Balancing Practicals to 5000-5600K

[Michael Hastings]

"Practical" is just a nickname for light fixtures that are seen on-camera, like a desk lamp, floor lamp, worklight, whatever. And these household and office fixtures use all sorts of bulbs, some are tungsten, some are fluorescent, etc. The fluorescent ones are generally easy to switch to daylight-balanced tubes.

You can switch ordinary tungsten lightbulbs to daylight compact flourescent bulbs, the main issue being how much green they have mixed into them, how good their CRI rating is.
http://en.wikipedia.org/wiki/Color_rendering_index

In terms of how high a wattage bulb you can put into a fixture, is just depends. Most plastic sockets say to not use anything higher than 60w in them, but how many people listen to that warning? You can put higher wattage bulbs in, but if you leave them on for too long, there is an overheating, melting, and fire hazard. I've used 250w "213" bulbs in ordinary table lamps, for example, but it does get hot. I've even managed to get away with 500w photofloods, but only for brief periods. If you are using a paper Chinese Lantern for lighting scenes, for example, it's a good idea to get rid of the ordinary plastic socket and get a porcelain socket from a hardware store, perhaps with a heavier gauge wire while you're at it.

One advantage to fluorescents, including compact flos, is that they are generally much lower in wattage compared to tungsten lightbulbs of the same brightness.

These EIKO bulbs were specifically designed for digital photography rated 93CRI:

http://www.eiko-ltd.com/Products.aspx?CatID=94&ProductIndex=SP30/955K

$13.90 at http://www.lightbulbemporium.com/eiko_48045ek_sp30_955k.asp
I have purchased from them.

Equivalent to about 75 watts normal household bulb:


Energy Used: 30Watts
Volts: 120Volts
Type: T4
Base: E26 Medium
CRI: 93
Length: 6.3"
Diameter: 2.76"
Light Output: 1,500 lumens
Average Lifetime: 10,000 hours
Color: 5500K
Beam Angle:
Filament:
Number in Case: 24 Unit(s)
Manufacturer
EiKO
Pricing Per Each Individual Unit
Price/Unit: $13.90

 

[Andrew Wilding]

Kubrick is using his hand over the bulb, playing his fingers as a moving cucaloris (handalouris).

Looked to me like he was holding some tracing paper over the bulb to diffuse it...

 

[Matt W.]

Yes, 60w to 75w. Think of it this way, the amount of blue gel needed to convert a tungsten light to daylight loses nearly two-stops of light. So half of 250w would be 125w, and half of that would be 62.5w... hence why the output is in the 60w to 75w range.

I hate to disagree with you because you're maybe the most technically knowledgeable and articulate person on this site (not to mention incredibly generous with your time), but I've found 250w 4800K photofloods to be highly efficient. I believe the filaments burn much hotter and closer to tungsten's 3700K melting point, which is why the bulbs last only four hours--and the hotter filament both produces substantially more light per watt and also increases color temperature, thus requiring a thinner blue dip. Also, certain blue coatings are more efficient than others; full dichroic glass filters are somewhat more efficient than CTB, for instance, and blue photofloods are only rated at 4800K.

Just to cite some specs on B&H, a 250w 4800K photoflood produces roughly 6000 lumens (likely a small exaggeration); I believe a frosted 100w light produces around 1600 lumens. Anecdotally, I've found these photofloods to be very bright and impressively close to their 3400K brethren. A normal 250w incandescent bulb in blue dip (2900K to 5600K) probably would produce about 1000 lumens, though, yeah, but I've never used blue dip so I don't know.

The other issue is these 250w bulbs get so hot that they're not really safe to put in standard fixtures, but that's not such a big issue, really, if you're careful. They do explode violently when water drops on them, though; I can confirm that.

As a rant to everyone else: Personally, I can't stand the idea of shooting a night interior with daylight-balanced fixtures. This is my amateur opinion but I've had some experience with this. I would consider the photofloods for day interiors, where the extra stop is necessary and 4800K looks nice and slightly warm against uncorrected daylight (and can be dimmed down to look warmer as needed). But photofloods are so bright they're hard to work with as practicals because they blow out whatever lampshade you put them under when shooting night interiors (unless you're just flooding your room with light), while CFLs are invariably green, and even HMIs do not have as nice a quality of light as true black body radiators. I have not tested this, but I believe metamerism would be a problem even with the correct white balance, which means skin tone rendering could look artificial and colors in general would not look quite right or expose quite the same. And 2900K is a beautiful light on skin tones because skin is so orange; HMIs are less kind to them and I believe David quoted a prominent DP as saying he found cool-whites (4100K) to produce extra contrast on skin tones, even when timed out. With the new color science, even ISO 500 footage looks very nice for night interiors to me, so I don't see the point of trading in pretty lighting for a small decrease in grain. If you exposure correctly, you're fine; if not, run it through NR.

