Bonus Lesson 2: Understanding Mixed Light Sources
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Bonus Lesson 2: Understanding Mixed Light Sources As you work in commercial photography you might have a huge variety of different assignments you may be asked to do and this will require you to have a variety of equipment, plenty of lights, and the ability to solve many photographic problems. Your business will depend on it. The difference with location lighting is that you now are lighting ‘scenes’ rather than just a person or an object. You will still light the person or object, but also need to light the scene around the subject and often this scene supports the subject. In some cases you may not be able to light the entire scene because it is too large and would require a significant amount of lights. This forces you to work in mixed lighting situations where the light sources within the building are a different color than your strobes. These two images are a good example. The interior of this manufacturing plant is lit with Sodium Vapor lights which cause the ambient yellow color cast when shooting with daylight film of white balance (WB). On the right is the same shot using the Auto White Balance feature of the digital camera. So if we have AWB why the fuss over color management in lighting? Consider your strobe lights. They are daylight and wont mix with the color of the available light. This lesson is about a variety of ways to deal with these mixed light sources and when to work with them or when to ignore them and how to combine your strobe lights with the ambient light sources. Ambient Light: Choosing TO USE it, but ignoring color shifts. There will be times when you need to see a whole area and do not have enough strobes to light the whole area or it is a situation where lighting it with strobes would not look real. Once you introduce ambient light into your photo, you risk a shift in color from that light and we will discuss that next. Here in these next few samples, we will look at using ambient light minimally so that it adds detail, but the color shift is not a problem. This image was shot for an auto body shop that was planning a large marketing campaign. The photo as you can see was in close and tight and not much background shows. Right behind the camera are windows and these are letting in some daylight, although not a lot and it is diffused. I placed an umbrella on camera right about 2:00 and another on camera left about 8:30. One more light on the floor is adding light and a reflection under the car and preventing a black hole. The fstop was f11 @ ¼ second and you can see that the ambient did not create any color shift. First, why do I need ambient light in this image anyway? If you guessed it was to capture to capture the sparks from the grinder you can take the rest of the day off. Sparks, fireworks, flames, and anything similar to this requires time to expose, so you have to pick a shutter speed that will do allow that. When you adjust to a longer S.S. to allow the sparks time to expose then you are allowing ambient light into your image and the result is often a color shift. In this image the window was brighter and thus was overriding the ceiling lights in brightness. So that is why there is no color shift. In this photo I again chose to allow the ambient light into the image capture but not correct for it. I had a portable strobe with small umbrella on camera right to light them in the face. This light overpowered the ambient and I also underexposed the ambient some. The color shift appears in back and in the jewelry case, but doesn’t really affect them. They look neutral for the most part but you can see a little amber on her blouse from the display case. Once again: If you choose to allow ambient light into your exposure and not color correct for it, you should expect a color shift in the scene. Once you add a strobe there are ways that you can minimize this shift without to much problem, but keep in mind it may not be suitable for every shoot. The way you do this is underexpose the background ambient light -1 stop and that means change the shutter speed. Let’s take this image of the couple above. You set up and take a camera meter reading and it says ¼ second @ f8. You take a picture and they are all yellow green from the ambient light shifting color-remember it is not daylight balanced. Sure you can use Auto White Balance (AWB) and problem solved, but that is not the answer here. Now you bring out the flash/strobe to light them quickly with one light in a Dine and Dash manner like above. You take another test and the daylight strobe light worked well and their faces look good, but the background is still pretty yellow green and so is the top of their heads. With your camera in manual mode, readjust the S.S. to 1/8 second. That is -1 stop S.S. from the pic above. Now the background ambient light has been cut in half. You take another test and you get the above shot; the people look pretty color corrected, and the background has plenty of detail even though it is underexposed -1 stop and its color shift is lessened as well. Here is one more image where I ignored the ambient color shift. I was also a Dine and Dash one-light job. It was a construction job site and in these hallways they hand strings of regular household bulbs in this chain of lights to light the hallways. Very tungsten orange! I set up my one light on camera left and took a test. I adjusted my fstop until the exposure on him was correct. The background was dark and I increased my S.S. until I liked how much of the background showed in the picture. The background was -1.3 from what the camera meter said was a good exposure. My choice to underexpose it minimized the color shift and made him brighter which makes him stand out. Ambient Light: Choosing TO USE IT and Correct for it. Ambient light sources could include lights that are tungsten, sodium or mercury vapor, fluorescent, and often there is a combination of more than one of these light sources at a location. They are rated in Kelvin Color Temperature with daylight being 5500K. Tungsten at 3200K is amber, sodium vapor are very orange/red around 2100K, and Metal Halide are closer to daylight. In these two images, you can see where the light was off color in the top image meaning it was shot using daylight white balance settings. Then in the lower image we corrected our strobes to match the ambient and then countered the color balance on the camera. More coming up! (3.1)Kelvin temperature color relationship: Amber warmer warm Daylight cool cooler blueish blue 3200K 3800K 4500K 5500K 6200k 6800 7500K 8000K There are different fluorescent lights, but the most common is Cool White. It has a Kelvin temperature around 4000K, warmer than daylight, but it also produces a green cast. Fluorescents not only need a correction for the blue/red shift, but need filtration to bring the green part of the spectrum into line. For the sake of explaining color theory, this lesson will illustrate points as if you were shooting with daylight film. I’ll address digital white balance later in this lesson. We will discuss first, how to filter for ambient light before we address adding strobes to a shoot setup. (3.2)The following is a color chart of light sources and their respective Kelvin temperature. Artificial Light sources: Candle Flame 1800K Sodium Vapor 2100K 40 Watt Bulb 2600K 75 Watt Bulb 2800K 100Watt Bulb 2900K 200 Watt Bulb 3000K Tungsten 3200K Mercury Vapor 3300K Photoflood Lamp 3400K Carbon Arc 5000K H.M.I. 5500K Daylight: Sunlight, sunrise or sunset 2800-3000K Sunlight; one hour after sunrise/sunset 3200-3400K Sunlight; two hours after sunrise/before sunset 3900-4100K Direct sunlight midday 5000-5500K Overcast sky 6000-8000K I usually do not correct for these natural outdoor color temperatures as I feel they add to the photograph. Warm sunset or sunrise light makes for a great photograph. In these examples you can see how the color shifts when using daylight film in non-daylight light sources. The left image goes orange/red in Sodium Vapor and the other image goes very green in cool white fluorescent lights. In both cases we are illustrating ambient light only, not strobe and both would require filtration on the camera to correct the color shifts for daylight film or be adjusted in the digital White Balance (WB). An example: Let’s say you go into an office to photograph a person. The first thing you need to do is determine what the color balance is before you even think about setting up your strobes. You do this by using a color temperature meter and I use the Minolta color meter (which unfortunately is no longer available because Sony bought Konia/Minolta). Once you have determined where you will be photographing and know that you will be mixing your daylight strobes with ambient, you take a color meter reading to determine what you will be dealing with.