why lamp off?

[alabamaman]

Hi everyone,

My question could look silly, but I would like to have an explanation about the use of the lamp off command on a moving head. What's the difference between that and simply uncable the moving head? What happens exactly and why is it better to use lamp off?

[LXbydesign]

The lamp off command is there to enable you to switch of the lamp (funny that) if the fixture is not going to be used for a while (for example, over a lunch break or inbetween shows etc).

 

Its better to use this function as so then the remains of the fixture is still on and the fans aid with cooling down the unit. it also saves having to turn the units off from the mains and powerering back on - doing a reset and so forth.

 

If you only have a few movers, I suppose its nether here or there really how you do it, but with bigger rigs and supplies maybe coming from different areas, the remote lamp off is very useful.

[mrcog]

I've always been under the impression that the lamp of function preserves the life of the lamp because you've still got the fans running to keep the lamp cool?

[paulears]

It's simply the lighting equivalent of standby on a TV. At the price of discharge lamps, a few hours here and there make sense, as well as reducing heat output when you have lots.

 

Many people like to send a lamp off command to the entire rig at the end of a show, then when they've all cooled down, flip the power off. I'm not sure anyone really has spent time and effort calculating the X% of extra lamp life, but it's probably just a good practice.

[gareth]

Turning your moving head lamps off is worthwhile for a break in proceedings of an hour or more (a semi-arbitrary figure based on what little information could be gleaned out of a technical bod at Osram regarding how much got knocked off the useful life of a lamp every time it was struck!!) - a meal break, for example. If you're just stopping for a 20-minute coffee break, the benefit of dousing your lamps is cancelled out by having to re-strike them again after a very short time - in that situation, just take everything (colours, gobos, effects, etc.) out of the beam and leave the shutters open to allow the units to stay as cool as possible with the lamps still on.

[son of lx dad]

From a purely practical physical point of view, doing a lamp off and letting the fans do the cooling rather than just killing them helps a lot when physically loading out 20mins later. Saves an ouch or two and a melted flightcase interior.

 

I remember a time when glass reflectors at high temps were more volatile to breaking when you chucked the heads in the box.

[ColourBlack]

In the old Vari*Lite days, it was suggested that if the system was is standby for more than 2 hours (dimmer closed, lamps in standby) then the system should be doused. If it's less, then as Gareth says, leaving the units with the dimmers open, in Open White, Pointing straight down is pretty good practice. Though there is the argument that when the dimmers are open the lamps will be running at 100%, and when the dimmer is closed they'll be in Standby....

 

Restriking lamps takes a big toll on the lifespan, so the fewer restrikes the better.

 

As Paul says, at the end of the show it's good practice. My post show 'cockpit drill' is 'Release' the rig (so kill all active cues), douse the system, GM / All Faders down, shut down the desk - and after 5-10mins or so switch off the system. An old VL habit.

 

P

[GRisdale]

I'm not sure anyone really has spent time and effort calculating the X% of extra lamp life, but it's probably just a good practice.

A former Martin technician, now working for White Light's technical department, reckoned that each strike of a discharge lamp costs about 4 hours of lamp life (according to Martin a few years ago anyway...)

 

Gareth.

[gareth]

A former Martin technician, now working for White Light's technical department, reckoned that each strike of a discharge lamp costs about 4 hours of lamp life (according to Martin a few years ago anyway...)

I'd be genuinely interested to know where he got that specific figure from. A while ago we at work were wondering whether such a thing was actually quantifiable, and no-one from the major lamp manufacturers would be drawn on an actual figure ...

[paulears]

That's pretty much what I'd found - I suspect that there really isn't any empirical data on this, just people's personal opinion based on their own experience and the opinion of others they respect. Basically dodgy data, but data that sounds kind of right?

[Ashley R]

I thought it was more like 2 hours every time you re struck the lamps?

 

And if you send a Lamp off command the fixtures cool down so much faster than a simple turn off the power. In my opinion that is much better for the lamp, because straight after you turn off the fixture the lamp is still red hot and before you turned off the fixture there was a fan there to help keep the lamp cool, now this fan is no longer operational and the lamp is heating up above its preferred temperature.

 

well that's my explanation anyway.

[mac500]

Also having them point straight down puts all the heat out of the back of the lamphouse straight into the base so its best to point them somewhere to avoid that.

[paulears]

there was a fan there to help keep the lamp cool, now this fan is no longer operational and the lamp is heating up above its preferred temperature.

Once the power is off, the lamp cannot heat up without an energy source. What is true is that the fans help to cool the fixture down once power is off, so killing power means a longer period to cool, that's all.

[gyro_gearloose]

My understanding has always been that the metal electrodes run considerably hotter than the rest of the lamp, as while the fans are running the heat is constantly being carried away. If you power off without leaving the fans running, the heat from the electrodes is transferred to the rest of the lamp. I doubt it makes much difference even on something like an HMI1200 as the electrodes are quite small. However the 1600W Xenon lamp in the cinema projector at work has electrodes the size of my thumb which hold a considerable amount of heat.

[Ashley R]

there was a fan there to help keep the lamp cool, now this fan is no longer operational and the lamp is heating up above its preferred temperature.

Once the power is off, the lamp cannot heat up without an energy source. What is true is that the fans help to cool the fixture down once power is off, so killing power means a longer period to cool, that's all.

 

But there will be stored energy in the electrodes will continue to disapate heat once the fixture is switched off? So the external tempreture will be cool when the fan is running but will soon heat up because of the energy stored in the lamp and in the houseing surrounding it.

 

Im not sure if ive explained this very well but it makes scence in my mind. And what Gyro_gearloose said is basically what im trying to say.