There is no such thing as the absolute "tube" colour of any material: the perceived colour is a function of the light it is viewed under. However, we can make a general statement: the higher the Colour Rendering Index (CRI) of a light source (also denoted by Ra) the better - and more natural- colours appear under the light source.

The ability of any given light source to represent colours in objects is its Colour Rendering Index or CRI. It is based on a relative measurement which will rate light sources on a scale of 0 to 100. The higher the CRI, the more natural the colours appear. Lamps with very good (70-80 CRI) and excellent (80+ CRI) colour rendering properties are accepted as "high quality light" because objects and people will look more appealing and natural. As well, the light level itself will be perceived to be higher.

In measuring CRI, eight specific colours are compared against two reference sources: incandescent lighting is the reference for warm colour lamps and natural daylight for cool colour lamps. Both incandescent lamps and natural daylight are considered to have CRI's of 100 even though, as we know, materials appear quite different when viewed under these two lights. These light sources are very different in colour temperature although both have perfect CRI's.

CRI is considered a useful measurement especially in settings where it is important for people or objects to appear as natural as possible. Examples include retail shops, restaurants, offices, hospitals, health clubs, paint shops, and print shops where high colour rendering can reproduce natural hues and augment visual clarity.

CRI Comparisons

CRI Range Applications	Rating	Typical
80+	Excellent	Retails (displays, stores and shops) Showrooms Restaurants Executive offices Conference rooms Lobbies
60-80	Good	Offices Classrooms Security lighting Supermarkets Manufacturing areas High bay retail Large scale exteriors (sports areas)
< 60	Poor	Street lighting Warehouses Parking lots