Beyond this problem, balancing candles, lighters, or fireplaces (or any motivating source you can't replace with a photoflood or CFL) becomes impossible when shooting night exteriors balanced for daylight. You're dealing with a 1800K to 6000K discrepancy between flames and HMIs.

Lastly, re: china lanterns, I do not like the nylon ones although they're just about all I've used. They produce light that's fairly soft on the vertical axis but sharp on the horizontal axis (I do not know why); the advantage that they melt rather than catching fire really mitigates this problem, though, and they're pretty efficient... I worked with a DP once who really dug bucket lights (translucent five-gallon buckets with bulbs inside), but I didn't have time to build one before the shoot so I never tried it. But that's another potential china lantern replacement if you want a very even soft source maybe at the cost of light loss.

So that is my cranky, amateur opinion. No need to take it, but just some things to keep in mind.

 

[Matthew Rogers]

Is there an easy way to shoot a test with CFL's to see how their CRI is? In my mind, shooting them against white would be the best idea, but I'm not sure if the green will come out in the white like it will with skin.

Matthew

 

[Joe G.]

"Most all practicals one finds in homes now are tungsten bulbs and 4000k or so compact fluorescents (CFLS)."

I'm pretty sure that "most" CFL's in homes are about 2700K and very yellow.

I recently found some 3500K CFL's at Loews, and I'm happier with them. I haven't seen any 4000K CFL's yet. Where do you get them?

 

[Matt W.]

Is there an easy way to shoot a test with CFL's to see how their CRI is? In my mind, shooting them against white would be the best idea, but I'm not sure if the green will come out in the white like it will with skin.

Matthew

CRI is kind of an illusory concept, a single number intended to represent a broad phenomenon ("color rendering"), but most bulbs are labeled and that will give you a good estimate. Most 80+ CRI bulbs are tri-phosphor, which means nice color rendering but a green spike; kino flos have a mild green spike and wonderful color rendering.

The best instrument is a spectrometer, but in absence of that a color temperature meter will tell you color temperature and how much extra green, which you can then reduce using minus green gels. These are pretty accurate and cool little instruments.

Another trick is to take a cd and hold it up to the light source; the spectrum will be reflected back in it. If you see just a few colors and a big patch of green, that's a bad sign; if you see a smooth and even spectrum you know you've got good light. This is more useful than it sounds (though a really inexact science) and I encourage trying it out.

 

[Shawn Booth]

Eikos rule. $40+ a pop and large, but these guys rock

 

[Douglas Underdahl]

I've got some 85 watt Eikos that I use in my translucent umbrella China balls. Lots of daylight and not much power draw or heat. They're very large - I call them the Hitchcock size for the oversized props that he made for a bunch of his movies.

My Home Depot and Loews seem to have three or four categories of CFLs going from about 2800 to 5000 or so, with a nice display of actual lit bulbs so that you can compare. Have to try the CD trick - sounds like a good one. i'm far less inclined to use a color temp meter these days as I generally reference the monitor. Thats one of the really nice things about shooting digitally, rather than photo-chemically: instant playback.

Looks to me like Kubrick tried the 216 but then pushed it off to the side of his operator's chest, then used his hand instead. Probably it attenuated the light too much.

 

[cooper roberts]

Thanks for all the great info! Sorry for my noobness, trying to wrap my head around some of the basic physics and principles of all this. Ok, so say I'm shooting and an interior night scene and it's being lit mainly by a practical lamp (at about 3000k, right?) and maybe some moonlight coming in through the window. According to wiki moonllght is about 4100k.

So Matt W, in this scenario, you're saying it's a pet peeve of yours when you see the practical lamp using a cfl or blue photoflood (i.e. daylight temperature lamps)? Am I understanding that correctly? Why is that a problem exactly??

Ok, now say I wanted to add a little soft fill light to this night scene using a china ball. What bulb? Same kind as the practical light?

If the practical and china ball are around 3000k, how does the 4100 k moonlight factor into all this?

In Eyes Wide Shut a lot of the interior scenes are lit by practicals and window light. The light coming in from the windows is blueish (what lamps are they using for that? HMIs?) but the practicals are orangeish (tungstens?)...is that about right?

THANKS!

