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Photography Question 
Ellie 
 

tungsten vs fluorescent


Im reasonably new to artificial lighting in photography and was hoping someone could explain to me how tungsten light differs from fluorescent light?


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4/23/2006 3:07:11 PM

 
Pete H
BetterPhoto Member Since: 8/9/2005
  Hello Ellie,
Below is a link to color temps of various sources.

http://www.photo.net/learn/optics/edscott/cf000030.htm

The most basic explanation is the "color" of the light from these two sources is different.
Have ever seen a beam of light split by a prism?
This is called the "color spectrum" It is made up of light, both visible and invisible.
The human eye "sees" a VERY narrow part of this spectrum. At the upper end is Ultra Violet and at the lower is infra-red, neither which can be seen by the eye. Actually there are other types of light, but you will need to delve into some physics books on the nature of "radiation." :)

From a photographic point of view; and to answer your question more directly, Tungsten, sometimes referred to as "hot lights" because they emit heat, are skewed to the lower end of the light spectrum, hence they look "warmer" or more reddish without proper filtering.
One major drawback to tungsten is that they are not reliable over a period of time as their color will change as they age..and; variations in voltage will also change the color output.
Further; if you are photographing people, they are uncomfortable after a short time due to the heat they generate.

Fluorescent; is skewed towards the blue end of the spectrum, again, without proper filters, you get a "cool" or blue/green color cast to your photos. On the positive side, they are not hot as is tungsten.

Any light can be corrected to fall in the normal range of human vision, (White Balance), but for easing the workload, we try to find sources that are already close, such as flash or natural light that is closely balanced to what is referred to as "daylight" (approx 5600-5800K)
The "K" is simply the unit of measurement expressed in Degrees Kelvin.

Hope that helps a tad,

All the best,

Pete


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4/23/2006 7:50:55 PM

 
Bob Fately   Ellie, Pete's answer is pretty cmplete, though perhaps a bit misleading on one point.

Human vision, that is, what you and I see with our naked eyes, is the result of a bunch of biological systems and processes, from the retina to the occipital lobe of the brain. Because of all this "wetware", we unconsciously are able to "correct" our vision within a range of different lighting conditions. That is, if you see me wearing a blue shirt and yellow tie outside, and then we go into your home with traditional incandescent lights, you still perceive the tie as yellow and the shirt as blue. Likewise, if we step into a store with flourescent lighting, as far as you can see, my clothes still look the same, right?

Well, the physics of this is a bit different. First, remember that the color you see is based on two things - the inherent color of the object in question (the tie) and also the kind of light shining on it and reflecting off it to reach your eye. If I wear that same outfit under sodium vapro lamps, which are very yellow looking, you might see my shirt as almost black and my tie as almost white. THis is because the shirt fabric absorbs all colors except blue, and there is little or no blue in sodium vapor lighting, so nothing is eflected off the shirt. The tie, meanwhile, looks almost white in comparison because virtually all of the lighting from the bulbs reflects off it.

Now, machines, like cameras (and film), have no "wetware" to process images, they just record what's there. Most film is balanced (as it's called) for daylight on a clear day, which, as Pete stated, is about 5600K. (All that the Kelvin stuff means has to do with physics, too - it's the theoretical color of the radiation output of a black body heated to that temperature. 5600K is a lot, compared to, say, boiling water, which is 373K. As you heat a body more, the light becomes "whiter".

So, if you use film balanced for daylight, and take shots in your living room with tungsten light bulbs (either the common GE spherical thingies or halogen lamps), then subjects come out looking reddish or warm, because the light coming from those sources is 3400K or so; in essence, a redder light. So, you would use a particular filter (it's blue) to allow the film to render the colors the way you think of them. With a digital camera, you can set the so-called white balance to indoor or 3400, whatever; this accomplishes the same thing.

Flourescent lights come in a wide array of colors, usually bluish or greehish, but there are other flavors, and their a pain to deal with, but the basic physics is the same. The point is, though, that there is no single general color temperature for flourescent lights.

One final point - electronic flashes are made to mimic daylight (5600K); so no filter (or digital setting) is required when you use flash.


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4/23/2006 8:34:53 PM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  Could be simpler, without words like wetware. Because they produce light in different ways, they produce light with different wavelengths, so you get different color. Tungsten passes a current thru a wire, heats it up, produces light. Flourescent pass a current thru a gas, charges the atoms, they emit light when their electrons give off energy.


