Light Source

The surface color of an object is affected by the nature of incident light.^39,45 Metamerism is a phenomenon that may cause two objects to appear to match under one light source, however, they may be perceived as unmatched when the lighting conditions are altered (attributed to different spectral reflectance) (Fig. 15);^4,7 This phenomenon is associated with restorations appearing to blend with natural teeth under the operatory light but looking different when the lighting conditions are changed. Thus, it is advisable to perform shade selection under different light sources to avoid the effects of metamerism.^4,28

Fig. 15 - Both the objects appear to match when illuminated with light source “A” but appear unmatched under light source “B”

Fig. 15 - Both the objects appear to match when illuminated with light source “A” but appear unmatched under light source “B”

Types of artificial light sources

Various light sources emit different colors of light.³⁹ Ceiling lighting in a dental office is dull and not sufficiently bright whereas the dental unit lights are too bright and result in a glare.⁴ An increase in light intensity and glare decreases the accuracy of shade selection.⁴ The common types of artificial light sources present in the dental operatory include the following:

• Incandescent lights: These light sources emit a high concentration of yellow waves.^4,28 They make bright colors such as red, yellow, and orange appear more intense, whereas cool colors such as blue and green are muted.⁴ Hence, these sources are not suitable for shade-matching.

• Fluorescent lights: These light sources emit high concentrations of blue waves.²⁸ They make cool colors such as blue and green appear more intense. Fluorescent bulbs with a color rendering index between 50-80 are unsuitable for shade matching.

• Halogen lights: These light sources emit a bright white light similar to natural daylight, however, they make all colors appear brighter than the original color.⁴⁶

Ideal lighting for shade selection

Natural daylight (Northern) is considered ideal for shade selection as it contains an almost equal blend of all wavelengths of light.^24,44,47 However, ideal conditions may not always be available for shade matching, thus it is recommended to use artificial lighting for color matching.⁴⁸ Natural daylight (Northern) is used as the standard for assessing artificial light sources. For the light source to be suitable for color matching, it should have a color temperature close to 5500 degrees Kelvin and a Colour Rendering Index (CRI) greater than 90.^7,44,49 If natural daylight is unavailable during color matching, a color-corrected fluorescent light with a CRI of 90 or higher should be used in the dental operatory for shade selection..^7,28 However, before finalizing the shade, it is also important to make a note of the various lighting conditions the patients are most exposed to in their daily routine and verify the selected shade under multiple lighting environments.⁷