Hi all,

We have a few fixtures with MSD250/2 lamps, mainly Mac 250+ and Mac 300.

Most of the lamps have lowish power on hours, but a fairly high strike rate, as they are mainly being used in short duration shows.

Just wondering how the number of lamp strikes affects the average operating lifespan of an MSD 250/2

Trying to work out the operating hours before the lamp should be replaced, with a high strike rate, but possible low usage hours.

Hope this makes sense!

Hi

In a nutshell, there really is no way of telling. A high strike count does not always mean a shortened life.

Lamps should be replaced when they approach their hours limit, or when the light output starts to drop off, or when the envelope goes cloudy.

All the best

Timmeh

The strike rate I would have thought is almost irelavent, think of a flourescent tube. they turn on and off thousands of times, but only ware out when the blackening at the ends of the tube, due to hours of use, becomes apparent.

And yes it is wise to change the lamp when it's output becomes yellowed or very low in comparison to the others, as experience will tell that if you leave it too long , you will need to strip the head and use a hoover to remove the remains of the lamp.

Reduced light output is the best guide to replacing discharge lamps, their 'life' is the number of hours for the light output to reduce by half. However, with the MSD 250/2, life is quoted at 2000 - 3000 hours, so the number of hours that the lamp has run can't be used as an accurate guide.

Luckily, there are plenty of cheap light meters on the market, such as this one - Digital light meter from CPC - once you have one of these, and a luminaire with a new lamp in it, measure the output at a set distance - e.g. 5 metres, with open white selected. It's then an easy job to keep a record, a reading every 100 hours should be often enough, perhaps as part of your servicing routine. This will also give you a useful way of finding out how much life is left in a luminaire with unknown lamp hours, handy if you buy used equipment, and your records will be a good sales aid if you choose to sell your equipment.

While a lamp with a high number of strikes will potentially fail sooner than one with less strikes for the same total hours, it's the thermal cycle of the lamp that has greatest effect on overall life. Luminaires that have a remote 'lamp off' function that keeps the fans running for 5 minutes after shut-down, thus allowing steady cool-down, will get better lamp life than those that just switch everything off at once. If you can, having a 'shut down' patch in your lighting desk will take best advantage of this.

Finally, the one thing that kills lamps faster than anything else is poor cooling, so regular cleaning of the luminaire's air vents will pay dividends in extended lamp life.

I have been using 250's in various models from mac's to Robe and honestly its a guessing game, I have had lamps with hundreds and hundreds and hundreds of lamp strikes and stupid amounts of lamp hours, yet I have also had some that one their third strike or so go bang.

I don't go as technical as greenalien does with the light meter but when lined up next to a set of identical fixtures I can usually tell when ones lamp life I coming to an end due to slight changes in in the output.

But this is my own experience for others it may differ greatly.

For fluoros, not so, grasshopper.

See here for a discussion of the mechanisms that determine tube life.

There is an IEEE forumla that works out fluorescent lamp life by number of starts, and if you graph it, it looks a bit like the chart below. Summarizing, the lamps are only good for a fixed number of strikes, and for certain number of total running hours, and when either one expires the fluoro tube is dead.

Assuming the above chart scales to the 2000 hrs life expectancy of an MSD250/2, (which is a big assumption!) then it implies that you should get the full life out of a lamp if you run it for 3 hours each time it's struck, and this will come nowhere near the maximum number of strikes of which it's capable. I wonder if anyone has a similar chart for the actual lamp in question?

One thing I will add - anecdotally, at least, 'genuine' Philips 'Broadway' MSD250/2 lamps last longer than those from other manufacturers - it seems that you get what you pay for!

 A rule of thumb is that a lamp strike will eat up about 3 hours of lamp life. The good new is that quite a bit of these strikes are included in the total lamp life.

One thing to take into consideration is that even if the lamp is rated at 2000 hours, this is not a guaranteed life span.


When manufacturers determine the lifetime of the lamps, they take a bunch of the lamps and leave them to run for a certain time period, they are then doused, allowed to cool down, and then they re-strike them, leave them on for some hours, douse them and so on.. So this is why quite a few lamp strikes are included in the life time of the lamp.

The life time of the lamp is then given at the time were about 50% of the lamps are still functioning.




There is no evidence from any manufacturer that leaving a fixture on with the fan running to allow it to cool down, will give you a longer lifespan. But as others have said, a lamp running to hot due to bad cooling caused by dirty fans, will most likley die sooner then if it was running at the proper temperature.

Slightly OT, but I always though that slower cooling was better as it allowed all the parts of the lamp to cool together, therefore producing less stress on the parts...? The cooling was to prevent all the heat transferring to the other parts of the unit, such as electronics where it could cause harm..?

Yep, overall the lamps would be better off it you just let them cool without fans once turned off. However when you kill power to a fixture, the internal temperature will actually go way UP because the lamp retains heat with it the transfered to the air inside the fixture, cooking the other internal components. Overall it probably is better to force-cool the lamps after dousing to reduce stress on the electronics and optics...

This is what I always thought as well, untill I were shown IR video of a moving light being shut down with fans kept running, and another one whit the plug just beeing pulled. The internal temperature doesn't keep rising for either one of them. They immediately start dropping.