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4/23/2006 9:10:13 PM

 
Alan N. Marcus   Fluorescent lighting, introduced in 1938, became popular because of energy efficiency, about 80 lumens per watt with low heat generation. The tube contains mercury vapor. Electrodes at each end give off electrons that travel inside the tube. These electrons collide with the mercury atoms which when excited emit UV light. The inter walls of the tube are coated with fluorescent powders. These powders convert UV into visible frequencies. Various powder mixes produce different colors. The biggest shortcoming of fluorescent is a spectrum with peaks and spikes. This lamp typically imparts a greenish color cast. Perfect color correction is not possible as the spectrum is uneven.

Filament lamps date from the late eighteen hundreds. As electricity passes through the filament heat is generated and the filament glows to incandescence. Only 10 to 12% of the electricity results in light, the remainder generates heat. Tungsten has become the standard metal for the filament. Their spectrum is complete but shifted towards the warmest colors. During operation some of the tungsten evaporates. This spent tungsten migrates to the inside of the bulb envelope and blackens it. This backing blocks some of the light thus reducing output. Simultaneously, as the filament gets thinner and its electrical resistance increases causing the lamp to burn brighter and bluer. Thus the life cycle is brighter and bluer till burnout. A voltage change of 1 volt results in a color change of 10K. Voltage stabilizing transformers are required on color printers and desirable for studio lighting. The Quartz-Halogen bulb, introduced in 1959 was a major advance. The design eliminates blackening and helps evens out color and brightness during the life cycle by recalculating the vaporized tungsten back to the filament.

Photo grade lamps operate at 3200K - 3400K. Bluish filters can be used to produce a natural look. When measuring the color of light, both natural and artificial, scientist adopted the Kelvin temperature scale. This is the Celsius scale with a starting point of absolute zero. The idea was to create a scale devoid of negative temperatures. Absolute zero is the lowest possible temperature -273.16C. Additionally, the actual Kelvin temperature of a filament lamp corresponds quite closely. Think of a cannon ball with a hole in its side allowing you peer into a hollow center. Now heat this ball and watch through then hole as the temperature climbs. The inside of the ball starts to glow with incidence, first red, and then blue than white. Measure the balls temperature using the Kelvin scale and you have a unit of measure that links temperature to color.

Color films are available in different color balances. Natural daylight has an abundance of blue so daylight use film are balanced are made with a reduce sensitivity to blue. Daylight film is adjusted for 5500K. Films designed for tungsten applications require more blue sensitivity as tungsten light is deficient in blue. Tungsten type A film is balanced for 3400K and type B for 3200K.

Table of various sources:
Tungsten standard service bulb 2600 2800 K
Projector lamps 3200 K
Photoflood 3400 K
Flashbulb clear 4000 K
Electronic flash 5000 6000 K
Daylight 5500 K
Overcast daylight 7500 K
North sky no shadows 10,000 20,000 K

When color prints are desired, all modern photofinishing printers expose each frame on a custom basis adjusting the color and the quantity of the exposing light based on subject content. Most scene types are automatically color balanced during the printing cycle for a natural color. When automation fails, the printer operator can re-print with the preferred corrections. Generally this eliminates any need for color balancing filters applied to the camera. The same is true for digital photography as graphic software can neutralize most color balance errors.

When shooting color slide film and for those situations were exacting color balance is required, the photographer must pay close attention to detail. He has an arsenal of tools at this deposal, correction filters applied to the camera or the light source, a multiplicity of film types and/or digital setting plus corrections during printing or viewing.

When eating a watermelon, just spit out the seeds and keep on chomping.

Alan Marcus
ammarcus@earthlink.net


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4/24/2006 8:06:01 AM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Ellie,
The answers above are very informative, and for the most part, all correct. I bet they are also WAY more information than you were looking for. I'm an engineer and I've taken Physics classes on this stuff. While I understand it, as a photographer I don't really need to remember it all.

I'll take a more basic approach to answering your question. Tungsten lighting (standard light bulbs) can be used as artificial light in photography, but without correction, your images will have a warm orange tone to them. You can correct the problem by using Tungsten-balanced film OR a color-correcting filter OR if shooting digital, you can adjust your White Balance setting to the tungsten setting.

Fluorescent lights vary more in the color tone that will show up in your images. This makes it harder to correct for fluorescent lights. They also, in general, give very ugly results especially when photographing people. I would recommend avoiding the use of fluorescent lights in photography.


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4/24/2006 11:06:56 AM

 
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