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# V-Ray Rect Light

## Introduction

• This lesson will take you through creating a rect light in V-Ray for Maya
• Also known as Rectangle Light/Area Light
• The information centers around the use of the VRayLightRect
• This lesson topic is approximately 30 minutes in length
• Lesson covers all 3 Learning Cycles for the Lesson Topic – Lecture, Demonstration, and Activity.
• Learning Outcomes: You will be able to light a scene with a VrayLightRect and understand how to adjust the settings for creating the look you want in your renders

## Overview

Goal - Develop the look for our miniature house set, to create something that has a cinematic feel.

Objective - We will light a scene with the VrayLight and understand how to get the desired results.

Outcome - You will be able to adjust the VRayLightRect to create different cinematic looks to your renders.

## Lecture

### 1. Terminology

Lighting is important to our lives and scenes in 3D. Without it we can’t see anything!

• Intensity - How strong the light will be in the scene
• Color Temperature - A real-world measurement of the hue of a light
• Shadows - Not just where the monsters hide! Can be turned off in 3D
• Sampling - The quality and physical accuracy of a light

### 2. Light!

a) Lighting in the real world

• Controlling the direction of a light
• Larger lights will have softer (more diffused) shadows

b) Light Falloff

Real lights have Decay. Light falls off to the square of it’s distance – Inverse Square Law

• An object at 2x the distance away from a light will receive 1/4x of the light it would at 1x distance
• An object at 3x the distance away from a light will received 1/9x of the light it would at 1x the distance

c) Light Temperature

Use the temperature value to create the right mood for your scene

### 3. Rect Light

a) Light Overview

• Intensity is the overall strength of a light
• The Units used affect if the amount of light emitted by the V-Ray light depends on its size

• U Size and V Size - Its preferable to adjust the U and V Sizes over scaling the light up and down
• Subdivs - Quality of the soft shadows created by the light
• Color vs. Temperature - Similar results but very different ways to get there
• Skylight portal - Ignores Color and Multiplier parameters – gets intensity from the environment behind it

b) Intensity, Color, Temperature

• Mode: Color - the light’s color is directly specified by the Color value. When using photometric units, this color is normalized so that only the color hue is used.
• Mode: Temperature - specifies the light color temperature in degrees Kelvin
• Great for matching real world lights
• Intensity Multiplier - defines the intensity of the light in terms of the units chosen in the Units parameter.

Color Mode: Color(with green Light Color)

Color Mode: Temperature (with Temp. approx. 2800-3200)

c) Units

Allows you to choose the light units. Using correct units is essential when you are using the VRayPhysicalCamera. The light will automatically take the scene units scale into consideration to produce the correct result for the scale you are working with. The possible values are:

• Default (image) - the color and multiplier attributes of the light directly determine the visible color of the light.
• Lumious power (lm) - total emitted visible light power measured in lumens. When this setting is used, the intensity of the light does not depend on its size. A typical 100W electric bulb emits about 1500 lumens of light.
• Luminance (lm/m²/sr) - visible light surface power measured in lumens per square meter per steradian. When this setting is used, the intensity of the light depends on its size.
• Radiant power (W) - total emitted visible light power measured in watts. When using this setting, the intensity of the light does not depend on its size. This is not the same as the electric power consumed by a light bulb. A typical 100W light bulb only emits between 2 and 3 watts as visible light.
• Radiance (W/m²/sr) - visible light surface power measured in watts per square meter per steradian. When this setting is used, the intensity of the light depends on its size.

d) Size
• Best to use U Size and V Size to adjust size of the Rect light
• The larger the light, the more diffuse the light and the softer the shadows

• Shadow Color - controls the color of shadows for this light
• Note that anything different from black is not physically correct

f) Texture

• Use Rect Tex - tells the light to use a texture for the light surface. If there are surfaces which are close to a texture-mapped light, it is best to have GI enabled. This allows V-Ray to use combined direct and indirect sampling for the light, reducing the noise for surfaces close to the light.
• Multiply By The Light Color - when enabled the colors in the texture are multiplied by the color in the Light Color parameter
• Rect Tex - specifies the texture to use
• Show in viewport - controls whether and how the texture is seen in the viewport
• Disabled - the texture is not displayed
• Texture only - the texture is displayed as it is
• Texture*Intensity - the texture is multiplied by the light intensity before it's displayed

g) Sampling
• Subdivs – controls the number of samples V-Ray takes to compute lighting
• Lower values mean more noisy renders, but will render faster
• Higher values produce smoother results but take more time to finish
• The actual number of samples also depends on the DMC Sampler settings
• Light cutoff threshold – specifies a threshold for the light intensity, below which the light will not be computed
• Useful in scene with lots of lights, and you want to limit the effect of the lights to a distance around them
• Larger values cut away more from the light; lower makes range longer
• Override motion blur samples – allows you to override the default number of samples that will be used to sample the current light for motion blur
• Motion blur samples – the new sample amount used to calculate when Override motion blur samples is turned On

Subdivs of 8

Subdivs of 1

h) Options
• No decay – light intensity is inversely proportional to the square of the distance from the light (objects farther from light are darker). This option removes that property making the intensity consistent forever
• Double Sided – controls whether the light is beamed from both sides of the plane
• Invisible – controls whether the rectLight source itself is visible in renders
• Skylight Portal – when On, the Color and Multiplier parameters are ignored and the light will take its intensity from the environment behind it

## Conclusion

a) Rect Light

• Intensity, Color, Temperature

b) Subdivs

c) Textures

d) Options

• No decay
• Double sided
• Invisible
• Skylight portal

## Demonstration

Time to see it work!

Watch while I demonstrate how to create and adjust a Rect Light in our miniature house scene.

## Activity

Time to do it yourself!

Use the provided start scene file to recreate the cinematic look as you have seen me demonstrate.
We have also provided a final scene for your reference.