> It's not especially close to the peak sensitivity The sensitivity at sodium light is above 75% of the peak human vision (photopic) sensitivity. This is a ve

> It's not especially close to the peak sensitivity The sensitivity at sodium light is above 75% of the peak human vision (photopic) sensitivity. This is a very small difference in light sensitivity. For example in the case of many sources of red light or blue light the sensitivity can be 5 to 10 times lower than the peak sensitivity. Moreover, a perfect source of white light cannot achieve a better sensitivity than around 37%, i.e. less than half of the efficiency of an ideal source of monochromatic light at the sodium emission line. Therefore the fact that currently LED lamps and low-pressure sodium lamps have about the same energy efficiency is caused by the LED lamps having a higher photonic efficiency and a lower threshold voltage (caused by a P-N junction voltage instead of the ionization potential of sodium), which compensate the disadvantage of using white light. A monochromatic LED lamp with the same color as the sodium lamps could have an energy efficiency at least double over the white LED lamps.