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Who's Kelvin, And Why Does This Light Make Me Look Bad?

September 28, 2015


Trying to find the right light bulb can bend your mind like finishing a Rubik’s cube.  Incandescent, CFL, LED, Edison screw-in or pin-based?  And who the heck is “Kelvin,” anyway?  We all want light that’s pretty, and yeah ‘makes us look good.


Even though we have lots of options today, one thing to remember is that there’s something primal about light.  Through the millennia, humankind has become hard-wired to draw near glowing campfires, or later, roaring fires in fireplaces.  Fire warms us, feeds us, and lights our homes.


There’s a scale to help you select the right light bulb, and  it’s called the “CCT” = CORRELATED COLOR TEMPERATURE.  The easiest way to remember this is that CCT is the COLOR of light in degrees “Kelvin”.  Kelvin is used to measure thermal, or heat energy.  For our purposes, the Kelvin scale runs from approximately 2,000 to 6,500 degrees. 



Think of it like this – if you have a piece of steel or a light bulb filament (technically known as a “black body”), it starts out black when you heat it.  As the temperature rises, that metal becomes red, then orange, then yellow, then white, and finally blue.  Degrees Kelvin chart that heat rise with light thrown off as a byproduct.  This is why old, incandescent bulbs are so inefficient - they're really heat sources, that oh, by the way, cast light, too.  


The CCT scale has a midway point at about 3,000 Kelvin, and that’s the difference between daylight (bright and bluer light) and warmer light – remember our toasty fireplace.  Different color temperatures have different applications, and yes – some make us look a whole-lot better than others. 


Cool colors up the Kelvin scale are unforgiving.  That’s why they’re sought-after in places like laboratories, warehouses and other industrial applications.  Winter-sky blues are reflected from most surfaces like skin, except for red.  Reds absorb that light and appear dark and muddy as a result.  This is why most of us look really bad in blue, ultraviolet light.  (Think of outdated department store dressing rooms.  Note to store owners – “If you want me to buy the expensive party frock, make me look good.”)


White light like bright daylight rings in at about 3,000 degrees Kelvin and can range as high as 5,500.  “Daylight” is usually a dominant option in store light-bulb aisles.  Bulbs at 3,000 Kelvin are great for offices and work spaces where folks need to be alert and able to see what they’re doing, and for use in home kitchens where we prepare food and hopefully don't chop off fingers.  And fish tanks can have CCTs that start at 10,000 Kelvin and go up.  


Some of the most beautifully lit scenes are rooms with fireplaces, candlelit dinners and cozy interiors with soft lighting.  The common denominator is yellow, and it’s the kindest light because it doesn’t contain much blue (remember, blue accentuates reds and makes them appear dark – like splotches and wrinkles.)


Warmer lights below 3,000 Kelvin are for homes, restaurants and even retail displays where how things look matters.  For that light, look for bulbs that either say “soft” or anything below 3,000 Kelvin.


One way to solve for a lot of this is to buy LED lamps that have adjustable color temperatures.  Technically, LEDs aren’t heated, thus producing light as a byproduct.  There’s another lighting scale called a “CRI” – color-rendering index – that shows how closely non-heat-generating lighting approximates those black-body light sources.  It’s an APPARENT color temperature.


LEDs can be tuned to mimic just about any color, and a number of these systems like the Phillips hue are available for $200 to $300. 


So remember – pick lighting for your application.  Warmer lighting (smaller Kelvin numbers) are more like inviting fireplaces and yummy interiors.  And higher temps up the Kelvin scale are cooler and more vivid.  


As always, reach out anytime with questions.  



IMAGES:  Edison light bulb from Amazon.com.  Light color chart from Westinghouse.com.  Fishtank from VangViet.com

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