My search for a way to understand the color effects of incandescent vs compact fluorescent light.
We recently repainted the bedroom a wonderful yellow which looks sunny during the day and glows warmly at night. The room has overhead recessed lights for general illumination, plus a pair of bedside lamps with soft white incandescent bulbs. After one of the lamp bulbs blew out, my attempt to replace it pushed me to into the world of light bulb intelligence — a subject that’s far more complicated than it might appear.
Like many responsible home owners, I replaced a soft white incandescent 40 watt Sylvania with a 9-watt Westpointe 2700K soft white compact fluorescent. (Fluorescent bulbs produce more than three times the light of incandescents with the same input power).
The new bulb made the wall look lemony – a different color than the other side – and the ivory silk shade turned a little green. The change nagged at me.
The simple solution was to use the same bulb in both lamps so I turned to less eco-friendly incandescent 40-watt GE Reveal bulbs. Those made the walls pale terracotta rather than warm yellow, while the shades blushed a bit. Those Reveal bulbs were long marketed as bright white, but GE did not provide their color temperature on the label. I later learned through a colleague that Reveal lamps have a color temperature of approximately 2850 degrees Kelvin.
Color temperature – expressed as Kelvin or K – measures the color spectrum of light, akin to heat measurements expressed as Fahrenheit and Celsius. Every light source has a color temperature and manufacturers put the K temperature on most light bulb packages to help you determine whether you’re buying warm (lower numbers) or cool (higher numbers) bulbs.
The easiest way to understand the differences in color temperature is by looking at a photo I took [top] at a lighting expo. The apparent color temperature of these of Nippo fluorescent bulbs shows the warm to cool light progression at a glance. I enhanced the labeling for easy reference.
Some handy approximations support the photo:
Candlelight and firelight = approx. 1800 K
Typical household incandescent bulbs = approx. 2700-3600K
Daylight/sunlight = approx. 5600 K
Sunlight at Noon = approx. 6700K
In general, lower the Kelvin temp, the warmer (more yellow) the light; the higher the Kelvin temp, the cooler (bluer) the light.
Also, light with a higher color temperature (more blue) appears brighter and produces higher contrast which makes it preferable for working and tasks.
The clinker: Manufacturers determine the temperature of their bulbs with no standards for the descriptions apart from Kelvin measurements. Also, incandescent and fluorescent bulbs have slightly different color spectra (fluorescent has more green) so even at the same color temperature the appearance of color can be very different for each bulb.
Some specialized websites (generally those selling bulbs) will give approximate color correspondence from incandescent to compact fluorescents but trial and error are required for success.
Light bulb packages also are emblazoned with a variety of other terms, including:
Watt – Measure of electrical power (w)
Volt – Measure of electrical charge (v)
Kelvin – Measure of color temperature (K)
Lumen – Measure of light brightness (lu)
Candela – Measure of light intensity (cd)
Ampere – Measure of electrical current
Light Bulb + Paint Strategies
Because light influences the color of the objects being viewed under it, changing a light bulb changes color in a room. That helps explain many paint disaster stories as well as the effects I noticed in my mutable yellow bedroom. (According to a photographer on photo.net who took a measurement with his color temperature meter, Reveal bulbs are about 3400-3500K. Those gave the walls a pinker cast than the 2800K compact fluorescent bulb which appeared more green.)
It will be essential to understand color temperature if 100-watt incandescent light bulbs are no longer sold, beginning in January 2012. By January 2014 (as mandated by the Energy Independence and Security Act of 2007) 40 watt incandescent bulbs may be gone.
So I haved juggled and experimented with compact fluorescents of various temperatures to see how their light interacts with my paint and furniture colors. Currently, I have Westpointe “soft white” (2700K) and natural light (4100K) plus GE daylight bulbs (6500K) to compare against incandescent GE Reveals and a few traditional “soft white” Sylvanias.
Unfortunately, my paint colors are mostly muted making it different to capture the various qualities of light in photos of a yellow bedroom, a pale blue living room, celery-green sun room, and silver-gray study.
Over the next five years, I expect new lighting technology to fill the gap left as incandescent bulbs exit and compact fluorescent color is tweaked. Maybe.