bulb emits about 135 cd in all directions, but if the light beam is narrowed down to a 20⁰ beam angle, the intensity increases to ~18000 cd. The narrower the beam angle is, the greater the number of candelas it will produce.
Lumens
Lumen is the most common unit in the market, and it’s often misunderstood. It is defined as the total amount of light emitted by a lighting source in all directions and is denoted by “lm.” Lumens or lumen flux represents the total amount of visible light the human eye perceives. Unlike candela, it is not dependent on a particular direction.
Lumens and candela can be compared. Consider this: a flashlight produces 1 cd of light intensity at a specific beam angle and 12.5 lm of luminous flux. If you block half of the lamp, the same 1 cd source will produce 6.25 lumens. A standard 45 W LED bulb produces about 450 lumens of light. Later in the guide, we will discuss how these units relate and their significance.
Lux
Lux is a derived SI unit for light that defines light intensity in a particular area. Simply put, 1 lux equals 1 lumen per unit area or 1 lm/m2. It’s a helpful unit because it defines a real-life scenario and is easy to visualize. Many photographers use this unit to describe lighting because they are more concerned with light intensity over a specific photoshoot area.
For an observer like you, it means how bright a specific surface area will be when a lamp is illuminated. The light follows an inverse-square law, which states that at triple the distance from the Light source, the Lux would be 1/9th as it is spread over nine times the area.
A light spread over a larger area will have weaker illumination than smaller areas with brighter light intensity. The reflectors in LED fixtures are designed to control light spread over large surface areas to prevent light wastage.
Comparison: Candela Vs. Lumens Vs. Lux
So now you have a basic understanding of units, and you may have concluded that more lumens equals better light. That is not necessarily the case. To choose the best possible light for your project, you need to use a combination of candela, lumens, and Lux.
Why Do You Need to Know About These Units?
We have numerous lighting sources, such as LEDs, fluorescent and incandescent lights, etc. Each source lights the place differently, so to get the best product for your project, you need to consider all of them. This will come in handy when designing the lighting for the place.
How to Measure Light Using These Units?
The luminous intensity of the light sources is quite difficult to measure, and it is done in specified research laboratories. The manufacturers then mention the values on the cover of the lighting product. Using the information presented here, you can compare values between different lighting products.
1. Lumens and Candela- How Do These Relate?
Lumens are used for luminous flux and are mainly used by manufacturers to define the raw potential of the light source. A fixture labeled 100 lm indicates the lamp can produce this much light in all directions.
It has nothing to do with the design and geometry of the product. How are the reflectors placed, and what intensity will you receive in a particular direction? That is why lumens refer to only the rating of bulbs. It does not give a complete picture of the luminous potential of a light source. So, you may have to keep that in mind. Consider the below picture for a better understanding.
When lumens refer to the total raw potential output of the Light, the candela, on the other hand, defines the intensity of the same light in a particular direction and an angle. It captures the volume and power of the light.
The angle is defined as a steradian, a three-dimensional angle formed in the sphere by opening a cone and projecting the area equal to the square of the radius. Below is the area that corresponds to one candela.
A high candela rating is useful if you want to focus light on something, especially in art galleries, spotlights, facades, vehicle headlights, etc. One candela is equal to one lumen per steradian, so the relationship between Lumens and Candela is easy to remember.
1 Candela= 12.57 Lumens
However, it is not advisable to compare the candela to lumens directly. The regular laser light would have a very minute lumen value but a large candela rating.
2. Lumens and Lux- How Do These Relate?
If you choose two LED lamps with a similar 100 lumens rating, they will not necessarily have the same brightness. Why is that? We have not considered the reflectors and fixtures’ design.
This is where Lux comes in. Lux is a useful and practical light-measuring unit defining the light amount on a specific surface area. It is estimated to be about 10 meters away within 1 square foot of the wall. The picture below gives insight into how an area of one square meter is illuminated, which equals 1 flux.
1 Lumen= 1 Lux per square meter
Consider a Spotlight; it will have a large Lux value because it concentrates within an area and throws the light to longer distances. A spread light will cover a much larger surface area and have a low Lux value, even though it may have around the same lumens as the spotlight. The design and engineering of the fixture control this factor. Now you know the importance of the right Lux value.
Many conversion calculators are available online to convert values between candela, lumens, and Lux with some approximations.
Foot candles
It is a non-SI illuminance unit, similar to Lux, which defines it by an area. One lumen per square foot equals one ft-candle. This unit is not as important as others but is used for lighting layout in some parts.
3. Lumens and Watts- How Do These Compare?
If you have visited a lighting store, you will surely have seen the word watts for a lamp. It is often misunderstood. It is not a unit for measuring light and is used to define the power consumed by a lamp, denoted by “W.”
A 1 W LED will produce more light (lumens) than a 1 W halogen light. This is because LEDs are much more energy-efficient. Greater wattage consumption means greater heat production, which results in significant energy loss. To get the gist of the comparison, here is some reference for you:
| Watts | Lumens |
| 40 | 450 |
| 60 | 800 |
| 75 | 1100 |
Luminous Efficacy
Luminous Efficacy is the efficiency that defines how well a source produces light. It is given by luminous flux per power consumed OR simple Lumens/Watts. A greater efficacy results in brighter light.
Which is the Best Measuring Unit for Light?
It depends on your usage. Larger lumen-rated lamps would be great for lighting up a room. Higher candela and lux values should be your priority if you want to highlight architectural features or focus on something. Consider your business project and what objectives you want to achieve, and using the above guide, you can purchase optimal light.
Conclusion
Choosing an LED is not difficult if you consult an expert LED manufacturer. Let us know your needs, and we will guide you to the exact lighting requirements for your projects! For more information, contact RC Lighting.
