Preheat on dimmer packs with no preheat?

[PhilM]

Is it necessary to preheat lamps which are patched to dimmer packs with no preheat function built in? Perhaps by having the lamps on at a very low level? I'm using an analogue board at my school and it seems almost impossible to have a lantern on at such a low level that it's effect cannot be seen on stage, espcially during blackouts. Also, I'd like to know how nessacery preheating is? I've never preheated anything before... is it good practice?

[niclights]

My understanding is its primary function is to prolong lamp life and prevent premature failure through the shock of sudden heat, notably flashing to full power. It might also help response (rise) time. It shouldn't be too much of a problem to not preheat but try to avoid flashing.

[Renny]

Preheat is purely a plotting thing. For example a cross fade into a state with very different sized lights eg 2Kw back lights and source 4 front light you want to smooth out the crossfade. So therefore preheat the 2K's to make it all happen seamlessly.

 

The auto preheat on Strand boards is a great feature.

[cutlunch]

Philm does the information for your dimmer pack specifally so there is no preheat. Could you please supply the name and make of your dimmers. You may be correct but a lot of packs had this function althouigh you may not be able to alter it. There are a couple of ways to tell if you have pre-heat. One is to plug a lamp into the dimmer with the dimmer power on but the desk channel at zero. Then look into the light with no gel in it and see if you see any glow at all. If there is preheat then you should just see a very faint glow of the filament. If the pre-heat is set right you should only just see the glow. Another thing to check is, if you feel safe using a multimeter, is to measure the output of the dimmer across the live and neutral socket connectors. (This should be done from outside the dimmer pack). The meter should be set on AC 200 -240v range for Britain. If you get a reading between 10 - 20 volts then you have pre-heat.

 

Now back to your question as has already been mentioned pre-heat does save the life of bulbs. Why this is, is when a bulb is cold the filament has a lower resistance. This lower resistance means more current flows when the bulb is turned on. More current means that filament actualy vibrates more and if the filament is ready to fail it this extra vibration may cause it to fail sooner. This why most light bulbs at home blow when you turn them on.

 

If your euipment don't have a pre-heat option there is not much you can do.

 

Before the show do you run all lamps up as a pre-show check then leave them on for a while say at least 10 minutes. This will help a little bit as they will retain some of the heat .

 

Basically pre-heat if you have it will extend the life of the bulbs over no pre-heat and thus save you money.

 

I hope this answers your questions.

[dbuckley]

In my opinion, for straight theatre work, preheat isn't much of a deal, because lamps are usually faded on over a reasonable period of time. However if you're using the flash buttons then preheat can make a big difference to lamp life and to show reliability, which is saying the same thing from a different perspective.

[cutlunch]

Preheat is purely a plotting thing. For example a cross fade into a state with very different sized lights eg 2Kw back lights and source 4 front light you want to smooth out the crossfade. So therefore preheat the 2K's to make it all happen seamlessly.

 

The auto preheat on Strand boards is a great feature.

 

 

 

I have never heard of this before. As you will see from my post I believe it is about lamp life. I don't see how your arguement works except for snap crossfades. Because if you are crossfading using a timed cross fade the lamps comming up are heating as their level rises.

 

Could you please explain your arguement more fully and/or provide a reference source because if I am wrong I like to learn from my mistakes.

 

Thanks

[mac.calder]

Even if a dimmer pack does not have a pre-heat function, it is easy enough to do. The way I usually do it is as follows:

 

Put the master fader down to 0.

Put all channel faders to about 40%.

If you have a time-in fader or pot, give it the maximum fade in time.

Move the grand master to full - if you don't have a fade-in timer, do this slowly, over a couple of minutes. Leave them at full for a few minutes.

Then bring the grand master down to 0 again, set all faders to 100% and move the grand master back to full - either using fade in time set full, or by slowly fading the grand master.

 

Voila, everything will be warm, and they usually stay quite warm for a decent ammount of time. However if you have a one use only special that happens quite a distance in and you are worried about blowing a bubble due to cold fillament, I believe most dimmers 'pre-heat'/'keep warm' functions use 3% or there abouts as their 'pre-heat' warmth.

