Evaluating Roadway Lighting Systems Using Unit Power Density By David M. Keith Street and Area Lighting Committee Conference 2001 Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

What is Unit Power Density? Unit Power Density (UPD) is the energy for lighting -------------------------------- divided by the area of the roadway units: Watts / square foot or Watts / square meter (W/ft2) (W/m2) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD Calculation UPD = #Luminaire * (1.15*Watts/luminaire) ----------------------------------------------------- (LumCycle * #Lanes * Width of each lane) #Luminaire = 2 for staggered arrangement 1.15 factor to match previous work in IESNA publication LEM-6-1987 LumCycle is twice the “spacing” for staggered Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Why use Unit Power Density? more appropriate than using spacing spacing definition differs with layout spacing is inversely proportional while UPD is directly proportional includes ballast losses, reflects technological opportunities more universal, useful for different comparisons Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Why use Unit Power Density? more appropriate than using money UPD is a less complex, more stable evaluation focuses on the lighting system does not reflect specific utility costs does not reflect “the cost of money” UPD is less specific, more generally useful to public Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Why use Unit Power Density? applies to roadway lighting systems (not luminaires!) corresponds to relative costs in energy & pollution installation & equipment operation & maintenance evaluation of relative performance and savings through comparisons less valid comparing different wattages or sources does not address: aesthetics, light trespass, and many other important lighting issues Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

