Demystifying Lumens Kelvins & Other Lighting Terms

Demystifying Lumens, Kelvins & Other Lighting Terms

When it comes to understanding lighting terminology, it’s all too easy to feel left in the dark. If you’re confused about which bulb is right for your needs, have no fear. We’ve compiled a comprehensive guide to common lighting terms with the help of Jeff Dross, the Corporate Director of Education and Industry Trends at Kichler Lighting. Highly respected in his field, Dross has over 40 years of experience in the lighting industry and regularly conducts professional workshops all across the country. From lumens and Kelvins to correlated color temperatures, we’re breaking down everything you need to know about the world of lighting.

A Brief History of Light

The earliest artificial light converted nonvisible energy to visible forms of light using wood, oils, coal, and candles. These light sources produced color that was very warm and mimicked the natural beauty of early sunrise and late sunset. Gaslight originated in the early 1800s and utilized open flames to achieve the same effect.

From Edison to Modern Nostalgia (Hover to Toggle)

The first incandescent light was installed in 1880 and created both light and warmth by heating wire filaments via electricity.

The Arc is Born

The first blue-toned artificial light gained ground in the 20th century, when arc discharge lighting was used in streetlamps, searchlights, and movie projectors until the end of World War II.


By 1951, most light in the United States was created by the use of fluorescent bulbs. These lights were three times more efficient than traditional incandescent bulbs and lasted longer, making them an ideal choice for American factories.

Solid-State: LED Arrives

Solid-state lighting (or LEDs) were developed in 2002 using light-emitting diodes to create light. While LEDs started out emitting very blue tones, they have since transitioned to more neutral shades of white.

The Nitty-Gritty

Behind every light design, innovation and breakthrough is science. In lighting, this is where the details really matter. From white light to Kelvins, lumens, Color Rendering Index (CRI) and the Kruithof Curve, each element will help round out your understanding of light.

White Light

Just like natural sunlight, white light is a uniform combination of red, blue, and green wavelengths and contains light from the full visible electromagnetic spectrum. Because of this, white light has no wavelength of its own and instead contains all wavelengths from 390 nanometers to 700 nanometers. Since the color of visible light depends on its specific wavelength, we use two scales to characterize white light: correlated color temperature (CCT) and the color rendering index (CRI).

Kruithof Curve

As lighting technology evolved, researchers began looking at human responses to specific color temperatures and levels of illumination. In 1941, Dutch physicist Arie Andries Kruithof collected psychological data on which colors and illuminance levels were most pleasing to human subjects.

His study found that higher luminance levels are perceived to be more pleasing at higher color temperatures, while lower luminance levels are perceived to be more pleasing at lower color temperatures. This region of visually pleasing light is known as the Kruithof curve. In action, people enjoy being outside in the midday sun when it is bright and blue as they prefer dinner under a dim, reddish candlelit environment. Both of these examples prove what Kruithof discovered.

Color Temperature

A light’s correlated color temperature (CCT) describes its visual appearance in terms of warmth or coolness, and CCT is measured in Kelvins (K). The higher a light’s Kelvin rating, the cooler its overall light. The Kelvin scale ranges from 1000K to 10,000K, but most household fixtures fall somewhere between 2700K (60W incandescent ) and 3000K (halogen). These lower Kelvin ratings are soft, warm, and inviting, whereas high Kelvin ratings are more practical for commercial locations or bright task lighting. Use the chart below to find the right color temperature for your styling preferences and needs:

Pro Tip: Check out our Lamp Buying Guide for tips on choosing the right types of bulbs for table lamps, desk lamps, and floor lamps throughout your home.


For a long time, a light bulb’s overall brightness was measured strictly in terms of watts, but wattage is a measurement of the energy consumed and has nothing to do with the quantity of light. Since LED bulbs naturally have lower watt ratings because they use less energy, it’s important to know the bulb’s lumens rating (lm) to better understand its brightness. In fact, when dealing with wattage (on anything other than incandescent), remember that these numbers are likely to change. As a result, ignoring wattage in lieu of Lumens is highly recommended as it’s the only real indicator of brightness.

"Today, 800 lumens of light can be delivered with as low as 8.5 watts. Last year it was 11 watts and next year it could be down to 8 or 7.5 watts.” says Dross. “It can also depend on the manufacturer. Those using more advanced LED will consume less energy.

Pro Tip: Check out our Light Bulb Buying Guide for more details on selecting the perfect bulb for your unique needs.

Color Rendering Index (CRI)

The color rendering index, or CRI, measures how a specific source of light influences and interprets an object’s color to the naked eye. The CRI scale ranges from 0 to 100 and indicates how accurate a light source is at rendering colors compared to that of a reference light source. The higher a light source’s CRI value, the better it is at distinguishing colors (and the closer it looks to natural sunlight). Incandescent and halogen bulbs render colors exceptionally well, while fluorescent bulbs have a more muted effect.

Pro Tip: CRI measurements of 80 to 90 are considered good, while CRIs of 90+ are considered excellent.

Color Selection

The overall flexibility of LED light makes it easy to choose the color of white light that works best in a specific room. Not only can LED bulbs add color when and where it’s needed, but they also include color options when desired. Contrasting colors fight each other when they’re mixed, which means that yellow light has the unique ability to dull cooler colors while simultaneously strengthening tones with similar warmth. Blue light, alternatively, enlivens dense, cool hues while weakening warm palettes.

Ideal for warm rooms, 2700K LEDs enhance beige neutrals, natural wood, earth tones, and sunny hues like gold, yellow, and orange. Alternatively, 3000K LEDs are a more neutral choice and work well with grey neutrals, blues, purples, greens, and classic black and white. On the other hand, 4000K LEDs are typically best for commercial applications and can beautifully highlight crystal collections and sterling silver displays.

Familiarizing yourself with these common lighting terms can help you illuminate your home to perfection. Check out How to Shop for Energy-Efficient Light Bulbs for more lighting inspiration, and browse our Pro Spotlights series for additional insight from today’s top design influencers.

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