Technical Explanation: The CRI is a unit that measures the ability of a light source to reproduce the colors of objects faithfully in comparison with an ideal source of light, or natural sources such as sunlight. The CRI is a determined value from 0 to 100, with 100 being the value “perfect” or daylight.
Real World Explanation: The CRI determines how you and your surroundings appear to you and the other people in your environment.
It is crucial for a lighting designer to know how humans react to different colors of light and to the contrast between light and dark. This knowledge combined with knowing what tasks are performed enable the designer to effectively illuminate an interior space.
The eye functions almost like a camera sending images to the brain. Cones in the eye provide color vision in bright environments and rods in the eye provide shades of gray in dark environments. Brightness defines luminance which is the intensity of light entering the eye. Light meters measure this as lumens. The variations in the brightness of objects is defined as contrast. Colors in the middle of the visible spectrum appear brighter than colors at outside edges of the spectrum.
People react differently to different colors and have likes and dislikes for colors. Light and color influence our mood and feeling and affect our biorhythm and circadian rhythm. Red light is psychologically stimulating and can even raise blood pressure and heart rates. Red objects appear closer that they actually are. Blue is the opposite of red. It has a calming effect and appears further away that it is. Green is the most restful color for human vision.
In addition to color the amount of contrast determines how one perceives an architectural space. Environments that are complex, asymmetrical, unfamiliar or unorganized cause a sensory overload. In such situations complex tasks are avoided because people are distracted, annoyed or frustrated. Therefore attention to color, contrast and the activities that occur will enable a lighting designer to match the lighting to the tasks and create an inviting space.
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