CCT (Color temperature)
The color temperature is expressed in Kelvins. It is characteristics of the energy distribution of the radiation within the different wave lengths that make up the luminous source emission spectrum.
The more the light tends towards white/blue (10.000K), the more it is said to be “cool”. (White 4.000K, cool white 5.000K, industrial white > 6.000K). The more the light tends towards yellow/orange (0K), the more it is said to be “warm” (warm white 2.700 to 3000K).
The Color Rendering Index is the capacity of a light source to reproduce the different colors of the visible spectrum without modifying the shades. The general color rendering, Ra, determines the quality of a light based on the rendering index of 8 standardized colors. The maximum index, 100, corresponds to a white light with the same spectrum as that of the sunlight.
Lumens and candela:
Lumen is the unit that measures the luminous power emitted by a source (or flux). The candela is the SI unit of luminous intensity; that is, power emitted by a light source. The Lumen/Watts is an index which indicates the bulb or spotlight’s luminous output (efficiency). A luminous source’s output is major characteristic, especially these days when it is long lasting development issue.
Comment: How much does my bulb consumes and for how much reproduced luminous power? The LED luminous sources available to the general public have an efficiency that varies from 25 lumens/watt to 80lumens/watt. This means that I shall consume 1 watt of electricity to obtain 25 to 80 lumens. In comparison, the luminous efficiency of an incandescent bulb is around 5 lumens/watt.