Excellent lamps, reliable with an average lifespan of 32,000 hours, which means with daily use averaging 10-12 hours as used in municipal lighting, they will last about 9-12 years, which is the usual durability of these lamps and in some cases a little longer, but the brightness will typically decrease by 17-22%. That is, if it is 400W, where this particular one has an efficiency of about 130-135lm/watt and its brightness is at 56,000 lumens, which is ideal for a three-lane highway or in huge spaces of 450-560 sq.m, ideally at the end of its life the brightness instead of 56,000lm will drop to about 44,000-48,000lm. The reduction will not be very noticeable but it is likely to be perceived, however, this is normal as even LEDs will show a similar decrease in performance, in a few cases they may have better performance at the end of their life but usually similar or even worse performance at the end! High pressure sodium lamps emit an intense golden-yellow-orange light which is excellent in low visibility conditions, e.g. fog. The yellow-orange light of high pressure sodium lamps has strong penetration in fog and the light can pass through and generally be more visible in fog compared to white light. However, it is not intended for all applications and especially for indoor spaces where their use is limited because the golden-yellow light of high pressure sodium lamps creates quite intense color distortion due to the low color rendering index, which is only between 20 and 30, while light sources are usually above 75-80 CRI, which is why these lamps are not intended for all applications