 

[cooper roberts]

God I feel like an idiot, but can someone clear up a basic premise for me. Sunlight is a high color temp, hence it's blueish/whitish. Why then do I feel that it sheds a yellowish/orangish light on its subjects? Do I have blinders on? Does this have anything to do with the nitrogen and oxygen in the atmosphere scattering the higher frequency blueish lights? Why does the moon, with a "warmer" color temp than the sun appear more blue?

 

[Erik Bien]

As another, higher-powered option for daylight practicals besides photofloods and CFLs, ALZO makes a medium-base 5300K HID with a remote ballast that accepts an Edison plug. The downside is they're very green and flickery for five or ten minutes after striking, and they also can't be dimmed or re-struck hot.

 

[Matt W.]

God I feel like an idiot, but can someone clear up a basic premise for me. Sunlight is a high color temp, hence it's blueish/whitish. Why then do I feel that it sheds a yellowish/orangish light on its subjects? Do I have blinders on? Does this have anything to do with the nitrogen and oxygen in the atmosphere scattering the higher frequency blueish lights? Why does the moon, with a "warmer" color temp than the sun appear more blue?

This is actually pretty complicated, but I'll explain the basics as best I can (and in a lot of detail since I have nothing better to do right now). Those in the know can correct me. I'm neither a scientist nor a professional filmmaker (and I'm a film school reject--as of this month) so this is just stuff I've read up on over the years. And keep in mind that what lights you use is a matter of experience and creative choice and none of the science behind it really matters at all if you can make your footage look good. If you want to learn how to light, go on set, go to school, or read a book. If you want some half-assed and unnecessarily confusing summary of wikipedia science, though, read on:

Visible light comes in all colors from red (750nm wavelength) to violet (390nm wavelength). Different sources output different colors of light, and most sources output a broad spectrum of wavelengths, a lot of different colors. If they didn't we wouldn't be able to see color. In some tunnels with sodium vapor lamps you can only see orange and black because those lamps emit only two orange wavelengths. The sun, however, emits every wavelength in the visible spectrum and so every color you see outside is, ultimately, from light originating from the sun and being bounced back into your eyes. Sunlight has a color temperature around 5600K, but it contains every visible color. (That's why adding a blue gel to tungsten to make it resemble daylight works; you're not adding any blue, but just subtracting orange.) I'll explain this later as I discuss the kinds of light we use:

The first kind of light source we deal with is the black body radiator. Black body radiators are materials heated to a certain temperature, which then output electromagnetic radiation, much of which is visible light. Tungsten lights are black body radiators; they are essentially just tungsten filaments heated to around 3000º Kelvin. (A degree Kelvin is the same as a degree Celsius except that the zero point is located at absolute zero (-273º C) rather than the freezing point of water.) Tungsten has the second highest melting point of any element, which is why it makes a good filament. Carbon arc lights are also black body radiators that burn at around 5500K. Although black body radiators generally emit every wavelength visible to humans, they emit most of their light around one wavelength and the rest kind of slopes off like a bell curve on either side. So tungsten sources emit their light surrounding a 3000K color temperature and carbon arcs surround a 5500K color temperature. The sun is a black body radiator, too (sort of), and it burns around 3500K--but the atmosphere works like a color gel and shifts this to between 1800K at dawn to 4800K at high noon to 8000K+ when it's cloudy. Lower color temperatures look red (1800K is red or about 750nm); higher ones look purple (12000K is purple or about 750nm wavelength) and in-between are orange (3200k), green (4100K), blue (5500K), etc. That doesn't mean the source emits only that color light, just that it emits most of its light centered at that color. So blue looks "cooler" but requires a hotter-burning radiator. (Astronomy relies on these principles; you can tell how big and hot a star is by virtue of its color temperature.)

Fluorescent lights work very differently. They are vacuum tubes full of vaporized mercury, which is then excited by electric pulses. When vaporized mercury is excited, the electrons in the mercury atoms jump between valence levels, and this produces specific wavelengths of light. So fluorescent lights don't produce a broad spectrum, like a black body radiator, but only a few wavelengths. To fix this, manufacturers coat fluorescent lights in phosphors, which are materials that glow (kind of like a black body radiator) when hit by a wavelength of light. By mixing phosphor coatings, light manufacturers can make fluorescent lights at any color temperature (well, between 2700K and 6500K, generally) and trade off efficiency (light output per watt) for color rendering quality ("CRI"). CRI is what percentage of visible wavelengths are output by a light source. The CRI of black body radiators is 100; fluorescents vary from 60 to 98+. CRI does not tell the whole story. Look at the wavelength of a black body radiator; it resembles a skewed bell curve. Fluorescent spectrographs are jumbled and often show a "green spike" or a disproportionate amount of green light. So a fluorescent light might have an effective color temperature of 3200K (kind of an "average" of all the wavelengths it outputs) and yet output way more green light than a tungsten lamp burning at 3200K, which is a true black body radiator. Yeah, it's kind of a mess.