What are the components of a Roadway Lighting System? “Roadway Lighting System” includes: luminaire and lamp (source and wattage) roadway dimensions and surface geometry of layout, height & overhang (setback) operation and maintenance characteristics design criteria Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Why Roadway Lighting Systems? overall performance reflects trade-offs wattage, mounting height, overhang & spacing maintenance program cutoff classifications source types design methods value in comparisons of related cases directly proportional changes some comparisons are more valid than others Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Why Roadway Lighting Systems? NOT limited to evaluating a luminaire's physical or photometric characteristics shape or materials photometric distributions or cutoff categories allows comparative evaluation of luminaire and lamp geometry of layout, height & overhang (setback) operation and maintenance characteristics design criteria Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Design Criteria ANSI/IESNA RP-8-00 American National Standard Practice for Roadway Lighting Revised in 2000 three separate design methods Illuminance Luminance Small Target Visibility (STV) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Design Methods: Illuminance Illuminance method classical - 1928 lighting system alone lamp, luminaire and photometry system geometry one uniformity criterion: average to minimum no constraint on Emax now includes veiling luminance criterion constrains Lvmax, from luminance calculation Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Design Methods: Luminance Luminance method recent - 1983 roadway and lighting system interaction lamp, luminaire and photometry system geometry roadway surface two uniformity criteria average to minimum, maximum to minimum ”moving observer” & glare calculations Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Design Methods: STV Small Target Visibility method (STV) brand new in 2000 document unfamiliar and complex metric VL uses luminance, both horizontal and vertical contrast weighted over entire roadway veiling luminance included extension of luminance calculations radically different design techniques not suitable for optimization Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Roadway Lighting Criteria Classifications Eavg Eavg / Lavg Lavg / Lmax / Lveil / Roadway Area R3 Emin Lmin Lmin Lavg (lux) (cd/m2)   Major Med 13.0 3.0 0.90 3.00 5.0 0.3 Collector Med 9.0 4.0 0.60 3.50 6.0 0.4 Local Med 7.0 6.0 0.50 6.00 10.0 0.4 Source: ANSI/IESNA RP-8-00 All system calculations meet entire set(s) of criteria – averages, uniformities & glare Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Sources high pressure sodium (HPS) or metal halide (MH) difference in Light Loss Factor (LLF) - at end of life! probably have one or two luminaires contributing to point 0.7 for HPS 0.5 for MH “both should be even lower” difference in lamp life and in maintenance does represent pulse start MH (vertical lamps) better rated lumens but same LLF (mean @ 40% of life) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Lamp and Luminaire Data Lamp Wattage Rated Lumens Input Watts LLF   HPS 150 16,000 166 0.70 250 27,500 295 0.70 400 50,000 460 0.70 MHP 175 17,500 210 0.50 250 21,500 295 0.50 400 44,000 455 0.50 Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Cutoff Classifications relative to lamp lumen rating combination of intensity limits in two separate zones both just below and anywhere above horizontal FC CO SC Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Photometric Files Lamp Wattage All FC CO SC NC HPS 150 67 17 21 14 15 250 70 30 19 14 7 400 97 28 36 21 12 All 234 32% 32% 21% 15% MH 175 59 25 6 15 13 250 47 27 4 9 7 400 47 20 16 4 7 All 153 47% 17% 18% 18% All 387 38% 26% 20% 16% Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Roadway and Lamp Wattage Roadway Class -------------------------------------------------------------- Width Lanes Local Collector Major (m) 4 1 150/175 & 250 150/175, 250 & 400 250 & 400 7 2 150/175 & 250 150/175, 250 & 400 250 & 400 10 3 150/175, 250 & 400 250 & 400 13 4 250 & 400 17 5 250 & 400 20 6 250 & 400 Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Optimization For each combination of “photometry & roadway” Find the geometry with max. luminaire cycle Over a range of mounting heights and over a range of setbacks/overhangs Meeting entire set of appropriate criteria Result is “best” for combination – but may be impractical (too high or out over road) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD vs Avg Luminance: Collector 2 Lanes 250W HPS Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Cutoff Classifications for 250W HPS, photometric file distribution is Lamp Wattage All FC CO SC NC HPS 250 70 30 19 14 7 43% 27% 20% 10% Best (lowest) UPD values mostly SC or NC in “Best 5”, all SC or NC in “Best 10”, one is CO and all others SC or NC best FC is tied for 13th best UPD value Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD vs Avg Luminance: Collector 2 Lanes 250W MHP Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Cutoff Classifications for 250W MH, photometric file distribution is Lamp Wattage All FC CO SC NC MH 250 47 27 4 9 7 57% 9% 19% 15% Best (lowest) UPD values mostly SC or NC in “Best 5”, all SC or NC in “Best 10”, one is FC, others all SC or NC best FC is 9th best UPD value Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD vs Avg Luminance: Collector 2 Lanes 250W HPS Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD vs Avg Luminance: Collector 2 Lanes 250W MHP Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Sources: HPS vs MHP UPD (W/m2) #Averaged HPS MHP %Incr to MHP Best 1 0.56 0.85 51% Best 3 0.57 0.86 50% Best 5 0.58 0.86 50% Best 10 0.59 0.91 54% Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Design Methods Base calculations meet criteria for BOTH illuminance and luminance methods this is the most conservative approach recalculate for meeting criteria of either illuminance method OR luminance method different criteria, same optimization procedure compare each luminaire’s performance under each single method to Base (BOTH methods) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD by Design Method: Collector 2 Lanes 250W HPS Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Design Methods: HPS UPD (W/m2) #Avgd Base Illum Lum %Decr to Lum Best 1 0.56 0.56 0.40 -29% Best 3 0.57 0.57 0.41 -28% Best 5 0.58 0.57 0.43 -24% Best 10 0.59 0.59 0.46 -23% Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD by Design Method: Collector 2 Lanes 250W MH Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Design Methods: MH UPD (W/m2) #Avgd Base Illum Lum %Decr to Lum Best 1 0.85 0.85 0.46 -46% Best 3 0.86 0.86 0.55 -36% Best 5 0.86 0.86 0.60 -31% Best 10 0.91 0.89 0.66 -27% Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Lamp Output corresponds to the product of: Light Loss Factor (dependent on maintenance) Rated Lumens (dependent on lamp technology) for one lane roads with HPS luminaires, make separate calculations for LLF of 0.50 or 0.70 40% LLF increase ~ 16% UPD decrease (3:1) for all MH, replace standard with Pulse-Start each 2% lumen increase ~ 1% UPD decrease (2:1) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Overhang Limits overhang may be restricted by utility or jurisdiction (it’s a maintenance safety issue) recalculate all 250W HPS and MHP for overhang <= zero (Oh<=0) allow setbacks, but no luminaires over roadway typically no effect or increase UPD up to 15% may change which files have lowest UPD values increase greater for wider roadways Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

