Making Sense of Lightbulb Color

lightbulbs that illustrate a spectrum of Kelvin temperatures 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

bedroom lamp with incandescent lightbulbbedroom lamp with incandescent lightbulbIn 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 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.

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7 Responses to Making Sense of Lightbulb Color

  1. Anders Hoveland October 15, 2012 at 6:01 am #

    “Color temperature” will not really tell much about how the light is going to make the colors in your room look.

    The different type of light bulbs (regular incandescent, halogen, CFL, LED) all emit different spectrums of light. The light bulb manufacturers do like people knowing this because they prefer consumers to think that their CFLs can put out light just like incandescent bulbs or daylight. It’s just not true.

    Two different types of light with the same “color temperature” can still not put out the same color of light. And two light sources that do appear to be the exact same color of light against a white surface can still illuminate colored objects quite differently.

    I hate the light from CFLs. They are just not the same, despite what many people claim. They also give off UV radiation, and this can cause fading of your furniture over time. For the same reason, it may also not be a good idea to use CFLs as reading lamps or right next to your bed, where the bulb will be close to your face.

    Reveal bulbs have neodymium glass to filter out the yellow frequency light. All of the LED energy saving bulbs beiing sold now are deficient in both deep red and green-indigo frequency light. This means, for example, that if you have many red or teal colored objects in the room, LED may not be the best choice to bring out the colors, and your room will appear greyish and dull.

    I have been experimenting with combining halogen bulbs with bright white LED bulbs in the same room. I have found that this seems to make the colors the most vibrant. Just my personal preferences, but if I was remodelling my kitchen I would have about 40% of the light come from (3000K bright white) LEDs and 60% come from halogens.

    While I do not really like the light from LEDs themselves, in combination with halogen they can help push the spectrum more toards the bluer side. The halogens also have plenty of the deep red frequency light that the LEDs are lacking, so even adding just a little halogen light can significantly improve the color rendering. Incandescent/halogen light also has more cyan (green-blue) frequency light than blue, that can can really help even out the depression in cyan frequency light between the yellow-green and blue in LEDs.

    • EMC1402 August 13, 2013 at 1:09 am #

      Hi there! I know this post is fairly old but I stumbled across it and you seem to have a lot of info regarding lighting options. I just purchased a new home and painted the walls in the kitchen a creamy beige. I love the color in the daytime – a perfectly neutral beige. At night it’s peach, almost rose! They had 14 w 2700K Cfl Flood lights. So I did a bit of research and decided I needed to up the Kelvin to get less “warmth” out of the lights. I got 5000K and could have performed surgery on my counters! I went back for 3500K. The color is better but still slightly peach and the light is just not pleasing. I have previously liked the GE reveal lights but now I’m reading that these are 3500 K themselves. I just want soft, pleasing light and beige walls! Is it too much to ask?!

      • Jane F @ Atticmag August 30, 2013 at 3:22 pm #

        Thanks for stopping by and sorry for the delay in responding. We were on vacation.

        I haven’t seen the colors in your home but beige will always be a mutable color — meaning that it can color shift in different lighting. The changes result from the undertone in the paint (beige is a form of orange, hence the peach) together with the color quality of the light.

        5000K bulbs are bright white to blue and won’t be wonderful with beige I expect. Reveals have a red coating inside although they are around 2850K which can help some. You might also test LED bulbs which can have a cleaner, brighter light. I’ve had good luck with those.

        But ultimately with any muted color it may require trying out various different bulbs till you get the right effect at night.

  2. Jane F October 15, 2012 at 8:09 am #

    I agree with you Anders. Well and clearly stated! At the time I wrote this post, LEDs were not available. I completely gave up on CF and stayed with halogen. Currently, I have a workaround centered on LED bulbs and a long term goal for the lighting system in my house. I’m planning to post an update very soon.

    Thanks for stopping by.

  3. Santos Bayliss April 1, 2013 at 4:38 am #

    Incandescent bulbs are so called because of the heat produced. Incandescence means to glow with heat. The tungsten filament is found inside a void within the bulb. When energy is pumped through the wire, the electrons react and there is resistance. Then, the filament will get so hot it will glow.^


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