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    HMI: how not to die
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    Senior Member djkarn105's Avatar
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    So I'm gaffing for a low budget indie next month and we'll be using some HMI's. I haven't touched one since that one time in film school. What do I need to know so I don't kill myself and other (or get fired).
    Last edited by djkarn105; 03-29-2011 at 10:08 AM.
    "Without the Chaos, there would be no happy accidents"


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    Don't remove the UV protection, as doing so can cause permanent eye damage to those in front of it. Generally they are designed to not let you operate the lamp without the protection in place, but it's best to verify this.


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    Moderator David Jimerson's Avatar
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    Don't shut one off and expect to turn it right back on again.
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    Cinematography/Lighting Mod Ryan Patrick O'Hara's Avatar
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    1) Never touch the globe with your bare hands, the oil on your skin will cause the bulb to further rise in operating temperture and possibly explode.
    2) Make sure everything is off when you connect the header cable to ballast, and ballast to wall. Turn power switches on, in appropriate order to the light head.
    3) Allow the HMI about 7 min to get to full strength and correct color temperature.
    4) HMI bulbs are supposed to be 5600k, but are handmade and vary with lifetime, so it would be wise to have a color meter, if available. Although they are supposed to be daylight balanced, I find most of the time they are upwards around 6000-6500k... it will be rare that the bulb will actually be 5600k, and even then rare that multiple HMI's will be the same. I know some gaffers who will go to the lighting/grip rental house days before a shoot and test each HMI for this reason. They usually only take the heads they want from the rental house, which are heads that either match each other or are 5600k. Since you may not get that luxury, I'd have some small strengths of CTB, CTO, PlusGreen and MinusGreen on standby. If you don't have a color meter, this process becomes forsaken or incredibly difficult.
    4.5) I mention MinusGreen and PlusGreen, because as HMI's are not tungsten/carbon based lighting tools, they can have a color spike in 'tint' or the magenta/green spectrum. Some HMI's can give some nasty color spikes. Be prepared.
    5) There are two types of ballasts, both need to stay as dry as possible. Even in dry climates, or nice days, grips will put a small half apple box under a ballast to keep any water, dirt, and other things that may come in contact with the ballast on the ground, clear and dry. If using electronic ballasts in the bright outdoors, I like to have a small c-stand and a 2x3 solid to keep it in the shade and cool. Those things are little computers.
    6) When allocating power on home circuits or balancing loads on generators, remember that HMI's pull a very heavy initial load when starting up. Don't strike too many HMI's at the same time if they are on the same line. Most HMI's are 1.2k's and above, so if you are in a household, it's typically one per circuit... however many smaller HMI's exist, and you may have them. So if you have a 1.2k HMI and a 650 tungsten unit on a house circuit, don't be surprised if during power up, you trip the circuit. It would be better to make sure the 650 was off, strike the HMI and in a min or two, power on the 650w.
    7) HMI's are not dimmable in the sense you can intercept their power line with a hand squeezer or variac dimmer... You can't. If dimmable, they will have their own dimmer on the ballast. I've heard some of the very new HMI's don't do this, but from all the ones I've worked with, dimming an HMI does the opposite to color temperature as it does to tungsten units. The light will rise in color temperature as you dim the light down. Usually the dimmers on HMI ballasts don't have an incredible range, perhaps dimming a simple one stop difference.
    8) When you turn off an HMI, unless you strike it immediately, you will most likely need to wait a period of around 5 min for the unit to be able to re-strike.
    9) HMI's are not continuous lighting units. They illuminate a scene by very fast pulsating bursts of light. We cannot see this very well, but our cameras can. Only very specific frame-rates/shutter angles may be used on cameras before you start to see the flickering in your image. Look carefully, because sometimes it's hard to see on set when you have 1000 other things on your mind. If shooting with a magnetic ballast, your choices will be less than a flicker free electronic ballast, which despite the name, only offers a handfew more options before you still get that flicker. Don't worry though, people shot films for decades with standard magnetic ballasts and they did just fine! Most average shutter angles and frame-rates are safe.
    10) Keep what ever glass lens is on the light, on the light. Not only can HMI bulbs occasionally (very rare) explode upon death, but HMI's without the lens, gives harmful UV rays that can give your talent a tan and a headache. Don't open-eye the light.

