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#1 Tim Robbing Banks

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Posted 22 January 2012 - 03:27 PM

On a project coming up, I will be shooting a film lit entirely from a single light source. In the film, there is no light on earth until the character discovers an orb of light, which he brings back to his village. I have been doing some camera tests with china balls, but my main problem is finding a fitting "orb" for the film. I have looked around, and have not really seen much of anything that would suit my needs. I need something that would preferably be around 6-10 inches, battery powered, and at least 100W. Any ideas?

Shooting 5D, Cinestyle. Screencap was taken from test footage shot at iso160, 50mm f/1.4 with the Technicolor LUT applied, but no CC.

Thelight.jpg
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#2 Phil Rhodes

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Posted 22 January 2012 - 06:33 PM

Battery powered? 100W at 12 volts is over 8 amps. It's unlikely you could find a battery that would give you more than minutes of runtime that would reasonably fit inside a ten-inch sphere.
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#3 M Joel W

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Posted 22 January 2012 - 07:38 PM

You might be looking at lead acid batteries because of their high c rating, but those are huge. Alkaline batteries have a terrible c rating (very low drain). I discovered this the expensive way.

I would use CFLs rather than tungsten bulbs for their efficiency and lack of heat. There are 75w 12v tungsten lights but even then... 6 amps.

You could get a few of these and switch them out: http://www.bhphotovi..._High_Draw.html

Normal Anton Bauer camera batteries might offer similar performance. You could rent them to save money. My guess is running 12v lights at 14.4v won't make them explode. I've been wrong before.

You could run 12 9v batteries in sequence to a 110w fluorescent light. With lithium batteries you probably can get some acceptable amperage, too. Warning, you could get shocked at a potentially lethal voltage? I'm not an electrician. Probably don't do this.

There's a video where someone runs a 220V fluorescent off a single AA alkaline battery by cannibalizing a fuji disposable camera circuit board.

I recently ran a tungsten balanced triphosphor 15w 12v CLF off 8 lithium batteries. I used the battery pack for a marantz sound recorder but similar battery packs are a few dollars, $20 for the batteries. Very lightweight and pretty small. 60w equivalent and about 1.25 amps each so with a lithium camera battery that can output 12 amps you'd have a very bright prop indeed. NihM batteries are rechargeable but I'm not sure they have a high enough c rating. Alkaline batteries do not! The bulb flickers a lot. Maybe I'll build a portable fire rig out of a bunch of these.

Getting a spherical diffuser that doesn't eat too much stop will be a challenge for your art department. There are spherical hard plastic soft boxes for some strobe lights. Look around!

Is this the only source in your entire movie? You might want to put a chinese lantern on a fishing pole at the very least and bounce some very soft fill when the light is on.

Edited by M Joel Wauhkonen, 22 January 2012 - 07:40 PM.

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#4 Ari Davidson

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Posted 22 January 2012 - 08:46 PM

If the light doesn't have to be white. You could try chemiluminesence (i.e. glow sticks). The cheap way to achieve this is fill an object with water and drop the guts of a new highlighter in it. Hit it with some UV light and it'll emit a sufficient glow.


100w untethered is a bit of a tall order...


Alternatively, a couple of strategically placed 3" Rosco Light Panels could illuminate a frosted acrylic orb of sorts.
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#5 Matt Read

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Posted 24 January 2012 - 01:40 PM

You might consider LED Christmas lights. I have a string of 50 that only uses 3 watts and produces no heat. You could connect a couple strings and hook it up to a battery and stuff the whole thing in whatever you find to use as an orb.

Edited by Matt Read, 24 January 2012 - 01:44 PM.

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#6 Mathew Rudenberg

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Posted 24 January 2012 - 06:37 PM

Sounds like a fun build. This is the route I would take:

Several 12v SLAB batteries (Sealed Lead Acid Battery). They're big and heavy but are also cheap and seem to last fairly well - you can buy replacement batteries for UPS power supplies in various sizes and strengths.

Then you want to find your maximum output for least power, LEDs are somewhat more efficient then CFL's so that might be a good route. You can buy 12v LED turn signals for cheap, or all kinds of LEDs for boats and cars.

The trick will be your globe construction. I assume you want a perfect sphere of light which means the battery will need to be inside the sphere. This means you need several sources around the battery so that you don't see the shadow of the battery.

You'll also need to be able to change to a fresh battery whenever it runs dry. I wouldn't go with the china ball - too delicate. I would try to find a plastic sphere that can be unscrewed into two parts, frost it, and create a support cradle for the battery to sit in the center out of transparent plastic.

For practical purposes I'd probably build at least two - one battery powered and one that could be plugged in. That way you won't have to worry about the battery running out when you're lighting or doing a shot where you could hide a cable.

Good luck!
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