CCT & CRI in lighting design of spaces

Color is not a inert characteristic of any object

contd.

instead it comes with the perception of observer influenced by type of light falling

CCT and CRI are extensively used color metrics in lighting industry to explain color appearance.

Definitions of CCT

Correlated Color Temperature CCT is a measure of how warm or cool a light source appears to the human eye. It is measured in degrees Kelvin.

According to Wikipedia correlated color temperature of specific light source is the temperature of an ideal black body radiator, which radiates light of comparable hue to that of light source.

Why CCT is considered in light designing of spaces?

CCT values are needed for selection of

luminaries for lighting design of

spaces. They are intended by the

lighting industry to give specifiers a

general indication of the apparent

"warmth" or "coolness" of the light

emitted by the source.

contd.

Especially it is a prime tool for creating

themes and atmosphere for a space according

to requirement. For example, a warmer (i.e.,

lower color temperature) light is often used in

public areas to promote relaxation, while a

cooler (higher color temperature) light is used

to enhance concentration in offices (2008).

Limitation

In practice, CCT rating should be limited to white light source (not sodium sources for example) (ASSIST, 2010). Color temperature is only meaningful for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e. it does not make sense to speak of the color temperature of e.g. a green or a purple light (Wikipedia.com).

contd.

One of the potential problems of CCT is

higher color temperature yield cooler

colors of light which is subject to

confusion as opposite of the cultural

associations attributed to colors , in

which "red" is "hot", and "blue" is

"cold".

CRI

Definitions of CRI

The color rendering index CRI

according to McCamy(1992) a

quantitative measure of the ability of a

light source to reproduce the colors of

various objects faithfully in comparison

with an ideal or natural light source.

contd.

While Light Research Centre describes

color rendering index as a measure of a

light source's ability to show object

colors "realistically" or "naturally"

compared to a familiar reference

source, either incandescent light or

daylight.

CRI value

CRI values range from zero to 100. In

actual rating above 80 of a light

source is considered good for interior

setting especially retail merchandizing.

While below 70 is not good CRI

especially for retail setup.

Poor CRI Good CRI

CRI of Lamp Sources

Why CRI is considered in light designing of spaces?

CRI is needed by the architects and

interior designers for considering in

optimum selection of luminaries for

lighting design of spaces. As different

areas have different consideration

regarding color and light appearance.