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HMI safety precautions and using gels on strong lights


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#1 Andy Rance

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Posted 03 January 2009 - 06:18 AM

Hey everyone, I'm working as a DP for a short film to be shot In February, and I'm in the early stages of planning the lighting design. The film takes place almost entirely in a forest at night, and it will have to be filmed in a forest at night no matter what (no day for night is possible due to the limitations on shooting hours that the county permits give). We're shooting on the RED one in 4K RAW and have a modest budget at our disposal. I originally was going to use 6k, 4k, 1.2k and 575w HMI's, some diffused and some not, and some weak fills here and there. Some of the lights were going to be placed on really high stands and trees (at about 20- 24 feet), to simulate the direction of moonlight (we can't afford cranes). My plan was to set the RED one's manual color temp controls to around 4500K, and as a result of the roughly 5600K color temp of the HMI's, automatically get weak blue 'moonlit' tones on camera without having to worry about placing and looking after blue gels on lights at such high altitudes.

Although I had read about HMI's occasionally exploding violently near the end of their lifespan or when they're dropped, it didn't concern me too much until I really looked into the type of crew I'm dealing with for the shoot. Most of the Gaffers and Grips on the set have a fair amount, but not too much experience. Because of their limited experience, I'm considering using Mole 5k, 2k and 1k Fresnels and other types of lights instead of the HMI's, to avoid any 'explosions' or 'harmful UV effects' or any other problems the HMI's may present. Now that automatically presents some problems for me, since now I would probably have to color correct the lights to get a tint of blue, and I have doubts about how the color correcting gels would hold up if placed in gel frames so closely to strong lights such as 5k Fresnels.

So my questions are:

Do HMI's usually present many problems to film crews?
Is it recommended that a crew like the one I described above use them at 20 to 25 feet off the ground, with cables, generators and more at night?
Is it better to just go with the Fresnels instead and avoid any potential problems with the HMI's?

and...

If I do use a lighting setup with the fresnels, what's the recommended distance that a gel should be from a 5k or 2k fresnel, where it won't end up melting?

Any help would be greatly appreciated. Thanks a lot!
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#2 timHealy

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Posted 03 January 2009 - 09:39 AM

I have been an electrician for almost 20 years and I think I have seen HMI's bulbs blow up perhaps 4 or 5 times form a 4k to 12 or 18k's.

It has been more common for a tungsten lamp to explode, but then again, tungsten is used more than HMI's on a typical job, especially if there is a stage rig.

You can use HMI's or tungsten for your job. It comes down to creative and financial choices, and power availability(which may be part of the financial decisions. Generally speaking most older and experienced DP's will use tungsten at night most of the time. Younger DP's will use HMI's for an easy blue effect most of the time. If budget is a huge concern, a DP might have one 18k on a truck instead of one 18 for day work and one 20 k for night work. There are a lot of variables here.

If power is a concern HMI's will put out more light than a comparable tungsten lamp.
If financing is tight then Tungsten lamps are cheaper to rent, but you may wind up needing more power to get the same lighting.

HMI's can be more troublesome and susceptible to weather than tungsten, but with proper use and protection will be fine.

Either way you go using HMI or tungsten par's instead of fresnels will give you more light to work with. And most HMI Par come with a fresnel lens if you want to use it in that manner. Since tungsten pars only go up to 1k, (or 1200 watts for a fire starter bulb) I mean for you to use a 9 or 12 light maxi instead of a 6k par or the like.

As far as gels go, you should be fine using gels in front of most fresnels as long as the gels don't touch each other if you have more than one layer. They will melt together if they get hot and the layers touch each other. Using gels with narrow or very narrow pars you will need a layer of heat shield to make the gel last longer.

I hope this helps.

and I hope your crew doesn't read cinematography.com.

Best

Tim
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#3 Rob van Gelder

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Posted 03 January 2009 - 12:14 PM

Hi Andy, from what i know about the Red One camera is that is favors blue-ish light for best performance, so a preference for HMI.
So that might be your basic starting point, because if you choose Tungsten, you might have to gel that so much or accept the increased noise in the blue channel.

In my opinion, the modern HMI equipment is at least as reliable as Tungsten, but please use the electronic, flicker free ballasts, if possible with power factor correction circuit as you will have you crew laying loooong cables through the woods.

and as for Tungsten Par lamps, Mole-Richardson has a very nice 5Kw Par available now.

Rob
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#4 freddie bonfanti

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Posted 03 January 2009 - 04:57 PM

hi,

i kind of understand why you'd be rather using tungsten than HMIs, but as Tim said HMIs arent as bad as you think. ive seen more tungsten bulbs going off that HMI ones, sometimes a few old HMI lamps with a fault in the micro switch system, but if you know how to use them properly it should be fine.

the other real advantage with tungsten a part from being cheaper and less "fidgety" is that you always get the right color temperature, something that is often hard to get with HMIs, especially the smaller heads IMO.

anyway no matter what lamp you will be using when dealing with electrics there is no easier way, make sure things are safe and secure
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#5 timHealy

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Posted 04 January 2009 - 06:52 PM

and as for Tungsten Par lamps, Mole-Richardson has a very nice 5Kw Par available now.

Rob


Oh yeah I forgot about those, but for some real focusable tungsten heat I would prefer a Ruby Seven with 1200 watt firestarters. That is a great light unless someone pulls out an 18k Arrimax.

best

Tim

Edited by timHealy, 04 January 2009 - 06:55 PM.

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#6 timHealy

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Posted 04 January 2009 - 06:56 PM

is that you always get the right color temperature, something that is often hard to get with HMIs, especially the smaller heads IMO.


Color temp is a good point Freddie.

best

Tim
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#7 Brandon J Barron

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Posted 05 January 2009 - 04:20 PM

Another thing I would consider is, while putting lights 25-30 feet off the ground isn't what I would classify as uncommon as we all know, if you could use tungsten and move some of that HMI rental money towards a more experienced gaffer to CYA on the safety thing that might be something to look into. Just a thought. Good luck and let us know how it goes.

_brandon barron
www.brandonbarron.com
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#8 chris evans

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Posted 12 January 2009 - 05:58 PM

You should also think about equipment check out. While your crew checks the working order of the equipment, they have an opportunity at the rental house to ask questions. This is also the perfect time to color temp your HMI heads as well as build frames (CTO; CTB; -GRN) to correct any that are off.

Most Gaffers and DPs won't use a head that has a color temp of 4900k or below. At this point, the bulb is pretty green and would have burned approximately 700-1000 hours and should be swapped for a new one. The reason for the gap is that some bulbs begin their life after settling at either 6000k or 5600k, and if you don't know which, why take the chance.

But definitely ask questions at the rental house during check out.

Good luck!

Chris
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#9 Daniel Porto

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Posted 16 January 2009 - 07:34 AM

When attaching gels make sure that you let the hot air escape through the top. So attach your gels to the side barn-doors and not the top and bottom so that the hot air can escape and it will stop your gels from melting 99% of the time
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#10 Derek Leffew

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Posted 16 January 2009 - 10:23 PM

When attaching gels make sure that you let the hot air escape through the top. So attach your gels to the side barn-doors and not the top and bottom so that the hot air can escape and it will stop your gels from melting 99% of the time

Agree with the above. As long as the color/correction media is attached with clothespins to the side, and not the top and bottom, leaves of the barndoor you shouldn't have any problems with burn-through, although dark colors may fade after ten or more hours of constant use.

HMI fixtures require no more safety precautions than incandescent fixtures. Explosions are extremely rare, and "harmful UV radiation" is removed by the glass lens.
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#11 timHealy

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Posted 17 January 2009 - 03:38 PM

HMI fixtures require no more safety precautions than incandescent fixtures.


Actually they do. A tungsten lamp can be a little more hardy in wet conditions, where an HMI must have it's ballast, head, and header cable connections protected. Look at an Maxi brute for example. In a light rain you could get away with using no rain protection. With the right connection, tungsten par bulbs will even work underwater. While an HMI with all it electronics needs to be seriously protected in any sort of rain. I don't advocate not using rain protection on any lamp, it is just that HMI's need to be seriously protected if you want the lamp to continue working.

Best

Tim

Edited by timHealy, 17 January 2009 - 03:39 PM.

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