[devindotcom]

It doesn't seem too strange to use a scale that corresponds to commonly-encountered heat levels, as perceived - yellow, orange, red, white, blue or something - it's not exactly logical, but people grasp it quickly because it has a familiar analogue. You could use a plain luminosity based presentation, but that's not the way humans have experienced heat for the last 40,000 years. It may not be mathematically perfect, but it's what we've got.