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Not sure where to post....How many Watts do you need for Lighting Interview?

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Milton Hockman
Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 20, 2010 at 11:26:32 pm

I've seen people building their own softboxes. I want to do it for fun.

However, I don't know how man watts to put in the thing. I'd like to use CFL bulbs.

what's a good watt to put in that will give enough light for an interview and not blow the light circuit either?

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Cory Petkovsek
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 21, 2010 at 12:56:10 am

Definitely NOT in business and marketing. How about lighting design pros, or possibly corporate video?

I don't think your question is the right question, so I'll answer it in parts.

How much wattage for a lightbox?

Watts in tungsten gives a different luminance value than watts in fluorescent. Look at other softboxes and see how they are built by manufacturers. You need to make it big enough to dissipate the heat that your light puts out. I'd look at coollight's 200w bulbs or EIKO's 105w bulbs. I haven't used either; note the medium vs mogul base. I'd put as much wattage as you can put in it without it melting or burning.

http://www.coollights.biz/cl20056-cool-lights-200w-5600k-high-softbox-bulb-...
http://www.coollights.biz/cl20032-cool-lights-200w-3200k-high-softbox-bulb-...
http://www.amazon.com/COWBOYSTUDIO-Compact-Fluorescent-Daylight-Listed/dp/B...
http://www.amazon.com/CowboyStudio-Compact-Fluorescent-Daylight-Listed/dp/B...


How to light an interview?
One softbox isn't enough. Will you light both people? You probably need three light sources one or two being a softbox is fine. You'll want a bare minimum of 500w, 250w and 90/150w in tungsten. Even at these minimums it will take some ability to light well. Two 5-600w and a 150/250w hair light would be better for one person, or a 1k, 500w and a couple hair lights for two people. The more light you have, the easier it is to get a professional result. Divide by 4 for fluorescent wattages.

How many lights can a circuit handle?
Residences and older buildings have 15 amp circuits. Modern commercial buildings have 20amp circuits (denoted by an outlet with a horizontal slot http://en.wikipedia.org/wiki/File:Electrical_outlet_with_label.jpg).

Remember this formula: P=I*V (Power = Amperes * Volts). Since your lights are 120v, and a single circuit may be 15 amps, that gives you 1800 watts to use before flipping the breaker. Everything plugged in to a circuit will have an ampere draw written on the device. When plugging into a circuit, add up the amps of all devices to see if there is room for your lights. Use multiple circuits as necessary.

Cory

--
Cory Petkovsek
Corporate Video
http://www.CorporateVideoSD.com


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Mike Cohen
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 21, 2010 at 3:36:04 pm

I think Cory has explained everything nicely. If using CFL for lighting, be sure you know the color temperature, especially if you will be mixing with tungsten.

I bought a softlight a few years ago designed to work with incandescent or CFL. With the 100W CFL (something like 42W in CFL land) the output was pretty dismal.

I have seen on B+H some lights using 3 to 5 CFL bulbs - presumably the light output is ok from that. You do have the issue of safely transporting multiple CFL bulbs and spares in your light kit. And should a bulb break beware there is mercury in those. If you are in a public office building or school it is a real problem because it becomes a haz mat cleanup - schools have been evacuated for tiny amounts of mercury.

Mike Cohen


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Scott Sheriff
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 21, 2010 at 7:07:30 pm

Cory
"Remember this formula: P=I*V (Power = Amperes * Volts). Since your lights are 120v, and a single circuit may be 15 amps, that gives you 1800 watts to use before flipping the breaker. Everything plugged in to a circuit will have an ampere draw written on the device. When plugging into a circuit, add up the amps of all devices to see if there is room for your lights. Use multiple circuits as necessary."

Cory,
This is true, and not true. You can run circuits at their rated capacity, but only for a limited amount of time. Except for short term, or impulse loads like motor starts, you shouldn't put more than 70% of the breaker rating on a circuit. So for a 15A, that would be around 1200-1300W. If you run the full capacity, they will usually only last 5-10 minutes before they get hot and trip. On a 20A circuit you can often get away with a couple of 1K's, unless the breakers are in a spot that they can't shed heat easy, like a closet.
Also, it's pretty rare to get a solid 120V at the plug, its better to use 115V as a nominal 'real world' to calculate the load.
And of course this all assumes that there are not any other loads on the circuit.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Milton Hockman
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 1:10:11 am

how does this translate to CFL? if i use several CFL's that are equivalent to 1,000 watts, does it still draw the same amount of power?

Freelancer Designer Virginia - StephenHockman.com
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Cory Petkovsek
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 2:35:03 am

Every bulb: CFL, tungsten or non-compact fluorescent will have a wattage draw on it. "Equivalent to 1000w" is marketing for a similar light output of a 1000w tungsten bulb. You need to look at the actual wattage.

Wattage is a unit of power, not light. Lumens are units of light.

A 100w tungsten bulb and a 100w CFL bulb draw the same amount of power. The CFL bulb will output 4 times the light, thus may be marketed as a 400w equivalent bulb.

Power or lumens can be summed linearly. That is, 3 100w bulbs will draw 300watts. 5 3000 lumen bulbs will output about 15000 lumens. (Resistance for instance is not added linearly).

@Scott, thanks for the info on the breakers. I didn't know that!

