What Kind of Color Temperature to Use in an Office

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 at 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 light that appears "warm," while lamps having high CCT values (4000 K to 6500 K) provide 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.

Anecdotal

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 - look out 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.

Klaus Bollmann is a 30 year veteran in energy conservation, resource saving innovative products for a sustainable environment. Click the link If you are interested in ActiveLED high performance lighting and LightSpace energy saving control products.

The Aston Martin DB4 GT Zagato Sanction Sports Car

Aston Martin DB4 GT Zagato Sanction - A close look at this sports car including performance, technical data, features, comparing rivals, history, used prices

from Classic to Modern

Aston Martin DB4 Zagato on the Track

Four of the chassis used on the original Zagato sports car (also referred to as Sanction 1) were duly modified to produce lightweight versions that would be ideal for racing.

These racers incorporated the following features to improve aerodynamics: A lower roofline - Enlarged rear wings, with a restyled tail section, and an extended front section.

One of these restyled Zagatos made it debut at the Goodwood race track in early 1961 when, driven by Stirling Moss, it finished in third position, with its arch rival, the Ferrari 250 GT, taking the chequered flag.

However, a couple of months later, two of the quartet, supported by Aston Martin and assigned to Essex Racing, were entered in the Le Mans 24 Hour race, but both were forced to retire.

Not to be outdone, in July 1961, one of these cars claimed the Zagatos first win in one of the races as part of the British Grand Prix.

A further attempt at Le Mans in 1962 ended in early retirement through engine failure.

Aston Martin DB4 Zagato Sanction 2

Production of the DB4 Zagato ended in 1963 with 19 of the sports cars being built.

However, this was not the end of the story. In 1988, having approached Aston Martin, it was decided to modify four of the original DB4 chassis so that they could be transformed into a lighter weight construction, identical to that used in the DB4 GT.

These were then shipped to Milan to receive bodies comparable to those used in the original Zagatos of the early 1960's, with the distinctive small oval grille, and a smoother, restyled rear section.

The first of these modified rolling chassis was shipped in January 1989, with the fourth three months later.

These four officially approved replicas were designated as Sanction 2 cars.

Although there was little difference, externally, from the originals, modifications were made to improve the handling characteristics, whilst the engine capacity was increased from 3.7 to 4.2 litres, and the size of the road wheels was reduced from 16 to 15 inches.

All four replicas were completed in July 1991, but were not permitted to display the original Zagato badges.

When placed at auction, these replicas were sold for as much as $1.25 million.

Aston Martin DB4 Zagato Sanction 3

Following the sale of the four Sanction 2 Zagatos, it was found that there were still two additional Zagato body shells that had not been used, for whatever reason.

Therefore, in 1992, Aston Martin was approached with a view to creating further Sanction variants.

Following agreement, another two DB4 chassis were discovered, and were duly modified to produce, in conjunction with the newly found Zagato body shells, a final two DB4 Zagato replicas, which were completed in 2000, sporting the original Zagato badges.

These were designated as Sanction 3 sports cars.

Other Replica DB4 Zagatos

By 2000, a total of 19 original and 6 Sanction DB4 Zagatos had been built, and were highly prized, with six figure valuations.

Accordingly, since then, other non-original, and non Sanction replicas have been built, based on the chassis from DB4's and DB4 GT's.

However, such replicas did not have the Zagato sports car cache but were, nonetheless, still desirable, and with a ready market.

This concludes my Aston Martin DB4 GT Zagato Sanction Sports Car Review

To view my ORIGINAL more detailed article, containing Photographs, Videos, Technical Data, and Charts not shown above, then please click the following link: