When selecting lighting for commercial, industrial, or public buildings, get help from a quick guide to Kelvin vs. lumens. Understanding light quality as defined by these two different measures can help you choose the most effective and beneficial lighting for your business.
These two metrics influence the ambiance and functionality of a space and contribute significantly to energy efficiency and user comfort. Demystify these terms by learning what they measure and why they're essential for making informed lighting choices.
Where Did “Kelvin” Come From?
The Kelvin scale is named after William Thomson, 1st Baron Kelvin, a physicist who contributed significantly to the development of the thermodynamic temperature scale. While Kelvin's work was primarily in thermodynamics, the unit that bears his name has become a critical measure in the realm of lighting, particularly in specifying the color temperature of a light source.
What Is Color Temperature?
One common misconception about the Kelvin scale in lighting is that it refers to the heat emitted by a light bulb. However, color temperature describes a light source’s color appearance to the human eye. The Kelvin scale allows users to understand the light’s hue as warm or cool, which plays a significant role in setting the mood and functionality of a space.
The Concept of a Black Body in Relation to the Kelvin Scale
A black body is a theoretical object that perfectly absorbs all electromagnetic radiation (light) that falls on it without reflecting any back, making it crucial in the study of electromagnetic radiation and temperature. In relation to the Kelvin scale and lighting, a black body is the standard theoretical reference used to describe the color temperature of light.
When heated, a black body emits a spectrum of colors ranging from red to orange, yellow, white, and then blue as its temperature increases. The color temperature, measured on the Kelvin scale, corresponds to the hue emitted by a black body at a certain temperature.
For example, a light source with a low Kelvin value emits a warmer, reddish light, similar to what a black body would emit at a lower temperature. A higher Kelvin value corresponds to a cooler, bluish light, mimicking a black body at a higher temperature. This relationship helps to quantify the warmth or coolness of light sources in a way that's easy to understand and apply in lighting design.
The Kelvin Scale’s Range
The Kelvin scale ranges from about 1,000 to 10,000 K. Contrary to what one might expect, lower Kelvin values (around 2000K to 3000K) indicate warmer light colors, such as red, yellow, and orange, like the hues observed at sunrise or sunset. These warm lights create a cozy and relaxed atmosphere, often used in residential settings or restaurants to evoke a sense of comfort.
Higher Kelvin values (5000K to 6500K) correspond to cooler light colors like blue and bright white, which are more reminiscent of daylight. People perceive cooler light as brighter, and businesses typically use it in commercial and industrial settings where tasks require clear visibility and concentration.
Color temperature influences the perception of brightness. Light sources with a higher Kelvin rating can seem brighter to the human eye than their warmer counterparts, even if their actual light output is the same. This phenomenon is crucial for lighting designers and specifiers to consider when choosing lighting for different applications.
What Is the Color Rendering Index (CRI)?
CRI is a metric used to describe how accurately a light source reveals the true colors of objects compared to a natural light source, such as sunlight. The scale measures the index from 0 to 100, with higher values indicating better color accuracy. A CRI of 100 equates to the ability of sunlight to accurately render color.
Incandescent lights have a CRI of 100, whereas most LEDs have CRI ratings between 80 and 90. It’s important to understand that Kelvin scale ratings don’t correlate to CRI ratings. You can have a warm LED with a high CRI or a cool LED with a low CRI, so be sure to check descriptions to determine how a particular bulb renders color.
Why CRI Matters for Commercial, Industrial, and Retail Spaces
In retail environments, lighting with a high CRI ensures that customers can see products in their true colors, making them more appealing. This is crucial in stores selling items like clothing, furniture, or artwork, where color differentiation and accuracy can influence purchasing decisions.
For industrial and commercial spaces, such as factories or offices, lighting with a high CRI can improve workers' ability to perform tasks accurately and safely, particularly in operations requiring color discrimination and detailed work.
High CRI lighting can also enhance the ambiance of a space, making it appear more vibrant and true-to-life. This is particularly important in spaces like museums and galleries, where accurate color representation can significantly impact the visitor experience.
What Do Lumens Measure?
While Kelvin helps define the color characteristics of light, lumens measure the amount of visible light a source emits. In simple terms, lumens quantify the brightness of a light bulb or fixture, indicating how much light you can expect to fill a space.
From Watts to Lumens
Traditionally, light bulb brightness was gauged by its wattage, a measure of its power consumption. However, with the advent of energy-efficient lighting technologies such as LEDs, using watts to infer brightness became less practical. LED lights consume significantly less power (watts) while producing the same, or even greater, light output (lumens) compared to incandescent or halogen bulbs. Consequently, lumens have largely replaced watts as the go-to metric for evaluating light output.
For example, an LED bulb may only use 10 watts of energy but can produce the same amount of light (in lumens) as a 60-watt incandescent bulb. This disparity underscores the importance of lumens in assessing the true brightness of a lighting fixture, independent of its energy consumption.
Wattage Equivalencies and LEDs
Many LED products include wattage equivalency labeling to help consumers understand how their light output compares to traditional incandescent bulbs. This reference is particularly useful during the transition period as more users shift from familiar incandescent lighting to LEDs. By focusing on lumens, users can more accurately select LED lighting that meets their brightness requirements without over- or under-lighting a space.
Why Kelvin, Lumens, and CRI Matter
Kelvin and lumens are important to understanding light quality when choosing lighting for commercial, industrial, or public buildings. The color temperature (Kelvin) affects the mood, appearance, and usability of a space, influencing everything from consumer behavior in retail settings to productivity in offices.
Lumens ensure that a space is bright enough to meet its intended purpose, while avoiding blinding glare or overpowering the space. Kelvin ratings and lumens are relevant for showcasing merchandise, facilitating focus and work, or ensuring safety in public areas. Choosing lighting that balances the right color temperature with adequate brightness enables designers and facility managers to create environments that are not only energy-efficient but also conducive to the well-being and satisfaction of the occupants.
CRI is important to ensure that the lighting you choose can render colors as they would appear in natural sunlight. This is particularly crucial in instances where accurate representation of color is critically important.
Kelvin scale ratings and lumens are vital considerations when choosing lighting. CRI helps you understand whether colors will look correct when illuminated by the chosen lamp. Understanding these measures guides building managers in creating spaces that are visually comfortable, functionally appropriate, and energetically sustainable. From LED corn bulbs for exteriors to bright linear or high bay LED lights and cozy restaurant lighting, facility managers and designers can create ambiance, ensure safety, and accurately represent products and ingredients.
