The luminous efficiency of a 5000 K incandescent halogen bulb can be greater than a 3000 K bulb. The 5000 K Osram bulb discussed by Bruce Abbott is an auto head lamp. The listed 5000 K is CCT, correlated color temperature. This means the light emitted from the bulb is not a true blackbody spectrum. To the eye, it appears similar in color of a blackbody at 5000 K. The filament cannot be at 5000 K because tungsten melts at 3695 K.
The higher CCT, is accomplished by filtering out the infrared, red and orange by the color filter on the glass bulb. The filter most likely is a recycling filter that reflects the light (IR, red, and orange) back to the filter where it is reabsorbed, making the filament hotter and more efficient than the 3000K bulb. The filter is made to tolerate high temperature. The quartz bulb temperature is between 250 and 525 C525°C, where halogen tungsten recycling works. The filament temperature is most likely between 3100 and 3200 K.
If both bulbs were originally designed for a filament that operates at 3000 K, than adding a recycling filter makes the filament hotter, have a higher CCT and more efficient.
