The “colour” of a light source comes from a complicated relationship derived from a number of different measurements, including correlated colour temperature (CCT), colour rendering index (CRI) and spectral distribution. In general, colour is most accurately described by a combination of CCT and CRI.
Correlated Colour Temperature (CCT)
The first factor in choosing a lamp colour is the correlated colour temperature. For example, if a retailer wants lighting to blend in with warm halogen accent lamps, they could select to use a Venture® HIPE 100W/C/U/LU/UVS/3K, which has a correlated colour temperature of 3200K. CCT is defined as the absolute temperature (expressed in degrees Kelvin) of a theoretical black body whose chromaticity most nearly resembles that of the light source. The CCT rating is an indication of how “warm” or “cool” the light source appears. The higher the number, the cooler the lamp colour will appear. The lower the number, the warmer the lamp colour will appear.
Spectral Energy Distribution
When we look at a light source, the eye “perceives” a single colour. In reality, we are seeing literally thousands of colours and hues made up of a combination of different wavelengths of light. These different combinations and the relative intensity of various wavelengths of light are used to determine the CRI of a light source.
Colour Rendering Index (CRI or Ra)
In general, CRI is a numeric indication of a lamp’s ability to render individual colours accurately relative to a standard. The CRI value is derived from a comparison of the lamp’s spectral distribution to the standard (e.g. a black body or the daytime sky) at the same colour temperature.
Colour Shift and Variation
Different colours are produced in metal halide lamps by using various arc tube shapes and metal halide salts. In new lamps these halides need to “burn-in” for approximately 100 hours before they reach their optimum colour. This is why new lamps can sometimes be unstable or vary in colour. As metal halide lamps age, chemical changes occur causing shifts in colour. Generally, traditional probe start lamps shift approximately twice as much in CCT over life compared to Uni-Form® Pulse Start lamps.
Designer Colour® lamps that produce blue, green, aqua and pink light are available for special applications where colour is needed without light loss due to filters.
Venture Lighting offers lamps in many colours to suit virtually any lighting application. Outlined below are the various colour temperatures (CCT) currently available:
- 27K 2700K (a replacement for very warm incandescent lamps—coated only).
- 3K 3000K – 3200K (a general warm, white light source, available in clear or coated finish for retail or interior applications—blends with halogen lamps).
- 4K 3700K – 4000K (a neutral white light source, available in clear or coated finish for general lighting, factories, parking lots, warehouses).
- 5K 5000K (a moderately high CCT daylight source used in general and retail lighting applications).
- 6K 6500K (a high CCT daylight source used to simulate average outdoor light conditions).
- 10K 10000K (a very high CCT, daylight light source, used in horticulture and aquarium applications).