Me semble qu'au delà de la luminosité, qui peut se vérifier au luxmètre, c'est surtout une déformation du spectre qui pose problème, avec entre autre des IR et UV a la ramasse.
Nav T 4y ici aussi
EDIT :
At end of life, high-pressure sodium (HPS) lamps exhibit a phenomenon known as cycling, caused by a loss of sodium in the arc. Sodium is a highly reactive element and is lost in a reaction with the aluminum oxide of the arc tube. The products are sodium oxide and aluminum:
6 Na + Al2O3 → 3 Na2O + 2 Al
As a result, these lamps can be started at a relatively low voltage, but, as they heat up during operation, the internal gas pressure within the arc tube rises, and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the maximum voltage output by the electrical ballast. As the lamp heats to this point, the arc fails, and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, typically starting at a pure or bluish white then moving to a red-orange before going out.
More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles, as the repeated high-voltage ignitions needed to restart the arc reduce the lifetime of the ballast. If power is removed and reapplied, the ballast will make a new series of startup attempts.
LPS lamp failure does not result in cycling; rather, the lamp will simply not strike or will maintain the dull red glow of the start-up phase. In another failure mode, a tiny puncture of the arc tube leaks some of the sodium vapor into the outer vacuum bulb. The sodium condenses and creates a mirror on the outer glass, partially obscuring the arc tube. The lamp often continues operating normally, but much of the light generated is obscured by the sodium coating, providing no illumination.
Donc , de ce que j'en comprend, une lampe en fin de vie demandera moins de jus a l'allumage et plus en fonctionnement, obligeant le ballast a se mettre en sécu et a se réamorcer. Egalement les dépots de sodium qui obscurcisse le tube et diminue du coup la luminosité ?!
)
mais pour le coté bleuté je parlais de l'ampoule