Render Passes

Render passes are named differently in V-Ray and Arnold. In V-Ray they are called Render Elements (RE), and in Arnold they are referred to as an AOV (Arbitrary Output Variable). Below is a chart with V-Ray REs and their corresponding Arnold AOV.

V-Ray: Render Element	Arnold: AOV	Arnold: LPE
Lighting	diffuse_direct	C<RD>L
SSS	sss_direct	C<TD>L
GI	diffuse_indirect + sss_indirect	C[TD][DSVOB].*
Specular	specular_direct + coat_direct	C<RS>L
Reflection	specular_indirect + coat_indirect	C<RS>[DSVOB].*
AO: ExtraTex with V-RayDirt material	AO: custom AOV with Ambient Occlusion shader
zDepth (with near/far set to 0/1)	Z
Self-Illumination	emission	C[LO]
Diffuse	diffuse_albedo + sss_albedo	C[DV]A

The direct_diffuse and direct_sss AOVs can be further combined with the LPE C(<TD>|<RD>)L or more simply C[D]L.

All of the above LPEs can be output for a specific light group by appending the code <L.'light_group_name'> to them (replacing "light_group_name" with the name of the light group). For example C<RS><L.'Sun'> will give you the spec contribution for the light group named "Sun". Similarly, the reflections of a light group (indirect specular) are made by appending <L.'light_group_name'> after the asterisk on the LPE, for example: C<RS>[DSVOB].*<L.'Sun'>

Exposure and directional lights

The V-Ray implementation of a directional light multiplies the intensity by Pi. To get the equivalent light intensity in Arnold, set the exposure to 1.65. If you want the math for this the formula is log base 2 of intensity = exposure [ log₍₂₎ i=EV ] or inversely 2 ^exposure=intensity [ 2^EV=i ], therefore 2^1.6514=pi or log₍₂₎ pi=1.6514.

Normalize and spot, area, and point lights

The intensity of area, sphere and spot lights are the same in both Arnold & Vray, provided the "normalize" is disabled on the Arnold light. Having normalize off only works properly if the radius is non-zero, which needs to be set in the Arnold section for sphere and spot lights.

If normalize is enabled in Arnold, the shadow softness can be adjusted by changing the size (i.e., radius) of the light without affecting the light intensity, which can be an artistically intuitive workflow. When normalize is disabled, larger lights produce softer shadows and are brighter, which is physically correct behavior.

Shadow Softness

Shadow angle or radius determines the shadow softness. This must be set in the Arnold section of the light, as the ray-trace shadow section of the light has no effect.

Light Decay

Unlike in V-Ray, quadratic decay is enabled by default in the Arnold section of Maya point, spot, and area lights. The Maya decay dropdown which defaults to "none" has no effect. Decay is enabled by default on the parallel V-Ray Sphere and rect lights, but not on the Maya lights.