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.
What Affects Candela Value?
The same light source can show very different candela numbers depending on how its light is shaped and directed. Here are the main factors that push that value up or down.
Beam angle
Beam angle has the biggest impact. When you squeeze the same amount of light into a narrower cone, all that output is packed into a smaller area, so the intensity in that direction climbs sharply. 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.
Reflector design
Reflectors and mirrors sit behind or around the light source and bounce stray light forward into the useful beam. A well-shaped reflector “recycles” light that would otherwise scatter sideways, concentrating it in one direction and raising the candela value. The precision of the reflector’s curve and its surface finish both play a role—a polished, accurately shaped reflector delivers a tighter, more intense beam.
Lens and optics
A lens bends light through refraction to either focus or spread the beam. A focusing lens tightens the beam and increases candela; a diffusing lens spreads it out and lowers candela. Many modern LED fixtures use TIR (total internal reflection) lenses to control beam angle precisely without wasting light.
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.
What affects a light source’s lumen output
Two products with the same wattage can deliver very different lumen numbers. Here’s what drives that difference.
Light source type
Different lighting technologies convert electricity into light with different efficiencies, a property called luminous efficacy (measured in lumens per watt). LEDs typically deliver far more lumens per watt than fluorescent or incandescent sources, which is why a low-wattage LED can outshine a much higher-wattage traditional bulb.
Power (wattage)
Within the same technology, higher power usually means more lumens. But wattage only tells you energy consumed, not light produced—always compare lumens, not watts, when judging brightness.
Lumen depreciation
No light source stays as bright as it was on day one. Output slowly fades with hours of use, a process called lumen depreciation. This is why LED products are rated with an “L70” value—the point where output drops to 70% of the original—so buyers know the usable lifespan, not just the initial brightness.
Heat and thermal management
Higher operating temperatures reduce light output and speed up depreciation. Fixtures with good heat sinking and airflow hold their lumen value longer, which matters most for high-power or enclosed installations.
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.
What affects the lux on a surface
Since lux describes brightness on a real surface, several practical factors decide the final number you measure.
Distance from the light source.
Light follows the inverse-square law: at triple the distance from the source, the lux drops to 1/9th, because the same light now spreads over nine times the area. In short, light spread over a larger area is always weaker than the same light concentrated on a smaller one.
Mounting height.
The higher a fixture is installed, the wider its light spreads before reaching the surface, lowering the lux at working level. This is why high-bay warehouse lights need far more lumens than a desk lamp to hit the same lux target.
Beam angle and reflectors.
LED fixtures use reflectors and specific beam angles to control where the light lands and prevent waste. A narrow beam concentrates lumens onto a small area for high lux, while a wide beam spreads the same output thin—so matching the beam angle to the mounting height is what determines usable lux, not the raw lumen rating alone.
Surface reflectance.
Light-colored walls, ceilings, and floors bounce light back into the space, while dark surfaces absorb it. The same fixtures can deliver noticeably higher lux in a room with reflective finishes.
Number and layout of fixtures.
Lux at any point is the combined light from every fixture reaching it. Proper spacing prevents dark gaps and uneven pools of light, giving consistent illuminance across the whole area.
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.
Real-World Applications: Which Unit to Check First for Your Project
Knowing the definitions is one thing—knowing which unit to check first for your project is what actually saves you money. Here’s how the three units map to real commercial applications.
When Lumens Matter Most
Lumens tell you the total light output, so they matter when you need to fill a whole space evenly rather than aim light at one spot.
- Offices: Enough overall output to reduce eye fatigue, without harsh bright-and-dark zones across desks.
- Retail stores: Uniform ambient lighting so customers can see product details clearly anywhere in the aisle.
- Hospital corridors and waiting areas: Even general lighting that avoids sharp light-to-dark contrast, which helps prevent trips and falls.
Quick tip: If your main question is “Is the whole room bright enough?”, start with lumens.
When Candela Matters Most
Candela tells you intensity in one direction, so it matters whenever you need to aim, focus, or throw light a long distance.
- Stage and studio lighting: Follow spots need high candela to hold a tight, sharp beam on a performer from far away.
- Art galleries: Directional intensity is adjusted to each exhibit so visitors see detail without glare or wash-out.
- Restaurants: Narrow-beam accent lights raise the candela on the table to make dishes look more appealing.
- Data centers: Aimed high-candela light picks out cable ports and cabinet labels precisely.
