Continuous lighting questions

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Archive 2009 · Continuous lighting questions

Graham Mitchell
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p.1 #1 · Continuous lighting questions

I have to set up two large continuous lighting panels, around 150x200cm in size, for a special project.

It seems that I could do this in 2 ways:

- a bank of 6 foot long daylight fluorescent tubes behind a diffuser
- a single light source in a large softbox

1. Which option seems better to you and why?

2. Are any single sources likely to be brighter than a bank of 20 tubes 6 foot long?

3. Which light sources could I use in the softbox? What is the lifespan like?

4. Which of these options will give a more reliable colour response after white balance correction?

5. If I go for the tubes option I will probably have to make the bank myself.
What is the best tube to use? The best I found so far is the Activa 172: http://www.lightonenergy.co.uk/Daylight-T8-Tubes-p/t8-sli-activa.htm

Any other advice would be much appreciated!

Nov 07, 2009 at 10:34 AM

cgardner
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p.1 #2 · Continuous lighting questions

Film crews usually rent continuous lighting gear. Have you considered contacting companies catering to that market to see what is available on a rental basis?

It would be useful to know:
What are you lighting?
What shutter speed and f/stop do you want to shoot at?
How much space will you have?
How often will you need them?

Have you considered what a bank of 20- 6 foot tubes, ballasts, enclosures, etc. would weigh? Not to mention the crane needed to support it

Logistically a single source in a softbox or projected through a scrim would be simpler logistically but would present other problems like heat and the availability of sufficient power at the venue. Most locations aren't wired for banks of high wattage lighting. Learned that the hard way years ago trying to shoot wedding videos and blowing hotel ball room circuit breakers with the lighting

.

In terms of WB, tungsten sources can be balanced to neutral, but in to do it the camera must amplify the blue channel more than R and G, which also results in more noise in the blue channel and the overall image. The problem is worse at higher ISOs because there is more amplification of the signal the sensor records. Fluorescent lamps are have discontinuous spectrums with "tri-stimulus" peaks which correspond to the sensitivity of the human eye. Color Rendering Index (CRI) is a measure of how close they are to a well balanced full spectrum source. The higher the CRI the better. The specs for your lamps don't list CRI but 90+ is better for photo work.

Chuck

Nov 07, 2009 at 02:39 PM

PeterBerressem
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p.1 #3 · Continuous lighting questions

I'd go the fluorescent bank way. The Kinoflo charts may show the high efficiency of such a bank:
Kinoflo banks
A good tool for finding the equivalent HMI or quarz power is ARRI's calculator:
To achieve this power you'd need a lot of HMI in the box or behind a scrim, emitting excessive heat. Also the fluo bank will show a very evenly lit front panel.
Kinoflo's tubes have a high CRI > 95 as their Sylvania, GE pdf Phillips and Osram brethren as well. Practically no spectral difference to other continuous sources. When you build the banks you'll of course use high frequency ballasts to avoid any flicker.

Nov 07, 2009 at 02:45 PM

Graham Mitchell
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p.1 #4 · Continuous lighting questions

cgardner wrote:
Film crews usually rent continuous lighting gear. Have you considered contacting companies catering to that market to see what is available on a rental basis?

I am setting something up for a 5-year project. Rental is out of the question

cgardner wrote:
It would be useful to know:
What are you lighting?
What shutter speed and f/stop do you want to shoot at?
How much space will you have?
How often will you need them?

I am lighting something very unusual so for the sake of argument, let's assume I am lighting clothing on a manikin. The shutter speed is not important as the subject is stationary. The aperture will be f8. The studio will be chosen to fit the project, so compactness is a good thing but not at the expense of results. They will be is use 24/7 for an automated process taking around 7,000 eposures per day.

cgardner wrote:
Have you considered what a bank of 20- 6 foot tubes, ballasts, enclosures, etc. would weigh?

Yes but the lighting will never move.

cgardner wrote: The specs for your lamps don't list CRI but 90+ is better for photo work.

Yes, sorry about that. The listed lamp has a CRI of 98.

I have a feeling that the fluoro bank is what I need but I wanted some other opinions to make sure I hadn't missed something obvious

Nov 07, 2009 at 03:08 PM

Graham Mitchell
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p.1 #5 · Continuous lighting questions

PeterBerressem wrote:
I'd go the fluorescent bank way...

Thanks, I am beginning to feel more secure about this choice.

Nov 07, 2009 at 03:09 PM

cgardner
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p.1 #6 · Continuous lighting questions

Given the additional information lacking in your original posting I'd agree that it would be worth the investment in cost, time and logistics to use fluorescents.

You might want to start with a single part of lights / ballasts to get a baseline for output. You also might consider using 4' tubes running the other direction in the light box because it might be easier to obtain ready made 4' fixtures and find replacement 4' lamps. Another good color balanced lamp is the GE Chroma 50 - 5000K and high CRI. They have long been used in graphic arts as the standard for color viewing stations and light boxes. We equip our entire printing facility with them so lighting is color balanced everywhere.

Chuck

Nov 07, 2009 at 03:26 PM

jefferies1
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p.1 #7 · Continuous lighting questions

I did not think tubes put out a lot of light. You could build a ceramic socket on a frame and place 6-8 High watt, 5000K bulbs. Availailable from 105watt CFL (output equals 500 watts) to 200 watt and are cool overall ( base gets somewhat hot )
Cover with soft box covering. The light from CFL is soft to start with and does spread even with the swirl bulb designs. Nothing like a spotlight.
Look at below for bulb samples.
http://www.1000bulbs.com/2-to-200-Watt-Compact-Fluorescent-Screw-In-Light-Bulbs/

A large fan or two used for computer servers may be good for long use to keep air moving and cool in the enclosed area. Of course you would need a PC power supply box for power and suggest a couple A/C hookups to prevent circuit overload.

Nov 07, 2009 at 05:11 PM

Graham Mitchell
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p.1 #8 · Continuous lighting questions

Thanks again to all who replied!

Nov 07, 2009 at 06:45 PM


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