Lighting Reflectance Explained

Understanding Reflected Light in Interiors

It is important to remind ourselves that ‘lighting’ is not all about artificial light. In earlier posts we have also discussed daylight and reflected mirrored illumination within an interior. All these factors must be accounted for, if the subtle balance of lighting is to be achieved. Indeed, the illuminance emanating from all surfaces in a space must be considered.

Definition of Luminance

To be exact, luminance is a measure of how much light is emitted from a surface in a given direction.

So the level governs not only how the colour of a wall, ceiling or table top appears to the eye but also how much light the surface reflects back into the room. The rates of luminance across a colour pallet may surprise you – certainly give you something to reflect on…(apologies!)

Luminance Lighting Theory

The amount and nature of the light reflected from a surface depends on whole raft of factors. As a designer, you will have intuition to gauge how much light to provide. Naturally we know instinctively that dark coloured rooms need more light. How light actually behaves according to the colour and nature of the surface is important to know across the whole palate of available colour especially when selecting your lighting and it’s positioning.

3 Basic Types of Surface Reflection To Consider

Analyse to what extent they are present in your interior and how this will influence the space.

Specular Surfaces

  • Specular Surface– mirror / highly polished metal surface – reflecting equal amounts of light at equal angles. These are very smooth surfaces.

Diffuse Surfaces

  • Diffuse Surface– matt emulsion paint will highly diffuse light sending it back widely giving the impression that it is equally bright in all directions. These are rough surfaces.

Satin & Glossy Surfaces

  • Satin and glossy surfaces– a combination of specular and diffuse reflection depending on how shiny the surface is. These are smoother surfaces that respond similarly to the diffused category.

Colour & Reflectance Values

Light reflected by a coloured surface will be tinged or tainted with that colour, but it’s rarely an issue to concern yourself with – unless designing a scheme for a colour sensitive interior where colour representation is important i.e. a clothing store.

The colour of the surface will have a reflectance value. All coloured surfaces absorb some of the light that falls upon it, therefore creating a scale of reflectance determined by how much light is bounced back. Worth noting is the Table of Light Reflectance Values. Using a set of coded swatches to match as near as possible with the surface colour in question, a pre-measured percentage of reflectance can be referred to and then used in calculations to gain a better understanding of how the space and surface will be lit.

This interior above shows the entrance to some very nice toilets within the restaurant at London’s Skygarden and demonstrates this principle. Some light from the downlight in the ceiling is reflecting off the timber clad back wall. Approximately 50% of the light reaching the wall will be reflected back into the space. The light which reaches the floor is reflecting off a light coloured shiny tile, therefore reflecting a higher amount of approximately 80% of the light back into the space.

Colour Perception

Another factor to consider is all colours of light have a wavelength value with certain colours processed more efficiently by the human eye than others. For example using the same amount of light a green is very strong whereas a red is relatively weaker in appearance.

Visual Adaption of Colour

Our eyes and brains operate an amazing automatic process; a natural visual system called Adaption. As designers, we need to be aware of this process to deliberately tune the intended visual response to our environment. When exposed to a particular colour for a period of time, the brain will normalise the response to the colour, akin to a visual reset or a white balance on a camera. For example when working in a cool white 4000K or daylight 6500K room, walking directly into a 2700K room will feel like you are entering into a disconcerting world of orange light! The eye needs a little time to compensate and re-adjust its bias. If we remain mindful of this natural process as designers, we can assist this correction by creating transition areas of intermediary light.

As designers we also need to gain some understanding on how a surface will look according to the angle of light that plays upon it. A rough and textured surface will be accentuated when lit with directional oblique light. Even a flat surface when lit obliquely can appear horrendously flawed as every bump is highlighted.

Variations of Surface Reflecting Light

Conclusion to Understanding Reflected Light

Reflected Light Reference Guide:

Simply remember these 3 key questions when considering reflected light in your space.

Colour of surface = How bright it will look and the amount of light it will contribute back into the space

Type of surface = how the light will bounce back – equally as given or very diffused or a combination

Amount and type of light = the output and colour temperature of the light

Reflected Light Bathroom Case Study

As a second part to this explanation, learn how this Luminance theory was essential to understanding a real problem a client had with the lighting in a bathroom we had designed together and how the choice of tiles were not looking as they expected. Bathroom Tile case study is in another article within this website found here

There is wealth of knowledge available at Orange Lighting and offered free to our designers and architects searching for the ideal effect and the right light fitting to create that desired look. Just call!

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