    That's all I can think of.
    Last edited by Ryan Patrick O'Hara; 03-29-2011 at 03:02 PM.

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    Senior Member h-munster's Avatar
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    There are a lot of safety rules, and it would be tough to cover them all in this thread.

    First rule: the last item to remove from a stand (especially if it is supporting a heavy HMI) is the sand bag. People have been killed because an eager newbie pulled the bags before a stand was safely lowered, and a heavy fixture fell on someone's head. This rule goes double if the stand is on a balcony, in which case, there should probably also be a proper tag line rigged.

    Keep all stingers (extension cords) and cables neat, tidy and out of the way as much as possible, with all of the slack coiled up (in a clockwise wrap) near the light. "Clotheslines" are a definite no-no. Neatness can prevent tripping accidents, and neatly run cables can help quickly track-down and resolve any electrical emergency. Of course, things move quickly on set, and you might not have time right away for neatness, but there is usually time between takes to tidy things.

    Someone mentioned not to turn off an HMI, expecting to turn it right back on. This is especially true with older units that lack the hot-restrike feature. It is usually best to connect 50 feet of head cable (if possible) before striking an HMI. That way, the fixture can be be positioned within a larger area, avoiding the need to turn it off for repositioning.

    Always announce "striking" when turning on a ballasted fixture, and "light on!" when turning on other fixtures. If there are people in the area that is to be illuminated, aim the light away from people, and turn it on. Then, rotate the light into position.

    If you are working with an HMI that takes mountable lenses, always have a lens on before striking (unless otherwise instructed). The pin-point of the unlensed beam can be oppresively intense. Likewise, avoid changing lenses when someone is in the beam.

    Always close the latch over an inserted lens, and always latch the lens box when not in use.

    Be careful when reaching over the top of a hot light to change a scrim or lens -- it's easy to singe your forearm. Of course, a pair of leather gloves or set gloves helps in handling hot items.

    With any Fresnel fixture, have it focused to full spot before turning it on. The bulb is at its farthest distance from the lens at this setting, which can save the lens if the bulb bursts.

    If you are running heavy distro, connect in this order: ground (green), neutral (white), hots (blue, red, black). Disconnect in reverse order. Do not disconnect the white first -- you'll blow any 120 volt fixtures that are running.

    Don't try to be a hero when moving coils of heavy distro -- use a cart. Trust me, it's not worth ruining your back.

    If you have to run power up to a balcony or other high spot, carry the coiled cable up to the balcony and lower the plug-end down. People have had their teeth knocked out by the connector when trying to fling a cable end up to someone on a balcony.

    When moving a heavy light on a wheeled stand, point one leg forward in the direction of motion, and don't rush.

    Steel-toed footwear can prevent black-toe if you are moving heavy HMI ballasts, especially up and down stairs.

    Before lifting a heavy light onto a stand, lock the stand wheels and make sure that the knob on the stand's Junior pin receptical is fully loosened, so that the fixture's Junior pin can be fully inserted. The easiest/safest practice is for you and a buddy to first lift the light to the top of the stand, with the bottom of the fixture resting on the stand's Junior pin receiver. Then, count "1, 2, 3," and lift the fixture holding it by it's yoke and guide the pin into the receptical. Watch out for pinch points.

    When setting C-stands, remember the "righty-tighty" rule. Also, don't arm-out anything, when you can simply put the C-stand where the light control is needed. Not only is an avoidable arm-out considered "ugly rigging," but it is less stable (requiring sandbags), and it often creates an unnecessary "poke-point" with the bare end of the the grip-arm. For safety's sake, this poke-point needs to be covered with a tennis ball, go-ball, styrofoam cup, a hanging piece of bright tape, etc.

    When blackwrapping a light, try not to cover the fixture's vent holes. If you must cover the vent holes, try to leave space for the hot air to escape.
    Last edited by h-munster; 03-29-2011 at 02:30 PM.


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    Ryan and h-munster, these are two of the best posts ever.


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    Senior Member djkarn105's Avatar
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    Quote Originally Posted by Barry_Green View Post
    Ryan and h-munster, these are two of the best posts ever.
    agreed, thanks guys
    "Without the Chaos, there would be no happy accidents"


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    I think this should be sticky'd. This is great info for those that don't handle this kind of lighting daily.


