Question

For the highest temperature, is more of the intensity (area of the intensity vs. wavelength graph) in the visible part of the spectrum or in the infrared part of the spectrum? How could a light bulb be made more efficient so it puts out more light in the visible?

Answer 1

Amazingly all matter in the universe gives off light at every wavelength from gamma rays to radio but we give off a lot more of certain kinds of light based on our temperature. This is called blackbody radiation and a graph of how much light comes in at each temperature is called an object's blackbody curve. The blackbody curve peaks at different wavelengths depending on its temperature. Higher energy light has shorter wavelengths so the higher object's temperature the shorter wavelength light the blackbody curve peaks at. Cool objects like planets, brown dwarfs, even you and me peak in infrared light. Higher objects glow in visible light and some objects that the inner discs around black holes or gamma ray burster are so hot that they actually shine an x-ray or gamma-ray light.

Coming to the second part of question i.e. How could a light bulb be made more efficient so it puts out more light in the visible?

The key is to create a two-stage process, the researchers report. The first stage involves a conventional heated metal filament, with all its attendant losses. But instead of allowing the waste heat to dissipate in the form of infrared radiation, secondary structures surrounding the filament capture this radiation and reflect it back to the filament to be re-absorbed and re-emitted as visible light. These structures, a form of photonic crystal, are made of Earth-abundant elements and can be made using conventional material-deposition technology.

That second step makes a dramatic difference in how efficiently the system converts light into electricity. The efficiency of conventional incandescent lights is between 2 and 3 percent, while that of fluorescents (including CFLs) is currently between 7 and 13 percent, and that of LEDs between 5 and 13 percent. In contrast, the new two-stage incandescents could reach efficiencies as high as 40 percent.