For a user of lights, it is confusing what color temperature they should specify for their office environment. I will try to shed some light on the psychology and the technology as well as make some recommendations to aid the decision as to what color temperature to choose for an office environment.
I try to be fair and informative and the presentations are based on facts of technology and physics of the current art.
What is the Correlated Color Temperature (CCT)
A CCT value is a simple way to communicate chromaticity, the color appearance of “white” light emitted from electric light sources.
Values for CCT for most commercially available light sources range from 2700 K to 6500 K. CCT values are intended by the lighting industry to give a specifier a general indication of the apparent “warmth” or “coolness” of the light emitted by the source.
By convention, lamps with low CCT values (2700 K to 3000 K) provide the light that appears “warm,” while lamps having high CCT values (4000 K to 6500 K) provide the light that appears “cool.” This convention may have been established because non-electric light sources with low CCTs, such as fire or a candle the mind will associate with warmth.
To address the potential problem of lamps with the same CCT having a different color appearance, the lighting industry utilizes a color tolerance system in conjunction with CCT to specify color consistency.
For an office environment where people are not expected to sleep or feel too relaxed, a cool color temperature will provide more alertness and higher contrast for reading as well as for camera systems.
There is little difference between 4000K and 5000K in appearance but 5000K phosphors are generally more efficient and provide a better use of energy compared to 4000K phosphors.
There is one exception when you are evaluating color graphics in the office, you should use the color temperature of the location where the art will be displayed; outdoors 5000K or make sure you get real daylight.
If you are evaluating in-store graphics you will have to provide an area where you re-create the lighting CCT and CRI of the target location to get a real or close perception.
I strongly recommend against CCTs above 5500 K, they do get very selective in their spectrum and some people get annoyed by too much blue. I certainly do and even get nauseous on pure LED blue.
What is the Color Rendering Index (CRI)
For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT).
It is the general consensus that CRI is not a good indicator for use in visual assessment, especially for sources below 5000 Kelvin (K). My guidance for an LED light is to not be below a certified CRI of 68 and most white LEDs will be around 70 or better, better gets more expensive due to the more refined phosphors but it will not give you any better color recognition in an office environment.
There is one exception when you are evaluating color graphics in the office, CRI will matter to a degree and my suggestion is a minimum CRI of 80 as you will not see much difference between a CRI of 80 and a CRI of 100.
Facts of Fluorescent Tubes and CFL lighting
When fluorescent tubes and CFL lamps are advertised at a particular color temperature then this means when they are a few hours old. The test for a particular color temperature does not reflect the actual color temperature after a few months or years of operation. What that means, and all of you have seen this, color temperature of any fluorescent tube changes with age so does its light output or brightness.
By that fact when fluorescent tubes get old they produce a brownish sometimes greenish light and if people have been in such an environment for a long time will accept this as the norm.
As people do not like change very much they often are looking for a light that has a lower color temperature in LED to emulate a really old fluorescent tube.
The color rendering of a fluorescent tube of CFL also shifts significantly with age and use and the spectrum of this type of device is not very consistent, hence color reproduction of documents is poor and inconsistent.
When we started to develop LED fixtures for use in office spaces and their efficiencies were just reaching those of fluorescent tubes but only with a CCT of 5500 K or higher our offices were still lit with old fluorescent tubes.
The male population was overwhelmingly happy with the more daylight appearance of light. The female part of the office initially preferred a less cool light.
Today, both male and female would not want to go back to the old lighting.
Also today, any color temperature of 2700, 3000, 3500, 4000 and 5000K is way better than the efficiency of fluorescents tubes, so there is no longer a case for the industry of LED lighting to argue for the higher temperature for efficiency sake.
There is a NASA study that suggests that warmer light sends the body a message to slow down at the end of the day and cooler light as is the case in the morning signals the body to be alert and start the day. If that theory holds for safety and performance reasons one would want 4000K to 5000 K in the office and have the better use of energy at 5000 K as a bonus.
A Word of Caution
True 5000 K LEDs from a good manufacturer are not blue. However, 6000 K to 6800 K LEDs marketed and sold as 5000K are blue but you get what you pay for.
Cheaper LED lights generally do not guarantee a CCT and will advertise say 5000 K with a caveat that the CCT may be between 4500K and 6000K – lookout for that as it will look awful in an office space if the color temperature between different fixtures in one view is different.
Good manufacturers will control the CCT and stay within ANSI Standards so that the appearance of all fixtures in an area is the same.