Color Temperature is not how hot the lamp is. Color temperature is the relative whiteness of a piece of tungsten steel heated to that temperature in degrees Kelvin. For example, High Pressure Sodium lamps (HPS) have a warm (red) color temperature of around 2700K as compared to Metal Halide (MH) at 4200K, which has a cool (blue) color temperature. Daylight spectrum bulbs most closely replicate the sun’s temperature at 6500K.
Lumen is a measurement of light output. It refers to the amount of light emitted by one candle that falls on one square foot of surface located at a distance of one foot from the candle. Traditionally, lumens have been the unit of visible light emitted from a source, usually referring to indoor lighting for humans; meaning the brighter the lamp the greater the output. However, studies have shown that a broader color spectrum lamp will perform much better than a lamp with high lumen output, especially when it comes to plant growth. More commonly, light for horticulture applications is measured in PPFD, or the amount of photosynthetically available light over one square meter per second.