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light safety question


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#1 Jason Outenreath

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Posted 04 December 2007 - 10:00 PM

I'm shooting a scene in someones house. And I was wondering what the general safety limit for how many watts should go into any given outlet is, or how many for the whole house for that matter... I want to be safe about this, but I have some pretty ambitious lighting ideas. (its at night)

Also, I really want a lightening effect. All I have, is 3 arri open face 1k's, an arri fresnel 150w, an arri fresnel 300w, and two lowel omni lights. And assorted gels. I have a character that I want to reveal in front of a dark window with a flash of lightening. Would it work if I positioned two or all of the 1k's outside (at different angles) with full or half CTB, and connect them to a power strip so I can turn them on simultaneously, and flash it several times? Other ideas welcome. Or if this is impossible, please tell me. Thanks in advance!
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#2 David Mullen ASC

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Posted 04 December 2007 - 10:16 PM

This is basic electricity -- go to the fuse box and see how many amps each circuit is rated for. 20 amps is the most common, but some circuits are smaller, like 15 amps.

And remember that more than one outlet may share the same circuit, often the outlets along one wall. The best thing would be to switch off every circuit in the house except one, and then go around and plug a light into each outlet, and then mark the outlets that work under that single circuit. Then repeat for the next circuit.

Remember that items may be on in the house drawing power on that circuit, like the refrigerator.

Even though a 20 amp circuit can handle a little more than 2K, or 2000 watts, it's a good rule of thumb, 1 amp needed for every 100 watts. Or basically that you can't plug in more than 2K total into one 20 amp circuit, so you won't be able to put more than two 1K's on the same powerstrip and circuit. You could try three 650w lamps instead maybe.

The decay rate of the bulb generally means that switching a tungsten lamp off and on sort of looks a bit slow for a flash of lighting, though it may work OK.
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#3 Jason Outenreath

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Posted 04 December 2007 - 10:38 PM

Thanks so much! Could you offer any advice as to how to approach this lightening effect given my materials (or if you have ideas for how to eleminate the decay isssue with easy to find materials). What kind of key to fill ratio would I need to sell the effect? Or just generally, what can I use to sell it more effectively? Thanks.
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#4 Steve London

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Posted 05 December 2007 - 01:29 AM

Yes, on all the facts and advice regarding household current, thanks David.

Advice on lightning effects on the cheap is all over. Photographic strobes are often suggested but those who have tried them point out their extremely short duration is a problem plus it isn't easy to get a bunch of them and to to go off at once for cheap.

Haven't tried it but somebody with an electric arc welder is supposed to be able to produce a great effect.

I got a satisfactory result in a single window using a small but surprisingly bright 250W Lowel Pro light gelled full CTB. The filament has low enough mass that its rise and decay times looked good on video.

To get the stuttering flash effect that looks right you won't be able to use a plug strip and rocker switch. They're too slow and regular. We found that if you just partly plug the light cable into the stinger so that the circuit is not quite completed, you can quickly and irregularly rock the plug in the receptacle and get good looking flashes.

Don't try this with heavier lights or several lights because the higher current flow can draw a serious arc between the brass plug spades and receptacle contacts and besides being way too exciting for the crew doing the gag, it can burn and damage them. (I learned the hard way.)

As with anything like this, run some tests before the shoot. Tell us how it works out.
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#5 Jason Outenreath

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Posted 05 December 2007 - 01:40 AM

Yeah, I know that a lot has been said on lightening, but I was speaking to my specific situation with what I have... Which is not a lot. I find it hard to believe the lowel pro light was bright enough with full CTB for the effect. And don't there ahve to be more than one source for it to work and look right?
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#6 David Mullen ASC

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Posted 05 December 2007 - 01:43 AM

Well, I'd probably try and find a metal venetian blind-type shutter for the light -- usually these are large, made for big lights, but you could possible rig one to a c-stand and put a 1200w HMI PAR through it. Then manually slam the metal shutters open and close rapidly and randomly.

A bunch of old-fashioned flashcubes going off, slightly staggered, may also work but it would be very short in duration.

If the person isn't moving, it may be possible to create the flash effect in editing, by cutting in some overexposed frames of a lit-up face into a shot of a dark face.

The smaller lights may be bright enough if you can undercrank for longer shutter times and have the person move slower to compensate for the shorter frame rate.
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#7 Steve London

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Posted 05 December 2007 - 02:05 AM

Yeah, I know that a lot has been said on lightening, but I was speaking to my specific situation with what I have... Which is not a lot. I find it hard to believe the lowel pro light was bright enough with full CTB for the effect. And don't there ahve to be more than one source for it to work and look right?


It might have been 1/2 CTB.

Our shot had the camera on the interior. The room was dimly lit with a bedside practical as the motivation. The talent got out of bed and went to the window and looked out. The lightning flashes looked good.

The little Pro light was probably five feet from the window.
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#8 Hal Smith

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Posted 05 December 2007 - 08:57 AM

If you're the practical type: You could buy a set of passive louvers (no motor) intended for ventilation, paint them inside and out with Krylon #1602 Ultra Flat Black, rig a handle to them, and have a grip manually operate them in front of a 1kW (or so) lamp. http://www.grainger....ger/items/2C517 is a 10" louver for $16.50. A pair of HD C-stands should work for a mount. I've used this gag on stage in front of a Source Four, it should also work for film/video.
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#9 JD Hartman

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Posted 05 December 2007 - 08:59 AM

Could you just fire a photo strobe outside the window and capture that on film as a "placeholder", then add the lightning effect with editing software?
Lightning used to be simulated with a device based on a carbon arc torch. But it exposes the operator to possible burn from the molten carbon and short wave ultra-violet light.
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#10 Darrell Prohor

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Posted 12 December 2007 - 03:27 PM

A simple formula for determining how much can go on a single breaker in a residence is Amps times Volts equal Watts. In Canada most "normal" household circuits are 15 amps. on a 110/120 volt circuit. When calculating take the lower number. So 15 amps X 110 volts = 1650 watts. THIS is without anything else on the line. So you could plug in a 1K and a 650 but try to avoid having them on the same outlet as poor wiring will be at the outlet or (heaven forbid) at a junction box on the line. Also since the 80's electrical code states the fridge must be on a single line (breaker)
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#11 John Sprung

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Posted 12 December 2007 - 06:25 PM

This is probably the cheapest of all lightning effects, but it only works with film, not video: Just turn the camera off and back on again. As it slows down and comes back up to speed, you get some massively overexposed frames. Try brief flicks and longer ones, but remember there's no advantage in pausing with the camera stopped. The actor also has to hold fairly still during the "lightning". If you need sync sound after the flash, you'll need to tail slate. If you need multiple flashes with sync in between them, you'll have to eyeball it in post.




-- J.S.
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Visual Products

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rebotnix Technologies

Paralinx LLC

Opal

Technodolly

Abel Cine

Rig Wheels Passport