Quick tip: If your question is “Can I focus a strong, defined beam exactly where I want it?”, look at candela.
When Lux Matters Most
Lux tells you the actual brightness landing on a surface, so it matters when a standard or task defines how bright the work surface itself must be.
- Warehouses: Lux at floor and rack level drives visibility, picking accuracy, and worker safety.
- Schools: Classrooms, labs, and libraries have recommended lux targets for reading and writing—typically around 300–500 lux for general classrooms.
- Sports facilities: Stadium standards are written in lux because player visibility and broadcast quality depend on illuminance on the playing surface.
Quick tip: If your project has a compliance target or task-level requirement, lux is the number you’ll be measured against.
Which is the Best Measuring Unit for Light?
You rarely rely on just one unit. A practical shortcut:
- Start with lux to define how bright the surface needs to be (often set by a standard).
- Check candela if the light must be aimed or focused.
- Use lumens to confirm the fixture produces enough total output to reach that lux target at your mounting height.
One of the most common mistakes buyers make is comparing two fixtures by lumens alone. Two lamps rated at the same lumens can deliver very different lux on the floor, depending on beam angle and mounting height. Always ask for a fixture’s beam angle—or better, a photometric report—before comparing products.
Frequently Asked Questions
What is CRI, and does it affect lumens or lux?
CRI (Color Rendering Index) measures how accurately a light source shows the true colors of objects, on a scale of 0 to 100. It is a separate metric from lumens, candela, and lux—a fixture can be very bright but still have a low CRI, making colors look washed out or unnatural.
This matters most in retail displays, art galleries, hospitals, and print or paint work, where accurate color is critical. When comparing two fixtures with similar lumen or lux ratings, always check the CRI as well. For most commercial spaces, look for a CRI of 80 or higher; for color-critical tasks, aim for 90+.
How do I convert lux to foot-candles, and when would I need to?
Foot-candles and lux both measure illuminance on a surface—the difference is only the unit of area. One foot-candle equals roughly 10.76 lux (or a rough working figure of about 10). To convert lux to foot-candles, divide by 10.76; to go the other way, multiply.
You’ll usually need this when working with lighting standards or specifications written in the older imperial system, common in parts of North America. Many local building codes, warehouse specs, and sports-facility guidelines still list requirements in foot-candles, while product datasheets often report lux—so knowing the conversion prevents costly design errors.
Does color temperature (Kelvin) change how bright a light looks?
Yes.Perceived brightness and measured brightness aren’t always the same. Two fixtures with identical lumen ratings but different color temperatures (measured in Kelvin) can feel different to the human eye. Cooler light (around 5000–6500K) often appears brighter and crisper, while warmer light (2700–3000K) feels softer and dimmer, even at the same lux level.
This is why lux targets alone don’t tell the whole story for comfort. For task-heavy spaces like warehouses and workshops, cooler temperatures aid alertness and detail work; for hospitality and residential settings, warmer tones create a more comfortable atmosphere without needing more raw output.
What should I do if no off-the-shelf fixture matches my project’s lux, beam angle, and mounting requirements?
This is more common than most buyers expect. Real projects often have unusual ceiling heights, specific compliance targets, or mixed lighting zones that standard catalog products don’t cleanly cover. Trying to force a stock fixture to fit can lead to over-lighting, dark spots, or wasted energy.
In these cases, a custom lighting solution is usually the better route. A manufacturer can adjust beam angle, output, optics, color temperature, and housing to hit your exact lux target at your specific mounting height—backed by a photometric report that proves performance before you order. If your project has requirements that off-the-shelf products can’t meet, contact RC Lighting to discuss a custom lighting solution tailored to your specifications.
Conclusion
Candela, lumens, and lux each answer a different question. Lumens tell you how much light a fixture produces in total, candela tells you how intense that light is in one direction, and lux tells you how much of it actually lands on your working surface. Watts, meanwhile, only tell you energy consumption—not brightness.
Once you understand how these units relate, comparing products becomes far easier. You stop judging fixtures by lumens or watts alone, and start matching beam angle, mounting height, and required lux to the real needs of your space—whether that’s an office, a warehouse, an art gallery, or a sports facility.
The key takeaway: the “brightest” fixture on paper isn’t always the right one for your project. The right unit to check first depends on what you’re trying to light.
If you’re planning a project and want to make sure your fixtures hit the correct targets, our team can help. Let us know your needs, and we will guide you to the exact lighting requirements for your projects! For more information, contact RC Lighting.
