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sodium lamps emit their light very near to the peak sensitivity of the human eye under normal viewing conditions, this fact accounting for their remarkably high luminous efficacy The light emitted is monochromatic, i.e. it is comprised of only one colour Incandescent lamps produce light of all colours over the entire visible range 400 to 700 nanometres (nm), so these have good colour rendering properties. Other light sources produce light at many different discrete wavelengths and all provide some degree of colour rendering However, sodium light is almost totally made up from deep yellow wavelengths at 589.0 and 589.6nm, so no colour rendering is possible While this does not cause a problem on main roads, it may be unacceptable in other areas such as town centres and it totally precludes the use of this light source for interior lighting or in any place where colour rendering is required The spectral power distribution of the low pressure sodium lamp is compared with several other common light sources, as well as Daylight.
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