Recently, I was wonder if there is a way to increase the lifespan of high pressure sodium bulbs. Is this possible in anyway? If so, would using, for example, a 310W HPS bulb on a 250W HPS ballast increase lifespan of the bulb when run dusk to dawn?

Usually, you can prolong the life of a HID lamp by reducing the power to about 2/3 of nominal. But in the most cases, until you run some special type of lamp like tin type or unsaturated metal halide for example, you quickly end up with a bad color. In the case of HPS lamps, CRI drops considerably already over nominal line voltage variations!

So would operating a 310W HPS bulb on a 250W HPS ballast increase lifespan? By how much? Color and lumen output is not a concern.

I have a Dali dimmable 70w SON sitting around. Been meaning to hook it up for a while now, i'll report when i do, it can dim to 50% afaik.

Buuuuuuuut


HPS lasts extremely long as it is. It is not really something i would worry about.

By how much?

I doubt anyone can tell you exactly. Not even a lamp manufacturer, until a series of lifetime tests were run, which is very time-consuming (obviously) and expensive.

Generally, physical/chemical processes that limit the lamp lifetime, arctube corrosion, sodium migration, electrode sputtering and so, should follow Arrhenius law, meaning that decreasing of the temperature will slow down them. But, decreasing vapor pressure will promote sputtering. Also, decreasing electrode temperature will decrease electron emission, and in the end, increase cathode drop, ion bombardment, and finally, sputtering.

Lifetime vs power curve is well-known for simple tungsten incandescents, but things are much more complicated in discharge lamps.