Warm White or Cool White: How Do I Know the Right Light Temp/Color to Choose?

With all the new choices in LED and energy-efficient lighting, color temperature (° Kelvin) and CRI (Color Rendering Index) often seem to be the most confusing to people. What is the difference between warm white and cool white, how do I choose the right color temperature for the task?
Color Temperature Changes throughout the Day
Photo Credit: Verbatim.com

The Kelvin Scale Represents Light Color Given Off by Hot Iron
Firstly, it helps to understand what the Kelvin scale represents. Imagine you’re a blacksmith, as you heat a piece of metal (iron to be precise,) it begins to glow. At 2200°f, the metal glows red hot and if removed from the fire, it will radiate an orangey glow, a piece of white paper exposed to this light source will appear orange. Perception of color changes as you rise through the Kelvin scale. Around 2800-3,200 Kelvin or 3200°F, the metal glows a fiery orange-white. This is the approximate color temperature of standard incandescent lights, in fact the filament inside the light bulb is actually reaching these temperatures. Let’s increase the temperature to 5000°, the metal now radiates an almost pure white light, raising the temperature even higher emits more blue spectrum and around 8000° K. is very similar to natural daylight.

When to Choose Warm White
Although a matter of preference, warm white (2800° Kelvin) is most often found in living rooms, and commonly used in relaxing areas, warm white simulates the coziness of fire, or candlelight. Warm white has been found to enhance the look of wood, and is more often the choice for cabinets and highlighting carpentry and wood-work.

Warm white is the appropriate choice for lighting areas that will be utilized in the evenings.

Went to Choose Cool White
Cool white very closely resembles natural light entering a window on a cloudy day. Cool white tends to be the most efficient in the Watts to lumen output (LED); choosing cool white often results in a 10 to 15% efficiency increase. If brightness is your goal, Cool white may be the choice for you. Color temperatures of 7000° may appear “Icy or Cold” especially in the evenings.

Cool White is Excellent Task Lighting
Cool white is synonymous with productivity; there is a reason why 6000° K. high output florescence are popular in office buildings, because warm colors trigger feelings of relaxation, while cooler colors invoke the productivity of natural daylight. Choosing lighting in the 4000° to 7000° K. may appear slightly bluish in the evening, but when mixed with natural light blends in fairly seamlessly.
Cool white is the preferred color temperature for highlighting natural rock features; slate, granite and other stone surfaces. Cool white is sometimes also preferred for task lighting in kitchens.

What You Need to Know About CR I (Color Rendering Index)

The CRI scale (sometimes called color rendition index) is a 1 to 100 rating system, based on how realistic colors appear under different light sources. Orange streetlights (high-pressure sodium HID lamps) emit an orange tinted light, with a little Kelvin temperature of 2100° therefore qualifying for a rating of -24- on the CRI. Cool White fluorescent has a color rendering index of approximately -64- with the Kelvin temperature of 4200°
As an example: a museum would be very concerned with the color rendering index, they would desire as close to 100- as possible so colors are most accurately represented. While parking lot lighting, is designed more for lumen output than any consideration of what color your white car appears to be.

When choosing LEDs CRI and color temperatures, consider the application, warm white for cozy indoor situations and cool white for safety and task lighting.

Lighting with a color rendering index of 70 or lower may be fine for security or safety lighting, but if decisions are being made based on the appearance of certain colors (looking at paint chips) be sure to choose lighting with a CRI of 80 or higher.
New products being introduced, can change Kelvin temp on command or when dimmed.

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