by Olaf von Voss | 3rd August 2016
You probably know a lot about film lighting already. However, it might be a good idea to revitalize that dusty knowledge a little bit from time to time. Mark Vargo, ASC, is here to help. His video about the history and physics of film lighting may not be dew-fresh, but the concepts and physics are timeless, that’s for sure. The Concepts of Film Lighting The video you are about to watch is almost 3 years old but the concepts and the physics are still the same. LED sources and other technologies yet to come can’t alter the laws of nature, so don’t be afraid, dim the lights and watch this: Mark Vargo is definitely a pro in his field of work. He has an enormous list of credits on IMDB, ranging from VFX for the original Star Wars movies, to second unit DP for films like Rise of the Planet of the Apes. With such an amount of experience, wisdom is not far away, as you can see in the tip of the day section on his personal website: Don’t be fooled by thinking you have to shoot with only expensive movie equipment. Get with a handy friend and build a cheap slider or go to the hardware store and find a utility fixture to use as a light. Be creative in new ways! That is so true! But in order to be creative you’ve got to learn how to use your tools. And that includes some basic concepts and laws of physics. The Physics of Film Lighting One of the main concepts is about the spectrum of light which the human eye is actually able to see. The whole spectrum is divided in wavelengths, and only a very small part of this spectrum is visible to humans. On the lower end of the visible spectrum sits violet with a wavelength of about 400 nm, and on the opposite end you’ll find red with a wavelength of 680 nm. So, violet and blue have shorter wavelengths but these contain much more energy than the longer wavelengths represented by orange and red. spectrum of light – CC BY-SA 3.0 (https://commons.wikimedia.org/w/index.php?curid=2521356) That leads us to another vital concept of film lighting: color temperature. As we know, the wavelength of red is higher but it contains less energy, so a low color temperature (which is measured in degrees Kelvin) represents red and orange colours, while higher temperatures represent blue. That is important to understand because there are two major types of film lights available: HMI daylight sources (5600K) and tungsten sources (3200K). color temperature – credit: http://juliusngphotography.com/blog/wp-content/uploads/2011/03/Color-temperature-in-Kelvin.jpg A very important physical law related to light is the so-called inverse square law. It says: if you double the distance between light source and target you’ll end up with only a quarter of your original exposure. In other words, you’ll lose 2 stops. Also check out Richard’s post on getting exposure right for more information on this topic. reverse square law – by Borb, CC BY-SA 3.0 (https://commons.wikimedia.org/w/index.php?curid=3816716) Film Lighting Itself We’ve had a post about film lights before: Richards’s article deals with different types of fixtures and light sources. In order to understand the differences, the pros and cons, make sure to give it a read! In the end you will realise that there is no such thing as just one light that fits all situations. Each and every fixture, source or type of light has its reason to exist. You’ll have to master the craft of choosing the right one for the given job, and that takes a lot of learning and an even greater amount of experience. The good thing is, though, that unlike cameras which are brand new on one day and already outdated on the other, light itself won’t ever become outdated…Read more
by Richard Lackey | 16th February 2016
Often misunderstood, color temperature is an important concept which can have serious implications for the images which we create. In the picture above, you can see three versions of the same image—each shot with different in-camera white balance (color temperature) settings: Top left: incorrectly balanced at 3200K (tungsten) Top right: correctly balanced at 5600K (daylight) Bottom: final color correction, based on the properly balanced 5600K shot Looking at the example, it quickly becomes apparent just how important color temperature can be. Why is Color Temperature Important? It is vital to understand the ways in which color temperature affects our shots. Not only does it play a part in how white surfaces in our scenes are recorded, but it is also pivotal in the overall balance between every color of every surface in the scene. Usually, we want objects that appear white in reality to also appear white in our recorded images—and when white is balanced correctly, all other colors will be balanced correctly, too. A white surface appears white because your brain tells you that it is white. However, it may actually be reflecting the blue light of an overcast day, or the deep orange of the sun just before it disappears below the horizon. Camera White Balance While our eyes and brain adjust continually to changing light conditions, a camera will not. You have to tell your camera what color light is illuminating