Colour

The perception of colour is often a primary consideration for glazing selection. Objects we can see, whether they are transparent, translucent or opaque, all have a specific colour.

Glazing colour depends on parameters such as illumination type, reflection and transmission properties, observer eye sensitivity and the environment surrounding the building. Therefore, it is highly variable based on the time of day and level of natural light.

Clear glazing has a slightly green transmission colour, while the optical qualities of coloured glazing vary widely depending on their thickness. Bronze, grey, blue and green float glazing reduces the amount of solar energy and the level of light transmission. As such, the view through glazing is influenced by the colour of the glazing itself.

There are various ways to discuss glazing colour, which can be brought to good use when comparing products for likeness or specification.

Colour Rendering Index

The Colour Rendering Index (CRI) is a useful metric that quantifies the ability of transmitted daylight through the glazing to portray various colours compared to those seen under daylight without the glazing.

Based on a scale of 1 – 100, a low CRI causes colours to appear washed out, while a high CRI causes colours to appear vibrant and natural. In commercial glazing, CRI indicates the effect the specific glazing configuration has on the appearance of objects viewed through the glazing.

CIE Lab Colour Model

The CIE Lab Colour Model is another way to interpret glazing colour that quantifies the difference in transmitted or reflected glazing colour.

A colour model is an abstract mathematical model describing the way colours can be represented as groups of numbers. The generally accepted measurement for colour in glazing is the Commission Internationale d’Eclairage (CIE) L*a*b* system, which splits the colour into three scales: L*, a*, and b*. L*, a*, and b* are often available from glazing suppliers and can be converted to compare the difference between glazing colours numerically or converted into RGB or CMYK for rendering.

Care must be taken when viewing colours on monitors or in print since most printers and software utilise an RGB or CMYK scale; therefore, the output depends on the device or material type.

Exterior Solar Absorptance

When we refer to the solar absorptance of a wall or roof, we reference the proportion of total incident solar radiation absorbed by the external material. That which is not absorbed is reflected.

A surface with a low solar absorptance will reflect more heat than a roof with a higher solar absorptance, keeping the roof space and interior cooler on a hot day. As roofs are more often perpendicular to the sun, their colour is more important than walls when considering the potential for improved energy efficiency or comfort during the day.

Typically, solar absorptance is related to the colour ranges shown below. Where the actual solar absorptance is unknown, light, medium or dark can be used to identify the approximate solar absorptance value. However, the actual tested values are typically available from suppliers.

Solar Absorptance	Typical Colour
< 0.475	Light
0.475 - 0.7	Medium
> 0.7	Dark

Light Reflectance Value (LRV)

Understanding internal light reflectance is critical when designing good, balanced daylighting. A component of this strategy is the colour of the interior surfaces. Typically, this internal reflectance of colour is determined via the Light Reflectance Value (LRV).

We use LRV to understand how bright or dark the finish within an interior space may appear. By selecting a more reflective paint, we may be able to reduce the required number of light fixtures and improve the overall uniformity of light.

From a technical standpoint, an LRV determines the quantity of visible and usable light reflected by all directions and wavelengths to identify how much light a colour reflects or absorbs. Measured from 0% (no visible light reflected) to 100% (all light reflected), the darkest blacks have an LRV rating of 5%, while the whitest whites average around 85%.