More efficient sampling methods were developed to reduce the number of rays required to compute soft shadows from multiple lights. One example is an algorithm called ReSTIR, which calculates direct lighting from millions of lights and shadows with ray tracing at interactive frame rates.

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Shadow mapping has two steps. First, the scene is rendered from the light’s point of view into a special texture called the shadow map. Then, the shadow map is used to test whether surfaces visible on the screen are also visible from the light’s point of view. Shadow maps come with many limitations and artifacts, and quickly become expensive as the number of lights in the scene increases.

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As a result, real-time graphics solutions for global illumination are typically limited to computing a subset of the indirect light — commonly for surfaces with diffuse (aka matte) materials.

In most cases, ambient light is shadowed by a function of geometry around the surface called ambient occlusion, which helps increase the image realism.

The sun shines onto the lake and the trees, making the water look like it’s shimmering and the leaves appear bright green. That’s direct lighting. And though the trees cast shadows, sunlight still bounces off the ground and other trees, casting light on the shady area around you. That’s indirect lighting.

The UVFL is a battery-powered, handheld UV lamp that delivers high-intensity 1W/cm² irradiation at a 2-inch distance over a 3mm x 3mm area using a 40W UV LED. It is the most powerful battery-powered handheld UV lamp on the market. The UVFL features a specially designed UV collimating lens that maximizes intensity and homogeneity. With an internal cooling fan, It has a long operation time of up to 6 hours on its high-capacity 18AH 25V rechargeable battery. The battery is exchangeable so that one can purchase two batteries to continue the work while another battery is charging. The design leverages multi-year military UV gear developments, resulting in a ruggedized manufacturing tool for the mass market. The UVFL UV lamp is ideal for fast and deep epoxy curing, with continuous operation on a single battery charge, homogeneous illumination, lightweight construction, and ease of use. The lamp can be switched on and off with a finger-press button switch. An optional pluggable power supply and controller allow for hands-free operation with a foot switch pedal. The controller features a timer with settings from 0.01 to 10 hours, and the illumination power is adjustable from 10% to 99%. We offer three wavelengths ‒ 365nm, 405nm, and 440nm ‒ optimized for specific UV epoxy and paint curing applications. Additionally, we produce optical power meters that fit the head size to accurately measure and calibrate the power level.

For computer graphics to immerse viewers in photorealistic environments, it’s important to accurately simulate the behavior of light to achieve the proper balance of direct and indirect lighting.

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For indirect lighting and global illumination, even more methods exist. The most straightforward is called path tracing, where random light paths are simulated for each visible surface. Some of these paths reach lights and contribute to the finished scene, while others do not.

Using a complete simulation of lighting effects with ray tracing also means that the rendered images can contain some noise. Clearing that noise, or “denoising,” is another area of active research.

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Until the introduction of NVIDIA RTX technology, ray tracing was too costly to use when computing shadows. Ray tracing is a method of rendering in graphics that simulates the physical behavior of light. Tracing the rays from a surface on the screen to a light allows for the computation of shadows, but this can be challenging if the light comes from one point. And ray-traced shadows can quickly get expensive if there are many lights in the scene.

Many algorithms can be used for computing direct lighting, all of which have strengths and weaknesses. For example, if the scene has a single light and no shadows, direct illumination is trivial to compute, but it won’t look very realistic. On the other hand, when a scene has multiple light sources, processing them all for each surface can become expensive.

One way indirect lighting has been used in many video games is through omnipresent ambient light. This type of light can be constant, or vary spatially over light probes arranged in a grid pattern. It can also be rendered into a texture that is wrapped around static objects in a scene — this method is known as a “light map.”

ReSTIR dramatically expands the possibilities of artists to use multiple lights in games. Its newer variant, ReSTIR GI, applies the same ideas toward global illumination, enabling path tracing with more bounces and fewer approximations. It can also render less noisy images faster. And more algorithms are being developed to make path tracing faster and more accessible.

Direct lighting provides the basic appearance of realism, and indirect lighting makes scenes look richer and more natural.

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More technologies are being developed to help games effectively denoise lighting in complex, highly detailed scenes with lots of motion at real-time frame rates. This challenge is being approached from two ends: advanced sampling algorithms that generate less noise and advanced denoisers that can handle increasingly difficult situations.

Accurately simulating all types of indirect light is extremely difficult, especially if the scene includes complex materials such as glass, water and shiny metals — or if the scene has scattering in clouds, smoke, fog or other elements known as volumetric media.

Stencil shadow volumes are based on extruding scene geometry away from the light, and rendering that extruded geometry into the stencil buffer. The contents of the stencil buffer are then used to determine if a given surface on the screen is in shadow or not. Stencil shadows are always sharp, unnaturally so, but they don’t suffer from common shadow map problems.

It determines the color and quantity of light that reaches a surface from a light source, but ignores all light that may arrive at the surface from any other sources, such as after reflection or refraction. Direct lighting also determines the amount of the light that’s absorbed and reflected by the surface itself.

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Light bouncing off a surface, illuminating other objects is called indirect lighting. It arrives at surfaces from everything except light sources. In other words, indirect lighting determines the color and quantity of all other light that arrives at a surface. Most commonly, indirect light is reflected from one surface onto other surfaces.

Direct and indirect lighting has been present, in some form, in almost every 3D game since the 1990s. Below are some milestones of how lighting has been implemented in popular titles:

To tackle these issues, optimized algorithms and shading techniques were developed, such as deferred or clustered shading. These algorithms reduce the number of surface and light interactions to be computed.

Global illumination is the process of computing the color and quantity of all light — both direct and indirect — that is on visible surfaces in a scene.

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Indirect lighting generally tends to be more difficult and expensive to compute than direct lighting. This is because there is a substantially larger number of paths that light can take between the light emitter and the observer.

Path tracing is the most accurate method capable of producing results that fully represent lighting in a scene, matching the accuracy of mathematical models for materials and lights. Path tracing can be very expensive to compute, but it’s considered the “holy grail” of real-time graphics.