Limitaciones del estudio

Photometric

Lights

The Good…

Photometric lights in MAX are a double-edged sword. On one hand, they are the ultimate tool if you are going for a physically accurate recreation of a real-world lighting environment, especially if you need to use physi- cally correct luminaires in a physically correct environment. Nothing really matches the power and accuracy of these tools, so if you are an architect or a physicist, your prayers have been answered.

The Bad…

On the other hand, if you choose to use photometric lights, you’d better be sure that everything about your geometry is perfect. No light leaks are allowed, and scale must be exactly correct. Structures must be com- plete in detail; otherwise the lights will not behave correctly. So this means a great deal of extra work—not so good if you’re on a TV produc- tion deadline.

…and the Ugly

Perhaps the most unfortunate thing about photometric lights is that you are not supposed to use them together with standard lights. According to the documentation, they do not interact correctly and behave very dif- ferently. I have had some success mixing light types without too much trouble, but it is not really advisable to do this. You’ll have to try out the different combinations for yourself to see if they work for you. I have managed renders using standard, mental ray, and photometric lights together with expected results, so don’t forget to try!

If you are an artist more interested in look and effect than in physi- cal correctness, you’ll probably want to stick to standard and mental ray lights and leave the photometric lights to the engineers. But I cover photometric lights anyway because there are always some clever artists out there who have learned to make great use of unusual tools for TV and film production, so we certainly should not leave them out here. And of course, you might also be an engineer, architect, or physicist just dying for physically accurate lighting, so this chapter is for you.

Photometric Light Types

Just like standard lights, photometric lights come in free and target fla- vors. Instead of direct, spot, and omni lights, though, photometric lights come in point, linear, and area light types.

Point Lights

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Point lights behave much like standard omni lights in that they emit light from a single, nondimensional point in space. This is not a physically accurate model since all lights have some size; however, point lights render more quickly than linear or area lights because they are simpler to calculate.

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Figure 9.2: Point lights cause hard shadows because all the light emits from a single, nondimensional point in space.

Figure 9.3: You can soften the shadows of a point light by switching the shadow type to Area Shadows.

Note: The first time I saw target point lights, I wondered what the point of the target was. But targets can be very useful when you are orbiting or panning the light.

Area Lights

Area lights emit light over a rectangular area. You can set the height and width of the area in the Area Lights Parameters rollout. The area light is the most physically realistic of the three photometric light types, since real lights all have a height and width. In fact, real lights also have depth, making them three-dimensional. Area lights are two-dimensional, but that’s close enough for almost all lighting situations. The natural, raytraced shadows from area lights are the most realistic of all the photometric lights.

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Linear Lights

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Figure 9.5: This image was rendered with Advanced Raytraced shadows, not with Area Light shadows. The render takes longer than a point light with area shadows, but the shadow quality is much higher.

Figure 9.6: Notice in this image that a linear light is represented by a line, since that is the shape of the light source.

Linear lights are intended to reproduce light sources such as fluorescent tubes. The problem is that raytraced shadows from the linear light only soften along the length of the light, not along the width because…well, because there is no width to a linear light. Linear lights are one- dimensional, and therefore the shadows are only softened over one dimension.

IES Sky

“IES” refers to the Illuminating Engineering Society. Wherever you see these letters, it means a bunch of physicists have gotten very picky about the light behavior, and while you may not even notice the differ- ence or it might not seem to work the way you’d like, don’t worry—at least it’s physically accurate.

IES Sky is a photometric version of the skylight that you can use with Light Tracer to create outdoor fill light sources.

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Figure 9.7: Notice how the shadows seem to soften only in one direction, along the length of the linear light.

Don’t worry about the picky physicists, though. I have managed to get very nice-looking lighting from IES Sky without having a Ph.D. or M.Sc. Simply placing the skylight in your scene and dialing in the desired intensity by eye is usually going to be just fine, unless you are writing your doctoral thesis in wave theory or something.

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Figure 9.8: An IES skylight looks like a half dome with a target. It looks like a half dome because it represents the dome of skylight outside. The IES skylight, just like the standard skylight, can be placed anywhere in the scene.

IES Sky can also be used with IES Sun in the Daylight System discussed a little later in this chapter.

IES Sun

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Figure 9.9: Sure, it takes a little longer to render, but the beautiful results are worth it!

IES Sun is another photometrically accurate lighting instrument and is intended to be used with IES Sky for outdoor lighting environments. Once again, being the creative people we are, we certainly aren’t obliged to use the tools exactly as directed. I can throw an IES sunlight and an IES skylight together any time I want without using the Daylight Sys- tem and I will probably never be jailed for it.

Daylight System – Simulated Direct Sunlight Plus a

Photometric Skylight

The Daylight System can be accessed through Create>Lights from the main menu.

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Figure 9.11: An IES sunlight and an IES skylight interact to create an outdoor lighting environment.

Figure 9.12:

Accessing the Daylight System

Once the Daylight System is added to your scene, you will see a param- eters rollout that allows you to select the precise location you desire as well as the precise date and time of day. Unfortunately, if you don’t live in the United States, your city will not be listed in the Get Location list.

The Daylight System’s purpose is to provide physically accurate daylight models depending on your location on the globe and the time of day. This would likely be very useful if you were creating forensic anima- tions. If you’re an artist working in games or visual effects, though, you probably won’t have much use for the Daylight System.

For further details on how to set up and use the Daylight System, please see the manual.

Photometric Light Parameters

For details on photometric light parameters, please refer to Chapter 12, “General Light Parameters,” where they are covered in detail.

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Figure 9.13: Control Parameters rollout for the Daylight System

Photometric Light Presets

Here’s one particularly cool feature of photometric lights. There are a number of built-in light type presets. Say, for example, you want a 60-watt lightbulb, a halogen lamp, or a streetlight. You can fiddle around and try to find the right settings or, from the Create>Lights>Photomet- ric Lights>Presets menu, you can simply locate your preset, and bing! It’s in the scene.

Different light types come with different icons. All the settings are changeable in the Modify panel.

Exposure Control (Environment Control)

Exposure control can be accessed through the Environment and Effects panel.

This tool allows you to process the exposure of your image, just as though you were opening or closing the aperture on a camera. When using standard lights, you will probably not use this tool very often; however, when using photometric lights, the light energy calculations can be a little unpredictable and you may find the exposure control set- tings to be quite useful.

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There are a lot of details in the MAX documentation about how to use this tool, but it’s really quite easy to pick up if you just fiddle with it for a minute.

Keep in mind, though, that exposure control doesn’t have any effect over radiosity, so be sure you set your exposure before enabling

radiosity in your scene.

. . .

By now, you should have a basic understanding of the photometric light- ing tools available in MAX. In Part III of the book, we’ll be putting most of these tools through their paces to see what can be done with them.

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