- The color quality is a result of the tubes only. ( The technology that makes the light is in the tube. )
- Modern high frequency electronic ballasts (which are very common now) do not flicker.
- There are many good choices of off-the-shelf tubes with the **CCI and a high *CRI.
- It is possible to "over-drive" off-the-shelf tubes with off-the-shelf ballasts to get higher output.
- Compact Fluorescent bulbs are a very promising technology for Ghetto-Flo lighting. They use electronic ballasts and have high output for their size and are available in the correct **CCI and CRI.
*CRI - Color Rendition Index. How continuous or "true" the spectrum from a light is on a scale of 1-100. 100 is perfect. Lights with a CRI over 85 are suitable for film and video. A CRI of 90 or better is great, but the light output of extremely high CRI lights is often lower than lights in the area of 85 CRI. Under 80 CRI is not good for film and video.
**CCI - Correlated Color Index A.K.A. "Color Temperature" - The theoretical black body color value of the light.
A quick survey of the available off-the-shelf hardware reveals that good home-brew flo lights can be built for significantly less than the cost of name brand flo-lights. (Anywhere from 1/20th the price to 1/6th the price, depending on various factors)
Intro:
The problem:
I needed new lights to replace my old photo light setup. The new lights had to meet certain requirements.
1. Must work for both still photography and film/HD/Video
2. Capable of producing soft light without taking up too much space.
3. Daylight balanced so they can be used in combination with natural light
4. As inexpensive as possible.
Kino-Flo (TM) and various other name brand manufacturers produce movie lights based on fluorescent tubes rather than tungsten or HMI bulbs. As you might expect, they emit a soft wrappy light similar to a soft box of the same size. Kino-Flo Tubes are available color balanced at 5500k (Daylight/HMI), 3200k (Pro-Tungsten) and 2800k (Consumer Tungsten). Kino tubes are engineered to have a good Color Rendition Index (high spectral continuity) and lack the typical green/blue spike many consumer and industrial fluorescent tubes have. Beyond the precision tubes, another "special" thing about Kino-Flos is the ballast. Kino ballasts are engineered to be flicker-free when shooting at normal motion picture frame rates.
For soft light, Kino-Flos kick are one of the finest solutions available. They have high output for the amount of power they use (nearly three times as efficient as Tungsten lights) and they hardly generate any heat. The problem is Kino-Flos cost too much. Even the tubes cost too much. ($20 each)
Would it be possible to build something equal in caliber for less money?
Theory:
I'd read that others had been experimenting with some of the (new-ish to the consumer market) electronic ballasts. In theory, almost any modern electronic ballast should be stable enough to be flicker free at regular film frame rates. While doing my research I noticed that there is now a commodity consumer market for "Continuous Spectrum" fluorescent tubes as well. In combination, these two consumer grade off-the-shelf technologies should be capable of producing a quite serviceable "Poor-Mans Flo" light. The name that seems to have caught on for this type of lighting instrument is Ghetto-Flo. From here forward I'll refer to them as either Ghetto-Flos, G-Flos or home-brew.
Testing Begins:
Though I've read a few accounts of peoples success building and using Ghetto-Flos, the accounts always seemed a little thin on details. Not a big problem really. But it did take me a while to gather all the information I needed. I tend to not really believe anything until I see it myself so I decided to do a series of tests to figure out my own "recipe". Considering that the bulk of the "technology" in a flo-light resides in the tube, the thing I was most interested in learning from my tests was what the quality of the light from various commercially available tubes looked like. Second, I was interested in the stability of the ballasts when shooting various shutter speeds/frame rates. Last but not least, I was interested in the total light output (LUX) from the ballast / tube combination.