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    Senior Member Jarrett P. Morgan's Avatar
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    Quote Originally Posted by Barry_Green View Post
    Ryan and h-munster, these are two of the best posts ever.
    Very much so!!
    Sticky worthy indeed.


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    I had been in your position before. What I did was, go to the Check Out. Learn how to use the light from the Rental House people, most of the time they are more than happy to show you the trick. You didn't mention about how big of a production, and I bet you won't go on a job with a 18k HMI, right. LOL
    In that case, I will just suggest some basic insights of running HMI.

    Arri, Desisti, LTM, Mole. They all make HMI.
    This is a normal HMI package.
    -HMI Head w/barn door
    Make sure you check that yok (the side handle that tighten the light), HMI head is heavy so from time to time it might be too lose or too tight.

    -Header Cable 25' (2x)
    Make sure you grab the right cable, some rental house color coded, some still have that Arri tag on. 575/1.2k (same cable), 1.2k/1.8k (same cable), 2.5k/4k share same header cable and such.
    Different company have different combo.

    -Ballast
    Same principal like the header cable. Sometime there is a switch for 575 or 1.2k (LTM ballast does). Read the labels, plug in the right hole. Make sure it is on flicker free and dimmer on 100%.
    Check the dimmer too, you don't want a broken dimmer button.

    -Lens Case and Scrim bag
    If you getting multi HMI, make sure you get multi cases of the same lens set.

    -Spare Bulb
    Must have. Learn how to open the lamp and put the bulb in safely. (Ask the Rental House to show you)


    For safety on set. A few things want to touch up on

    - I always turn on the switch on the head first and ballast last. If the bulb pop, it won't be next to my face. And it makes more electrical sense. You don't want the ballast already sending electricity to the head while the head is not on.

    - "Always close the latch over an inserted lens", for safety yes. But once the lamp get hot, the DP wants to change a wide lens or put a double in there. It will be a bitch to get that top latch to open back up. Often time, I just leave the top latch open. However, at the end of the day don't forget it is open, you don't want the lens roll out when you take the light off the stand.

    - Tie some slack header cable to that string at head so it doesn't create tension or banning the cable --> bad ---> heat, bad connection, arch --> fire

    -If you are using a spot lens, depend on lamp size, don't try to apply gel straight to the barn door, it will burn through. or apply with heatshield gel.

    - Get the lens case/ scrim bag next to the light. If you change lens, put the hot lens on top of the box to cold down and put it back in once it is cold.

    -Once you strike the light, do not touch the light till it is fully speed because it has a great chance to un-strike the light. Once it strike, don't turn it off if it is not necessary. If you need to move the light 10 feet, it is a two person job, one move the stand w/ the light on and the other one follow with header cable. Again, do not turn it off if it is not necessary and still can safely relocate the light.

    - Tell the Grip Dep. to get a ladder next to that HMI, it is a hot lamp, believe me you don't want to joke around.

    - RAIN, it is a sucker for rain, you need full protection. Cover the lamp, ballast (pancake under it), connection (pancake). Can't let them wet. Check the weather before you go on the job. Order a roll of Celotex.

    -Ballast will make some high frequency sounds that Sound Dep. will pick it up so if they happen to ask for solution. Build a sound blanket wall w/ c stands in front of the the ballast.

    -Wrapping, if possible, wrap stand, cable, ballast first and the head, lens last. They need time to cool down.
    If you ever dealing with 12k,18k, you should put a scrim in to help cool down easier and more evenly. Quick temperature drop will crack the lens.

    Agreed, Steel-toed footwear is a must, saw the BBE getting the 6k off the low shelf in the truck, got trip over, lamp landed on his toe. He was wearing a skater shoes. Didn't see him on again after that day.

    Last year summer I had an experience with a 6k ballast explode and last month a 6k bulb explode. It happens rarely but they do happen. Just be safe on set, and you will be fine.

    If you are seeking further knowledge about HMI
    There are s*%t load of info written by this guy name, Guy Holt.
    http://www.dvxuser.com/ht...enerators.html

    One more note, get a killer Best Boy Electric on your team to cover your ass is always the best option.

    Good Luck


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