We never had to think about kelvins when buying light bulbs in the past, so why now?
Kelvins became a thing when LED lamps were introduced because they can produce different temperatures of light unlike incandescent and halogens that can only produce the warm glow of yellow unless you use coloured glass.
When you buy an LED lamp there will be information printed on the lamp packaging with will tell you the kelvins temperature of the lamp, it will either be displayed as numbers with a prefix K ie. 2700K or it will describe the colour in two words ie. Warm white.
The following types are the most popular with consumers.
2700K or Warm white gives off a warm yellow/orange light, similar to old style light bulbs.
Mainly used in living rooms and bedrooms
4000K of White light, gives off a very clean crisp white light, this would be mainly used in kitchens and outdoor lighting.
6200K or Daylight, this is a very bright light with a touch of blue in it, this is similar to the light you get on a bright day outside, this colour would typically be used in retail environments.