Sources & Surfaces Evaluating Spectral Distribution Interactions Using Roadway Signage IESNA Roadway Lighting Committee April 2003 David M. Keith, FIES & Jefferey F. Knox

Sources & Surfaces: Overview Our world is not all shades of gray, but... “Lumen” is spectrally ignorant by definition Therefore, since we use color to communicate especially important information such as should we evaluate visibility using full spectral information that describes color?

Sources & Surfaces: Background Luminous reflectance: Any of the geometric aspects of reflectance in which both the incident and the reflected flux are weighted by the spectral luminous efficiency of radiant flux V(λ). Note: Unless otherwise qualified, the term “reflectance” means luminous reflectance. Sources: “GLOSSARY OF LIGHTING TERMINOLOGY” IESNA Lighting Handbook, 9th edition & IENSA RP

Sources & Surfaces: Background Reflectance = Lumens off  Lumens on This means that “reflectance” is specific to each source’s spectral power distribution’s interaction with the surface’s spectral reflectance distribution Contrast is calculated using reflectance

Sources & Surfaces: Background Reflectance for surfaces is typically reported with no mention of the source being used in the evaluation, e.g. Figure 1-36, IESNA Lighting Handbook, 9th edition ANSI/IESNA RP-8-00 luminance calculation procedures (Annex A & IESNA Handbook, Figure 22-1)

Sources & Surfaces: Background Reflectance for many (most?) exterior surfaces is only marginally dependent on source SPD, because most natural surfaces are approximately “gray” Colored surfaces may be dependent on SPD interactions - how to find out? Roadway signage is familiar, available & important example for such investigation

Sources & Surfaces: Procedure Collect spectral data for exterior light sources and signage surfaces Combine using spectrally informed procedures to establish reflectances Combine into appropriate pairs for calculating contrast values Repeat with CIE LAB procedures for color difference evaluations

Sources Used in this Work Equal Energy constant radiation across the entire spectrum D65 a ‘daylight’ source of 6500 K from CIE Illuminant A an incandescent source of 2850 K from CIE HPS SPDs of four High Pressure Sodium wattages MH SPDs for Metal Halide Sources 250 or 400 watt, universal or horizontal Fluorescents four different CCT’s: 30, 35, 41 & 65

Sources Used in this Work SourceAbbr. x yCCTCRI Equal EnergyEqE * CIE D65C_D CIE Illuminant AC_A HPS 100WH HPS 150WH HPS 250WH HPS 400WH MH 250W HorizM2h * MH 250W UnivM2u * MH 400W HorizM4h * MH 400W UnivM4u * Fluorescent 3000KF Fluorescent 3500KF Fluorescent 4100KF Fluorescent 6500KF

Surfaces Used in this Work Roadway signage films manufactured materials, not paints Three different series from 3M Engineer Grade (ENG) High Intensity Flexible Workzone Sheeting (HIS) Visual Impact Sheeting (VIS) a.k.a. Scotch Lite Diamond Grade

Surfaces Used in this Work each series has multiple colors white yellow red green blue two series (HIS & EG) also have brown orange

Surfaces Used in this Work All meet FHWA Specifications CIE D65 CIE Illuminant A x y x y WhiteENG HIS VIP BlueENG HIS VIP GreenENG HIS VIP YellowENG HIS VIP OrangeENG HIS RedENG HIS VIP BrownENG HIS

Procedure: Reflectance Lumens on Lumens on = K*  [S( )*v( )] Lumens off Lumens off typical = ρ average * {K*  [S( )*v( )]} Lumens off revised = K *  [ S( ) * v( ) * ρ ( ) ]

Reflectances EqE C_D C_A H10 H15 H25 H40 M2h M2u M4h M4u F30 F35 F41 F65 White ENG HIS VIP Blue ENG HIS VIP Green ENG HIS VIP Yellow ENG HIS VIP Orange ENG HIS Red ENG HIS VIP Brown ENG HIS

Reflectances EqE C_D C_A H10 H15 H25 H40 M2h M2u M4h M4u F30 F35 F41 F65 White ENG HIS VIP Blue ENG HIS VIP Green ENG HIS VIP Yellow ENG HIS VIP Orange ENG HIS Red ENG HIS VIP Brown ENG HIS

