LuxRender Textures Spectrum - LuxRender Wiki

# Colour and Spectrum

The colour of a light source or object depends on the wavelength of the light, or the combination of wavelengths at which a light source emits light. Although most light sources emit light at a continuous range of frequencies and our eyes are sensitive to a number of different frequencies, we still perceive the light as if it had a single frequency. This means multiple different spectral characteristics can result in the same colour sensation.

When light sources illuminate surfaces, the resulting perceived colour depends on the spectral distribution of both the light source and the surface. Because spectral characteristics can not be represented in an RGB image, LuxRender provides a number of additional ways to specify the spectrum of light sources.

## Blackbody

• Output value: color

### Description

By indicating a colour temperature, LuxRender will use the spectral distribution of a blackbody. This is useful for for example light bulbs (2800-3300K), candles (1850K) and the sun (5000-6500K). For a detailed explanation, see for example techmind.org

a range of colour temperatures. The middle lamp has a colour temperature of 6500K

## Equalenergy

• Output value: color

### Description

This spectrum emits light equally at all frequencies, resulting in white light.

## Frequency

• Output value: color

### Description

This experimental spectrum uses a sine wave. Its practical use is limited.

## Gaussian spectrum

• Output value: color

### Description

The Gaussian spectrum uses a Gaussian distribution. It is defined by a frequency (in nanometers) and the standard deviation of the bell curve. The latter controls the width of the curve; low values result in saturated colours while higher values result in less saturated tones. There is also an "energy" value which will determine how much of the incoming energy is reflected/transmitted/emitted.

So in a sense, this is a fancy HSV color selector, where wavelength = hue, width = saturation, and energy = value.

The Gaussian texture is generally the most useful spectrum texture for defining arbitrary light colors

lamps emitting light around 589nm, with increasingly wide spectrum

## Color Depth

• Output value: color

### Description

Color depth, also known as color at depth, is a texture designed to make setting absorption simpler. Normally, you set absorption by defining the color that will be absorbed, resulting in a color control that is essentially "backwards". This texture allows you to instead set the desired result color and how far the light should penetrate before reaching that color.

### Parameters

• Transmission color - The target color of the transmitted light as it reaches the defined depth
• Depth - The depth at which the specified transmission color is reached

## Regular Data

• Output value: color

### Description

This generates a spectrum using numerical data as input. A frequency range should be provided plus a number of values for emissions at regular frequency intervals within that range.

## Irregular Data

• Output value: color

### Description

This generates a spectrum using numerical data as input. A set of wavelengths and their respective emission power should be provided.

## Lampspectrum

• Output value: color

### Description

Lampspectrum uses presets to load measured spectral data for various kinds of lamps. You can find the whole set of lampspectra here and an older version

## Examples

The colour stripes are taken from the Gaussian wavelength (left to right): 380, 414, 448, 482, 516, 550, 584, 618, 652 and 686.

 Natural Daylight Paraffin Candle Flame SOX Low Pressure Sodium Discharge Lamp Regular High Brightness Blue LED Sylvania [G8T5 8W] Germicidal Lamp