While I attempted to be as methodical as possible my testing method is not highly scientific by any means. I do not have a color temperature meter or the equipment to accurately verify manufacturers published CRI, CCI or relative output of the various tubes I tested so I came up with a simple method to at least approximate the quality of each tube. I shoot a test scene with my digital camera in "RAW" and then color correct it for white balance in Photoshop RAW loader to determine it's approximate white point. I then color correct the same image to the stock "Daylight" and "Tungsten" white points to see, visually, how much the light color deviates from that white point. I do both tungsten and daylight because even though my current focus is daylight balanced tubes I may eventually test tungsten color balanced tubes. For the relative light output, I just use the exposure information from the EXIF data of the image which tells me if the light output is significantly different from one setup to another.
Here are the results from the tubes I've tested so far:
Recipes:
There are several recipes for home-brew flo lights. Here are a few I've investigated.
1. Use and off-the-shelf lamp housing with an electronic ballast + the correct flo tubes
2. Fabricate a lamp housing or modify one and use off-the-shelf electronic ballast (popular when over driving tubes)
3. Compact Fluorescent "bulbs" with reflectors and/or "China Balls"
Recipe #1 ingredients:
2 x GE Chroma 50 T12 48" [5000k, 90 CRI, 2200 LUX] ($3.50)
American Fluorescent Shop Lamp ($34)
Baby Plate ($4 used)
4 x #8 Screws ($?)
Total about $45 + TAX
The tubes I ultimately settled on where the GE Chroma 50 T12 48". They are inexpensive at only $3.50 each and available at Lowes and other hardware stores. Their CCI is 5000k with a CRI of 90 outputting 2200 LUX at stock power. The lamp housings I used were American Fluorescent electronic ballast shop lamps. They were the more expensive housings as far as shop lamps go, but I found them more attractive and ruggedly built than the really cheap lamps. It seemed like the extra few bucks were worth it. To attach the lamps to the C-Stand I screwed a "Baby Plate" to the top of each with short #8 sheet metal screws.
Recipe #2 ingredients:
4 x GE Chroma 50 T12 48" [5000k, 90 CRI, 2200 LUX] ($3.50)
Coroplast 1cm thickness
Aquarium VHO 4 lamp Electronic Ballast Kit + "German End Caps" (lamp plugs) And wiring ($160)
Velcro
Baby Plate ($4 used)
Clear Plastic Packing tape
Reflective Mylar Space Blanket ( $1.99)
3M "Super 77" Spray Glue
This recipe can be completed more economically by using multiple standard 4 lamp ballasts and wiring them to only 2 or even 1 lamp each. (Achieving an over-drive effect) Suitable electronic ballasts can be purchased for about 10 bucks each. The advantage of this scheme is that it allows running more or less lamps as required... A sort of poor-mans dimming. The "German End Caps" and handy because of the way they grip the tube, simplifying the mounting to the Coroplast with Velcro. Velcro is used to make tube removal easy. It's possible to remove the tubes and use them without the body/reflector.
Recipe 3:
Of these three recipes, the Compact Fluorescent is by far the easiest and most exciting. Since CFLs are self ballasted and all use electronic ballasts, 95% of you work is done by simply selecting the "bulb". CFLs also have incredibly high output for their size which is good if you are trying to get a "harder" light source. They'll never look like the sun or a Fresnel lamp, but you can at least get SOME shadows with a CFL in Par reflector. The only down side is that the best CFLs available seem to have a max of 85 CRI. It isn't a terrible CRI... but it is the minimum you should consider for film and video.
Research Continues:
Worth further investigation are the newer more efficient T8 and T5 tubes. In the end I didn't go with these because I was not able to find a local outlet for tubes of the correct specifications for a reasonable price. I went with T12s because they are common and inexpensive.
I've only just scratched the surface with over driving. It is an area that shows much promise.
Judging by their output vs. size, and how hot they seem to get I assume most CFLs MUST be "over driven" compared to regular tubes. Many of the commercial kits seem to use CFLs. I haven't even gotten close to exhausting the possibilities with Compact Fluorescents. There is currently a staggering selection of CFLs available with the correct CCI and CRI. It is worth further investigation.
