AGi32 Roadway Luminance Calculations With Reflective Surfaces

This topic outlines the procedure and calculation methodology used to consider reflective surfaces in roadway luminance calculations. The primary application of this methodology is tunnel lighting, although it may be applied to other circumstances as well, such as overpasses and signage.

The calculation methodology uses techniques outlined in the IES Recommended Practice for Tunnel Lighting, RP-22-11. The calculations are limited to straight sections of tunnel only and do not consider daylight at this time.

Calculation Method Application

When Full Radiosity Method is enabled, reflective surfaces are considered as reflectors and obstructions. (See specifics below.) When Direct-Only Method is enabled, reflective surfaces are considered as obstructions only; they do not reflect light (only the direct component is used).

Environment Components:

Roadway Pavement Surface (RPS):

Roadway Contributing Surface (RCS):

Non-Roadway Surface Types:

Surface Types, Calculation Types, and Roadway Grids:

The following table summarizes the participation of AGi32's various surface types in roadway calculations.

Surface Type Calculation Type Included in Calculation of:
Model Roadway Grids
10 - Single Sided Direct Only Obstructive Obstructive
Radiosity Obstructive / Reflective Obstructive
11 - Double Sided Direct Only Obstructive Obstructive
Radiosity Obstructive / Reflective / Transmissive Obstructive
14 - Glass Direct Only Obstructive ** Obstructive **
Radiosity Transmissive Obstructive **
20 - Daylight Transition Glass (Transparent) Direct Only Obstructive ** Obstructive **
Radiosity Obstructive / Reflective / Transmissive Obstructive **
21 - Daylight Transition Glass (Diffuse) Direct Only Obstructive Obstructive
Radiosity Obstructive / Reflective / Transmissive Obstructive
22 - Daylight Transition Opening Direct Only Obstructive Obstructive
Radiosity Transmissive Obstructive
40 - Roadway Pavement (DFO) Direct Only Obstructive Obstructive
Radiosity Obstructive / Reflective Obstructive / Reflective
41 - Roadway Contributor Direct Only Obstructive Obstructive
Radiosity Obstructive / Reflective Obstructive / Reflective (direct component only)
Surface Opening (cut opening with no insert) Direct Only Obstructive *** Obstructive ***
Radiosity Transmissive Obstructive ***

 

* Cannot consider daylight with Roadway Calculations

** Obstructive if inserted into an opening, ignored if standalone

*** Surface openings are NOT consider in Direct Only or Roadway Calcs (i.e. considered obstructive)

 

Environment Construction:

Calculation Process:

Step 1: Calculating direct component:

Steps 2 & 3: Calculating indirect component:

In the second step (Radiosity), the Roadway Pavement Surface reflects the direct light received to the Roadway Contributing Surfaces. The Roadway Contributing Surfaces reflect light to other RCSs, but not to the RPS.

Obstructions from Roadway Contributing Surface to Roadway Pavement Surface are considered, as are obstructions from Roadway Pavement Surface to Observer.

In the third step, all surfaces are assumed to be double-sided; however in Render Mode, Roadway Contributing and Roadway Pavement surfaces are single-sided. In this step, RCSs reflect light to the RPS as follows:

Formulas:

I’ = Lo * Ao

Where:

Lo = Zone luminance = Exitance / p (Lambertian reflection is assumed.)

Ao = Zone size in m2

Id  = I’ * Cos(d)

Cos(d) = Cosine of the angle between the normal to the zone surface (direction of I) and the line from the zone center to the roadway observation point (calculation point) (Lambertian reflection)

Each zone is treated as a luminaire and calculations are completed using existing methodology .