The other kinds of lights we deal with are gas discharge lights (HMIs, street lights, etc.), which work a lot like fluorescents with excited mercury or sodium plasma (except that it's excited by an electric arc), which is mixed with other rare earth elements (which produce different wavelengths as electrons jump valence levels) to approximate a black body spectrum. These lights, like fluorescents, are highly efficient but often at the cost of color rendering. Sodium vapor lights are the most efficient gas discharge lamps but they only emit two wavelengths (around 600nm, orange). HMIs have fairly good color rendering but are expensive and require complex ballasts.

LEDs (I have no idea how these work) are extremely efficient but emit only one wavelength; this can be mitigated by coating them, like fluorescents, in phosphors, and by mixing various LEDs in an array.

So….that's light. You can also use gels, which block out some light and turn light to the color they look like; similarly, bounce cards that are warm will warm light up. Rosco has spectral emissions graphs on their gel website and wikipedia has spectrography for most sources so read up there if, for some reason, you're as interested in this as I am (my excuse: low-level OCD).

One last thing: your eyes adjust naturally to color temperature. So you can't use them to judge if things are warm or cool, except relative to each other.

As for why I don't like lighting interiors with daylight balanced sources, it's a due to a lot of things but mostly the fact that footage shot at 5600K white balance with daylight fixtures will not look identical to that shot at 3200K with tungsten fixtures because skin tones may be underexposed relative to blue with daylight sources and there may be slight color shifts due to a phenomenon called metamerism. The other reason is most daylight instruments are hard to control and have green spikes, which are also bad for skin tones.

 

[Joe G.]

Wow Matt. That was hardcore.

I think we need a wiki library for all this stuff.

 

[Isabelle Landers]

I've thought about the daylight CFL idea though for putting into Chinese Lanterns for a soft moonlight effect outside at night.

This post gives me an idea. I love the quality of Helium balloon lights but they are too expensive for anything but a feature budget. To create a poor mans version of a helium balloon I have thought about using a large paper china lantern (48”) and the 200 Watt 8u CFL bulbs pictured below in the fixture pictured below.

http://img.tradekey.com/images/uploadedimages/products/2/9/B476534-20070423031229.jpg

http://www.inspironphoto.com/index.php?main_page=popup_image&pID=51

With this fixture, I can cluster nine of the 200W CFL together and produce the tungsten equivalent of a 7650W Tungsten balloon. Since CFLs generate hardly any heat there is no fire hazard. The CFL bulbs will pull around 15 amps total so shouldn’t overload the fixture or a standard household circuit. For night exteriors I can lamp it with 5000K CFL bulbs and power it with a portable generator and still have enough power on the generator to run several small HMIs as well. Does anyone see any reason this setup wouldn't work?

Since this is getting off topic for this thread I have started a new thread titled CFL "Balloon Lights" at http://reduser.net/forum/showthread.php?p=562841#post562841. I will look for responses there.

- Isabelle Landers, Gaffer, Nashua, NH

 

[David Wyatt]

I don't suppose anyone has crammed daylight LED's into a lightbulb housing yet?

Hi David,

I haven't used these Philips bulbs myself but I spotted them a while ago and they stuck in my mind - they're not particularly powerful, but they are basically what you were wondering about - a set of LEDs crammed into a traditional ES bulb set-up (they're around 4200˚K - I'm not sure about CRI or green spikes etc - they're dimmable too which is handy). Incidentally they're probably the most beautifully designed light bulbs I've ever seen!!

http://www.litebulbs.co.uk/product/22560/philips-master-led-es-mv-bulb-cool-white.aspx

 

[Joe G.]

" Colour Rendering Index 70"

And at that price?

No way.

 

[Kyle Spicer]

Hi David,

I haven't used these Philips bulbs myself but I spotted them a while ago and they stuck in my mind - they're not particularly powerful, but they are basically what you were wondering about - a set of LEDs crammed into a traditional ES bulb set-up (they're around 4200˚K - I'm not sure about CRI or green spikes etc - they're dimmable too which is handy). Incidentally they're probably the most beautifully designed light bulbs I've ever seen!!

http://www.litebulbs.co.uk/product/22560/philips-master-led-es-mv-bulb-cool-white.aspx

I was just looking into this the other day and found these two links.

http://www.ledbulb.com/
http://www.ledcflbulbs.com/

Not suggesting to buy, or not to buy from these companies. I was just doing some research .