Reflectances EqE C_D C_A H10 H15 H25 H40 M2h M2u M4h M4u F30 F35 F41 F65 White ENG HIS VIP Blue ENG HIS VIP Green ENG HIS VIP Yellow ENG HIS VIP Orange ENG HIS Red ENG HIS VIP Brown ENG HIS

Reflectances: HPS vs MH High Pressure SodiumMetal Halide AvgStDevAvgStDev HPS/MH White ENG HIS VIP Blue ENG HIS VIP Green ENG HIS VIP Yellow ENG HIS VIP Orange ENG HIS Red ENG HIS VIP Brown ENG HIS

Procedure: Contrast C = (L max - L min ) / (L max ) C mod = (L max - L min ) / (L max + L min ) For a perfectly diffuse reflector (or surfaces with similar reflectance geometric properties) Luminance = Exitance   Exitance = Lumens on * Reflectance C = (ρ max - ρ min ) / (ρ max ) C mod = (ρ max - ρ min ) / (ρ max + ρ min ) Still calculated in lumens (more accurately determined)

Procedure: Contrasts Color pairs determined by common sign combinations white - red(Stop, Yield, One-way) black - orange(work/construction, detour) black - yellow(caution, warning, advisory) white - green(information, direction, exit) Combinations evaluated using sign films in the same series e.g. ENG red & ENG white, HIS red & HIS white, VIP red & VIP white

Procedure: Color Difference Color Difference Threshold The difference in chromaticity or luminance between two colors that makes them just perceptibly different. The difference may be in hue, saturation, brightness (lightness for surface colors) or a combination of the three. This model more accurately reflects foveal vision which does not see in black & white - for example observe the horizontal line above - as it shades from black to white, it remains visible against the colored background (or does it?)

Procedure: CIE L*a*b* First, the illuminant in the local context can be specified, also in terms of the R, G and B cone outputs, as a reference white. The model treats all colors as a combination of surface color and illuminant color, which allows the model to be applied across a wider range of viewing conditions. Second, the trichromatic XYZ "primaries" are transformed mathematically to represent the Y/B and R/G opponent dimensions (along with a lightness or white/black dimension), which allows the models to reproduce the basic structure of color experience.

Procedure: CIE L*a*b* Finally, CIELAB is based on a set of imaginary “primary” lights that have been chosen specifically to make the color space perceptually uniform (at least, to the degree possible in a three dimensional model). That is, a difference of 10 units on the lightness dimension has the same perceptual impact as a 10 unit difference on the Y/B or R/G dimensions -- either separately or in combination. delLAB (ΔLAB) is the Euclidean distance between two color loci in the CIE L*a*b* space ΔLAB = {(ΔL) 2 + (Δa) 2 + (Δb) 2 } 1/2

C & delLAB: white - red ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: white - red ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: white - red ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - orange ENG Series HIS Series Source C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - orange ENG Series HIS Series Source C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - orange ENG Series HIS Series Source C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - yellow ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - yellow ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: black - yellow ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: white - green ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: white - green ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

C & delLAB: white - green ENG Series HIS Series VIP Series Source C Cmod dLAB C Cmod dLAB C Cmod dLAB EqE C_D C_A H H H H M2h M2u M4h M4u F F F F

“How to use these results” If signs are “iconic” - the image is what matters, not the information within - then reflectance of the surface should be maximised contrast and delLAB values are not as important Stop signs’ highest reflectance from C_A and HPS If signs are “informational” (read text) then reflectance is not as important contrast and delLAB should be maximized work, caution and “direction/exit” colors have highest values from HPS (nearly as high for C_A)

Future Work Investigate additional colors and surfaces Incorporation of appropriate mesopic spectral luminous efficiency function(s) for foveal vision Application of a model for evaluating age effects Further investigate appropriate color difference models (such as CIE LAB)

Summary Keep the spectral information in the calculation procedure Spectral effects of illuminants cannot be evaluated without considering the spectral reflectance of the lighted surfaces All this is evaluated as single bounce applications (no inter-reflections!)

Sources & Surfaces This work was solely supported by Luminous Design, Inc & Marshall Design, Inc who gratefully acknowledge the assistance of: 3M for data on signage reflectance Philips Lighting for lamp SPD’s

Sources & Surfaces Evaluating Spectral Distribution Interactions Using Roadway Signage IESNA Roadway Lighting Committee April 2003 David M. Keith, FIES & Jefferey F. Knox