The light emitted by any lamp (led, neon, etc) is perceived by the human eye with a color gradation. If this rate is tending toward the red tones, the light is called WARM (English WARM); if the alcohol content tends toward blue, it's called a COLD (in English COOL).
This color is measured in DEGREES KELVIN, that is why we speak of the COLOR TEMPERATURE.
With traditional bulbs incandescent or halogen bulbs you couldn't choose the color of the light the bulb produced. The bulbs worked with the passage of electricity through a wire that overheats and becoming red. This glow, producing light. Since the LED bulbs use a different technology and much more advanced, you can choose the shade of color that you want.
Without getting too technical, the color temperature of the light can be expressed with a number on the Kelvin scale. This is represented by a number followed by the symbol "K".
High colour temperatures of 5000K and over it says that the colors are cold and often take on a blue hue.
At low temperatures color 2500 - 3200K says that warm colours, and take on tones of yellow or orange.
Conventionally, according to UNI 12464, we speak of:
Or Warm white light warm (English WARM WHITE), if the color temperature is lower than 3300 K,
Neutral white or natural light, such as sunlight at noon (in English, NATURAL) if the color temperature is between 3300 and 5300 K,
Cool or cold light, in English, COOL WHITE), if the color temperature is higher than 5300 K.