Light is the most important material.

Architects spend hours selecting wall colours, floor finishes, upholstery fabrics. Then light is often addressed at the end. With the result that the carefully chosen materials lose their effect under the wrong light.

Colour temperature.

The colour temperature of a light is measured in Kelvin. Low values, from 2200K, are warm and yellowish. Like an old-style incandescent bulb. Higher values, from 4000K, are neutral. Very high values, from 6000K, are cool and bluish.

Warm lights make warm materials glow. Wood looks lively. Natural stone in beige tones looks natural. But cool materials appear dull. Grey concrete looks tired, bluish fabrics lose their clarity.

Cool lights are the opposite. They bring out cool materials but make warm colours look pale.

In living spaces 2700K to 3000K is common. In workspaces 3500K to 4000K. In galleries and for material assessment 5000K to 6500K, because a neutral perception is desired there.

Colour rendering.

The colour rendering of a light is described by the CRI value, from 0 to 100. Daylight has a CRI of 100. It shows all colours as they are.

Artificial light falls below this. A budget LED has a CRI of 80, which is acceptable for living spaces. A high-quality LED reaches 90 or more, which is necessary for spaces where materials need to be shown. Galleries, showrooms and clothing stores work with CRI 95 or higher.

With a low CRI, materials lose their depth. Red woods look brown. Green fabrics look greyish. Marble looks plastic. Those who specify materials without knowing the CRI of the light risk disappointment with the client.

Light direction.

How light falls on a surface determines how the surface reads. Raking light, arriving almost parallel to the surface, emphasises every texture. Natural stone appears more three-dimensional with raking light. Wood grain becomes visible. Plaster shows its texture.

Direct frontal light does the opposite. It flattens. A rough wall looks smooth. A natural grain disappears. Those who choose materials for their haptic quality should plan the light so that this quality remains visible.

How we document it in the library.

In the Material Concierge libraries we record for every sample how it looks under standardised light. That is not the whole story, but a start. Those comparing materials should assess them under the light that will be used in the finished room. Otherwise the result will not match at the end.