What Is Meant by “Color Temperature” in Reference to Fluorescent Light Bulbs?

Some of the most common questions we receive concerning fluorescent lighting involve color temperature. The purpose of this post is to clear up some of the confusion.

Color Temperature refers to the color of light produced by a fluorescent light bulb. Color temperature is measured in degrees Kelvin and generally range from around 2700K to 6500K. What is important to remember is that the lower the number the warmer (more yellow) the light will appear. Conversely, the higher the number the cooler (more white or even blue) the color will appear. Fluorescent color temperature is controlled, or determined, by the composition of the phosphors lining the glass of fluorescent tubes. Often times, especially in retail packaging, color temperatures are not given in degrees Kelvin, but instead are identified by the terms Warm White (3000K), Cool White (4100K), and Daylight (6500K).

Often the question is posed to us: “What is the best color temperature for me to use?” The answer to this questions depends on two factors—personal preference and application.

Most often, personal preference determines what color temperature light bulb one should choose. When switching from standard incandescent or halogen light bulbs to compact fluorescent, people often want to match the color of their existing light bulbs. To match standard incandescents one should choose fluorescents that are 2700K. To match halogen lighting one should choose fluorescents that are 3100K.

Resistance to the use of fluorescents is often a result of consumer’s distaste for the color of light they typically associate with fluorescent lighting. In the past, fluorescents were almost always seen in institutional settings such as schools, hospitals, and offices. In these settings, Cool White (4100K) bulbs have been used almost exclusively. While providing crisp white light, this color temperature provides an almost antiseptic appearance that is typically not desired in the home. We often hear consumers state that they don’t use fluorescent light bulbs because they do not like how fluorescent light looks. These consumers tend to be unaware that fluorescent lights can produce a wide range of colors and that some are virtually indistinguishable from other light sources such as incandescent. Again, often times it’s simply a matter of personal preference.

The second factor in choosing a color temperature is the application under which the light bulbs will be used. As stated above, for general ambient household lighting warm colors are generally most appropriate. Now consider a retail application in which products are sold for use in homes, such as furniture or carpeting. The retailer would be wise to use warm lighting that matches what is used in typical homes. After all, when choosing a product the consumer wants to know what their couch or rug will look like when they take it home, so lighting should remain consistent.

Another retail application involves actually masking the true appearance of a product—your local grocery store’s meat case. Grocery stores will often use warmer color fluorescents (around 3000K) in their meat cases while using a cooler color light bulb (4100K) throughout the rest of the store. The warm color accentuates the red color of the meat while masking, our washing out, brown and grey colors (this also involves the concept of Color Rendering, which we will address in a later post). Next time you go shopping try watching the brown and grey spots on your steak magically appear and disappear as you move it back and forth from under the meat case’s lights to the general store lighting.

You may have noticed that some fluorescent bulbs produce a pure white light. This light is generally around 5000K. This color of light is ideal for tasks that require high levels of visual acuity such as reading, sewing, modeling and crafting, or any activity involving tiny parts. In explaining why 5000K light is ideal for these applications I will introduce the concept of Scotopic Lumens. Scotopic lumens refer to the amount of light registered by the rods of the human eye (which also controls pupil size). 5000K lights are high in scotopic lumens, thus small objects are easier to see. You will notice that high quality lamps designed for reading and sewing, such as our Verilux and OTT light fixtures, utilize 5000K-5600K fluorescent light bulbs.

In summary, when choosing the appropriate color temperature you should consider both where you are using the light bulb and what you will be doing under the light it produces.