Osram Dulux S 9W 835

The cap/base of a bulb is the part that connects it to the socket in the fixture. In the UK, B22 (Bayonet) caps/bases are still the most popular, although E27 (Edison screw) caps/bases are becoming increasingly popular. GU10 is the most common cap/base for spotlights. Check which cap/base you need carefully as many other types are also available.

The colour temperature refers to the colour produced by a light. It's measured in Kelvin (K) and ranges from warm white (1700K - 3000K) to daylight white (6500K). Neutral white (3100K - 5000K) is mainly used for general lighting applications.

The colour code is a combination of the colour rendering index (CRI) and the colour temperature (K). The first number refers to the CRI (1 = very poor colour rendering, 9 = maximum accuracy). The second and third numbers refer to the colour temperature. For example, a light with a colour code of 830 has very good colour rendering and produces a warm white light.

The colour rendering index (CRI) indicates how accurately colours are represented under a beam of light. The index goes from 1 to 99, with a CRI of 1 being the poorest and a CRI of 99 being the best possible. Be careful not to confuse colour rendering with colour temperature (K).