Moved to the Lightroom Ecosystem forum.
The Kelvin scale measures the colour temperature, which has nothing to do with temperature in the traditional section.
Daylight is 5500 Kelvin (though Lightroom has an internal scale which is different than camera makers), Tungsten is around 3300k. Raw files use this scale as it gives greater and more accurate control using the sensor data. The -100/+100 scale is for rendered files and will actually reduce quality on export as you're manipulating pixel data rather than sensor data.
Sean McCormack. Author of 'Essential Development 3'. Magazine Writer. Former Official Fuji X-Photographer.