Light bulb color is measured in two ways. The color of the light as you look at is measured by temperature in units of the Kelvin temperature scale. Equally important is the total spectrum of color the light bulb emits. This is represented using the Color Rendering Index, with 100 being the best rating. It used to be that typical office fluorescent lamps were “cool white” with fairly low CRI ratings. As of 2010, the trend is toward full-spectrum lighting that simulates natural daylight.
Color Temperature References
Light color falls along a continuous spectrum and is represented by a color temperature measurement unit called the Kelvin (K). It may seem backward, but the higher the K the cooler or bluer the light source. Some helpful references are: candlelight-1,000 K; early sunrise-2,000 K; incandescent bulbs-2,700 K; noon daylight-5,000 K; color-balanced computer monitors-6,500 K; overcast daylight-7,000 K; and north light-10,000 K.
Color Temperatures of Fluorescent Bulbs
Fluorescent bulbs, both overhead tubes and compacts, are sold in color temperatures with names similar to these: warm white-2,700 K; neutral white-3,000 to 3,500 K; cool white-4,100 K; and daylight-5,000 to 6,500. Numerous studies on seasonal mood disorders and increased worker productivity under more natural daylight lighting has prompted many companies to switch to full-spectrum bulbs with a higher color temperature.
Color Rendering Index
The color temperature of a light bulb is only one measurement of its color. The Color Rendering Index (CRI) is a measurement of how natural objects viewed under the light will look based on how completely the bulb emits a full color spectrum of light. A score of 100 is considered the best rating. Most inexpensive fluorescent bulbs of any color temperature tend to have CRI ratings of only about 55, which is why people turn out looking a strange color when you photograph them without adjusting the color balance. However, full-spectrum fluorescent bulbs with CRI ratings of more than 95, which were once so expensive they were used only by graphic arts and other industries needing to match color carefully--are now available at a price that makes them feasible for office overhead lighting.
Cost Consideration in Choosing Fluorescent Bulbs
There is no question that the front end cost of full-spectrum daylight fluorescent bulbs is higher than conventional replacements used by most companies. Mixing the color temperatures of cool white and daylight bulbs looks strange, so making the switch usually requires a commitment to replacing all the bulbs, which can amount to a substantial investment. However, full-spectrum fluorescent bulbs are manufactured to more exacting standards and have longer life spans, so they do not need to be replaced as often. In addition to obvious cost savings this also reduces labor needed to replace bulbs and hazardous waste management and disposal costs to get rid of them because of their mercury content.
LED Replacements for Fluorescent Bulbs
Although still expensive, LED arrays, with promised life expectancies of up to 10 years, have appeared on the market as replacements for both fluorescent tubes and compacts. They come in different power outputs and a variety of color temperatures with full spectrum capabilities. One type works without the ballast units needed for conventional fluorescent fixtures, and the other can simply be inserted into existing fixtures without rewiring as bulbs need to be replaced.