your scene, and it needs to be adjusted every time the light changes. This is your “white balance” or “color temperature” setting, and if you are recording any format other than RAW, this setting permanently determines the color balance of your recorded image. It is imperative to get this right as correcting mistakes in post can be tough. RAW If you are recording RAW sensor data, then your in-camera white balance setting only affects the way you are monitoring your image; it will be saved as metadata but will have no effect on the recorded image data. Recording in RAW gives you full control over the color temperature in post. Let’s start with a look at color. The Physics of Color Visible light is a form of electromagnetic radiation, with a frequency (wavelength) that determines its color. The frequency of light in the visible spectrum is between 390nm – 700nm (nanometers—billionths of a meter!). A red painted surface will absorb all wavelengths of light except the color red, red light is reflected, and our eyes detect the light which is registered by our brain as red. A white surface, however, is not selective: it reflects the full spectrum of wavelengths of any light falling on it equally. What is White Light? White light contains an equal mix of wavelengths (colors) of the full visible spectrum. This is why white light can be split by a prism into the different wavelengths it contains—white light is an equal mix of everything. It’s important to understand that every light source we encounter actually does have a color, it emits an uneven mix of wavelengths, and therefore “white” in our scene is determined by the color of light illuminating our scene. Color Temperature According to Wikipedia – The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. A black-body radiator is any object which fully absorbs all frequencies of light, just as a white body is any object which fully reflects all frequencies of light. Black-body radiation (according to Wikipedia) is the type of electromagnetic radiation (light) emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body. In other words, the hue (color or specific spectrum) of light emitted by a black body radiator is determined by its temperature. The sun or a tungsten incandescent filament lamp are both examples of near perfect black body radiators. The temperature of the black body radiator is measured in degrees Kelvin and therefore, the color (specific spectrum) of light emitted by a black body radiator can be determined by its temperature in degrees Kelvin. This can—and has been—mapped onto a chromaticity diagram, forming a curve called Planckian locus. Real-World Light Sources The below table is from Wikipedia and is a helpful reference for knowing the color of your typical light sources. Temperature Source 1,700 K Match flame, low-pressure sodium lamps (LPS/SOX) 1,850 K Candle flame, sunset/sunrise 2,400 K Standard Incandescent lamps 2,550 K Soft White Incandescent lamps 2,700 K “Soft White” compact fluorescent and LED lamps 3,000 K Warm White Compact fluorescent and LED lamps 3,200 K Studio lamps, photofloods, etc. 3,350 K Studio “CP” light 4,100–4,150 K Moonlight 5,000 K Horizon daylight 5,000 K Tubular fluorescent lamps or cool white/daylight compact fluorescent lamps (CFL) 5,500–6,000 K Vertical daylight, electronic flash 6,200 K Xenon short-arc lamp 6,500 K Daylight, Overcast 6,500–9,500 K LCD or CRT screen 15,000–27,000 K Clear blue poleward sky These temperatures are merely characteristic; considerable variation may be present. The easiest way to make sure your white balance is correct is simply to be aware of the light sources illuminating your scene. The two common standard color temperatures for film and video lighting are “Tungsten” at 3200K and “Daylight” at 5600K. Knowing those two numbers will go a long way to making sure your image is balanced for your light source within the ability to make finer correction in post. Keeping some other values from the table above in mind will also go a long way, for instance if it’s an overcast day outside, you may want to set your camera closer to 6500K. Planning Ahead Mixed light sources can often cause problems, and unless you are intentionally lighting with mixed sources for creative purposes, it is well worth keeping a single color light source in mind when planning ahead. A location recce goes a long way to determining how an area is lit during the day, at night, and what practical light sources are present. By planning ahead and identifying potentially problematic lighting conditions beforehand, you can make informed decisions about how to tackle lighting different locations and what equipment you will need. By understanding color temperature, you will always be ready to balance your camera even in situations where you have no control over lighting at all. Correctly setting your color temperature in-camera is easy. It’s definitely not something you want to fix in post, so always attempt to get your in-camera color temperature right and avoid the headaches that incorrectly balanced images can cause.Read more
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