PH5 was introduced in 1958 by Louis Poulsen.
Poul Henningsen wanted the PH5 to improve the quality of the light, because the incandescent lamp light had not improved significantly since the invention.
The lamp had, therefore, small red, and blue screens, which should give a color contribution of the part of the spectrum where the eye is least sensitive - and attenuate light in the center area, where the eye is most sensitive, that it is yellow-green. The strong "management" of the quality of light and lamp design not to dazzle the viewer went hard at the amount of light emitted.
Over time there has been changed slightly on the lamp so it gives a little more light.
You might see a little difference of the amount of light between the two lamps shown.