 

That said, after a while, up there will be quite hot, so the lamps are kept warm through the ambient heat.

 

--As an asside--

 

The purpose of preheat is to reduce the stress on the bubbles fillament. It also helps even out the responses of lanterns - cold lanterns tend to fade far less smoothly at the lower end of the scale.

 

The main problems come with using bump/flash buttons. Flashing a cold lantern is one of the best ways to blow bubbles. Anyone who has ever flashed a cold par rig on a cold morning would probably know all too well the problems faced - although PAR's are usually pretty good... The old Patt23's are probably the worst I have seen.

[Jivemaster]

For theatre with long cues and fade rates pre-heat is of little value/need.

 

For Rock n Roll with flashing lights then about 3 - 5 % preheat prolongs the (flash reduced) lamp life.

 

If you haven't auto preheat, for theatre -ignore preheat, BUT for RnR push the fader up to 5% ish and use the flash buttons for the chases. ( An Lx op tapping his fingers to the music is probably actually doing the chases live real time- which looks so much better than auto! )

[GridGirl]

I don't usually bother with preheat - as others have said, warm the rig before a show and you should be OK unless it's a one-use special. The only lanterns I tend to preheat during a show is anything with a glass gobo in it - and that's purely so the gobo doesn't break with the temperature change when it goes to full! I tend to do this even when I'm using a cool-beam light like the Selecon Pacific.

[Jamtastic3]

Before doing bands, usually in the soundcheck I'll preheat the par rig by bringing the Master to 0% bringing all the faders to 100% then gradually move the Master to around 10-15% and keep it there for 10 minutes - then reset and start programming.

[PhilM]

Thanks for all the advice guys. I can't remember the brand and make of our dimmer packs off hand I'm afraid. Will check this on Monday and also check the voltage. I always do a pre-show check so I guess there's not a lot of reason for concern.

 

Thanks!

[Renny]

I have never heard of this before. As you will see from my post I believe it is about lamp life. I don't see how your arguement works except for snap crossfades. Because if you are crossfading using a timed cross fade the lamps comming up are heating as their level rises.

 

Could you please explain your arguement more fully and/or provide a reference source because if I am wrong I like to learn from my mistakes.

 

Thanks

 

No scientific or printed reference but many years of plotting for good lighting designers. As for the point about it only being essential for snaps crossfades (sic) try fading up a state that for example has a bar made up of 500w floods as part of the rig and see if they don't race ahead of the rest of the state. Can be a nice effect but not really that desirable normally. A bit of time spent working out a preheat group on a Strand 500 series can save a lot of fiddling around in plotting. Or if you want to be fiddly you can achieve the same end result by plotting part cues to make relevant bits of the state come up at different speeds.

[niclights]

Totally offtopic, but surely dimmer curves are used for that? Preheat is there to save lamps.

[Nick S]

Re flashing lanterns: Student comes into theatre after summer holidays, turns on board, flashes all the lights. That's a sound I don't want to hear ever again...

 

A bit of time spent working out a preheat group on a Strand 500 series can save a lot of fiddling around in plotting. Or if you want to be fiddly you can achieve the same end result by plotting part cues to make relevant bits of the state come up at different speeds.

 

Or perhaps use the profile editor? ...I mean, that is what it's designed for...

[Renny]

Re flashing lanterns: Student comes into theatre after summer holidays, turns on board, flashes all the lights. That's a sound I don't want to hear ever again...

 

Or perhaps use the profile editor? ...I mean, that is what it's designed for...

 

Yes you can fiddle with the profile editor or dimmer curves. However surely the quick simple option is easiest? For example if you are receiving a lot of shows do you have the time to alter profiles for every rig you put up? I understand the logic of extending lamp life but that is less important nowadays in these times of digital dimming which by its very nature is kinded to lamps filaments with smoother curves as the norm. In the past I have toured shows in tents with analogue dimmers where you have to crank the preheat at the dimmers up so far that you have a faint glow on every lantern when you look into the lens. All I am saying is that nowadays the only time I preheat is to aid plotting.

 

Then again I work in theatre where people flashing lanterns constantly isn't really normal for shows and crossfades generally the nature of the beast.