Post 712 -by Gautam Shah
Brightness and Colour have mutual dependence. Greater brightness leads to sharper visual perception and the colour (spectrum) affects the perceived level of brightness. Physiological and environmental conditions alter the perception of brightness as well as colours. Noon time daylight conditions are accepted as the optimal brightness condition for experiencing the colour. But this condition of high brightness can reduce the contrast between two near by objects and so confuse the colour perception.
Brightness and colour, both are strongly affected by the immediate past experience. Sudden transition from darkness to brightness or one colour to another affects the pupil dilation.
Brightness and colour relate to reflection from a surface. The quality of a surface, the texture and its grain orientation vis a vis the directions of illumination and observation, affect the perception. Most of the objects reveal their multiple surfaces concurrently but brightness and colour on each of the face seems different. In this scenario the source of illumination (if solar) and observers both vary their position. As a result colour perception is very dynamic phenomenon. In Architecture or Interior design colour matching or determination of brightness is always worrisome affair.
Next factor is the context in which objects or scenes are observed. The juxtaposition with a lighter background enhances and darker backdrop setting dulls the perception of brightness and colour.
Colour perception operates at three basic levels, as the capacity of a surface to reflect light, as emission of light from a hot body and the personal capacity to differentiate various colourations. But the conveyance of the ‘colour related experiences’ is even more difficult. The interpretation of colours varies in different setting of locations, cultures and circumstances. Environment and Terrain are two major factors that alter the colour. Environmental conditions like solar brightness, inclination, orientation, cloud-cast conditions, atmospheric refractions, etc. vary depending on the geographic location. These are further attuned by the surface extent, texture, angle and duration of exposure. The terrain offers very pervasive colour context against which everything is observed. The different terrain effects are really not perceived on the site, but experienced through time-space segmented documents like photographs, paintings, videos or movies.
The conditions at ground level such as surface colour, wetness, snow, vegetation cover, topography, orientation, man-made and natural features, surroundings, density, reflection (albedo), absorption, altitudes etc. determine the colour quality of light. Since all these surface conditions are very localized, the colour variations are conditioned by them. The buildings in surrounding areas, immediate terrain and water bodies have a bearing on the quality of illumination entering a building.
Illumination in a space is Natural (daylight, chiefly solar origin), Artificial and often combination of both. Daylight has Four important facets, the illuminance, warmth, colour and the variability. Daylight on an outdoor location is a combination of direct sunlight, diffuse sky radiation, and both of these as reflected from the earth and other objects. The brightness and colour of daylight are governed by the sky conditions, like clouds, fog, smoke, atmospheric pollution, morning and evening twilight zones (when the atmospheric scattering of predawn sunlight takes place).
The solar radiation as received on the surface of Earth varies from place to place, season to season, day to day and even hour to hour. Equatorial regions receive more radiation, than polar regions. Darker surfaces, like the tropical forests reflect very little radiation, 10 %, compared to snow bound high latitude areas, which nearly reflect 80 % of the energy received. Cloudy and dust polluted areas receive less solar energy. Direct sunlight at noon can have illuminance as high as 120,000 lux (Compared to this moon light is <1 lux). Sunlight is a warm colour light, at noon, the colour-temperatures are about 5500°k, bluish-white or ‘cool colours’ and at sunset, these are about 2700-3000°k (degrees kelvin), are yellowish-white through red or called ‘warm colours’.
The reflected light from the exterior surfaces of buildings, roads and pavements affect the illumination on lower floors of the buildings. These cause minor variations due to movements of people, vehicles, ripples on water bodies and leaves of trees. Upper floors of tall buildings, except in similar localities, receive fairly consistent, but very strong daylight from nominal windows. Such floors with low or no sill windows (glass curtain walls) get varying levels of illumination, often strongly coloured.
Reflectance of rooms’ interior surfaces impacts the perception of brightness and colours in a space. The surface reflectance is a function of colour, its texture (matt, dull-sheen, glossy) and the orientation of grains of textures. Extreme levels of brightness, if, are present within the same field of view, can be calibrated by the surface texture and colour. Historic buildings, sites and remains, are conserved with surroundings updated through paved stones of same colour-texture as the original built-form or green lawns. These choices, alter the degree of interior brightness, as well the quality of colour.
Similarly cities conserved with enforced thematic colours (blue -Jodhpur, Pink -Jaipur, both in India, white -Santorini, sienna browns -Italian, Piazza del Campo and ), create monotonous colour tonality in interior spaces.
For artificial illumination sources Brightness and Colour have some sensorial connection. Artificial light sources one commonly accepted rating, the Colour rendering index (CRI). It is supposed to index ‘how the colour will look’. High CRI (nearly equal to daylight in afternoon) will mean colour will look ‘real and right’ and low CRI will mean unreal (weird) and wrong. CRI has limited relevance, if only the illumination source is white (Candles and incandescent bulbs can have high CRI ,but are off-white. The sodium lamps have low CRI but high brightness.