Cory

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Cory Petkovsek
Corporate Video
http://www.CorporateVideoSD.com


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Scott Sheriff
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 8:00:10 pm

Cory,
National Electrical code actually says you can run 80% of a circuits rating for 3 hours. Check out 15A replacement duplex outlets, they are rated at 12A continuous, or check out that the biggest 115V space heater you can get is 1,400W, which is 12A
I like to figure 70% because no system is perfect, and I like to have some headroom to avoid tripped breakers.
Sometimes you just have to push the envelope, and put as much as you can on a circuit and shut off the lights between takes, but I think its better not to.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Scott Sheriff
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 8:01:06 pm

Cory,
National Electrical code actually says you can run 80% of a circuits rating for 3 hours. Check out 15A replacement duplex outlets, they are rated at 12A continuous, or check out that the biggest 115V space heater you can get is 1,400W, which is 12A
I like to figure 70% because no system is perfect, and I like to have some headroom to avoid tripped breakers.
Sometimes you just have to push the envelope, and put as much as you can on a circuit and shut off the lights between takes, but I think its better not to.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Scott Sheriff
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 3:11:05 am

"how does this translate to CFL? if i use several CFL's that are equivalent to 1,000 watts, does it still draw the same amount of power?"

So lets check out a really big commercial CFL, that I'm familiar with, that might work for what you want. A 150W CFL wide spectrum bulb like what is used in greenhouses. This is supposed to be equivalent to a 500W incandescent. So that would be 300W (2x150W) for a 1000W equivalent, if you want to use that as an example. That should be around 2.6A @115V. A Lowel DP with a 1K FEL lamp would be 8.7A @115V

The problem is the CFL is never as bright as they say it is in the real world. This 150W bulb is specs at 8,000 lumens. So two would give you 16,000 lumens. Compare that to an FEL which is a typical lamp found in a Lowel DP. That bulb puts out 27,000 lumens, at 1,000W. Over three times as much as the two big CFL's. So you really need four 150W CFL's using, and that is a little over 5A. Still less than the 8.7A an FEL draws.

I have a lot of experience with studio and field lighting, and owned a commercial greenhouse at one time, and have been around a lot of high wattage commercial lights including commercial CFL's, HID, Sodium and Merc Vapor, and my personal experience backs this up. I did some tests with these against the 1000W ballasted Metal Halide lights, and two of the 500W equivalents in fixtures that had similar reflectors, hung at the same height. The CFL's put out less than half the footcandles of the single 1K MH lamp. Watt for watt against studio Halogens, or straight tubes fluorescent like the Kino's, or commercial HID types and the CFL will always be last when you get out the light meter. So I would take whatever the CFL is supposed to be equivalent to, and double that if you expect to get the same amount of light as a Halogen.

Someone earlier mentioned the hazmat problem associated with mercury in the CFL, and that is with the relatively small home types. These large wattage CFL's are physical much larger, and could be a bigger problem if one broke on location. Thats not to say there isn't any liability with Halogens, but something to be aware of. I have heard of entire schools being evacuated because a janitor dropped a CFL while he was changing it.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Milton Hockman
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 1:14:48 am

BTW, i got this idea to build my own lights from NAB conference. Victor Milt had a CFL homemade lightbox that he promoted...says instructions are on his DVD "Light it Right" but i haven't bought it.

WHen i saw his softbox it had maybe 5 small CFLs in it.

Freelancer Designer Virginia - StephenHockman.com
Find out more about me, see my portfolio, and read my blog

Graphic Design Info, Web Page Tips, Video Production Guide BLOG
My blog updated weekly with industry tips, tricks, and news


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Mike Cohen
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 2:29:17 pm

Regarding safety - some shy away from Tungsten due to risk of fire from blown bulbs - of course you should always have a safety screen in any incandescent fixture. Back in college we had a lamp blow in a studio light - a shard of hot glass went right through a table and chair - luckily the news anchor had stepped away from the desk.

Once we were shooting an interview between a psychiatrist and a vet with PTSD - I warned them ahead of time of the possibility of a bulb blowing without warning - the danger there was perhaps worse than a fire!

To reiterate the need to know how much juice you are using - if you blow a circuit breaker in your house or office, that's ok. But if you blow a circuit in a commercial building, you may need a maintenance person to reset the breaker, and who knows what other devices are also plugged into that circuit. We were once in a medical clinic - 3 or 4 exam rooms and an office were all on the same circuit - not logical but not unexpected since a lot of older office buildings were not wired with modern electrical devices in mind.

Back to Milton's original question, and the details provided by the others - CFL is essentially a replacement for old fashioned filament glass bulbs for individual light fixtures. Although used in commercial spaces, using CFL bulbs in groups in place of higher output tungsten is questionable - not to mention the color temperature implications. But I guess the price is right.

LED, once the price comes down, will eventually cancel out CFL.

Mike Cohen

PS - While the lighting forum would be better, this discussion has to do with business also.


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Scott Sheriff
Re: Not sure where to post....How many Watts do you need for Lighting Interview?
on Sep 23, 2010 at 8:46:38 pm

Mike,
I agree fire, bulb explosion, and burns are real risks of using 'hot lights', especially on location. Always run a screen over an open fixture, and keep it away from drapes and furniture. They can get knocked over and burn carpets from residual heat in a second, even if the bulb gets knocked out, so use sandbags. They can also melt nearby plastic items, and set off fire sprinklers. Now that those non-contact thermometers have become reasonably priced, I have added one to my grip kit to check wall and ceiling temps around the lights.
Like a lot of professional tools, they should be respected, and not used by the untrained. Most of the time I hear about people having issues, is they got overwhelmed with the shoot, and weren't keeping tabs on the lights, or were just unaware of how hot they get over the course of a shoot.

You may be right about LED's. Seems like the price, and the narrow color temps are the big problem currently.

I think the problem with the CFL's is the curly shape isn't the most efficient for our use. As you said, they are really meant to replace incandescent lamps. They might be OK in a chinese lantern for area fill. But fixtures like Kino Flo's have a much better output per watt, and are more compact due to the straight tube shape, if you want a cool softbox.

Sure this discussion could be either Business, or Lighting. Fires and tripped breakers are bad for business.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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