What are the characteristics of a Roadway Lighting System? “Roadway Lighting System” includes: luminaire and lamp (source and wattage) roadway dimensions and surface geometry of layout, height & overhang (setback) operation and maintenance characteristics design criteria uplight (like skyglow but more specific to lighting) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

What is Unit Uplight Density? Unit Uplight Density (UUD) is the uplight from lighting -------------------------------- divided by the area of the roadway units: lumens / square foot or lumens / square meter (lms/ft2) (lms/m2) Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UUD Calculation UUD = Uplight + ReflfromRoad + ReflfromOffRoad --------------------------------------------------------- (LumCycle * #Lanes * Width of each lane) Uplight: all “up lumens” (2 luminaires for staggered) ReflfromRoad: 0.07 * lumens onto the roadway ReflfromOffRoad: 0.18 * “down lumens” not on road Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Uplight with the “best six” luminaires from 400W MHP on 4 lane Major road two FC, two CO and two NC all have full spherical photometric data evaluate Unit Power Density (UPD) and Unit Uplight Density (UUD) for each luminaire does more cutoff correspond to less uplight? does system efficiency (UPD) correspond to uplight? Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

UPD vs Avg Luminance: Major 4 Lanes 400W MHP Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing UPD and UUD Base UPD Base UUD (W/m2) (lms/m2) FC 0.78 3.8 NC 0.74 4.0 NC 0.73 3.9 Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Uplight with the “best six” luminaires evaluate UPD and UUD for each luminaire revise conditions for overhang <= 0 (luminaire not over roadway) for Luminance design method for Small Target Visibility (STV) design method compare trends and UPD-UUD relationship across different conditions Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Uplight: UPD Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Uplight: UUD Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Comparing Uplight more stringent cutoff (FC or CO) does not necessarily correspond to less uplight as UPD increases, UUD increases as UPD decreases, UUD decreases changes in UUD are nearly (but not always) proportional to changes in UPD more efficient lighting system (lower UPD) does correspond to less uplight Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Summary of UPD Comparisons deltaUPD corresponds strongly to deltaUUD deltaUPD is ~ 1/2 to 1/3 of deltaLampOutput UPD drops up to 25% for Luminance method UPD drops up to 35% for STV method systems with lowest UPD values typically have distributions with less stringent cutoff When full cutoff distributions are required, what is the increase in UPD? Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

% Increase (any Wattage) in Base UPD for “Full Cutoff Required” Road Local Collector Major #Lanes 1L 2L 1L 2L 3L 1L 2L 3L HPS Best 5 20% 17% 15% 17% 18% 12% 14% 15% Best 10 30% 28% 27% 28% 18% 17% 18% 16% MH Best 5 19% 19% 18% 22% 20% 13% 14% 12% Best 10 21% 22% 20% 22% 24% 16% 15% 13% Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

% Increase in UPD for Full Cutoff Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Conclusions of UPD Evaluations There is a substantial potential for reductions in equipment, costs, energy use & uplight which correspond to lower Unit Power Density values for roadway lighting systems. Comparing systems can lead to results which may be counterintuitive (FC ~ less efficiency). The best use of this work may be for comparisons with specific UPD values developed from proposed roadway lighting systems with similar characteristics. Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056

Evaluating Roadway Lighting Systems Using Unit Power Density By David M. Keith for a copy of this presentation: resodance.com/mdi/SALC2001.html for questions or more information: keithd@resodance.com Marshall Design, Inc. 1534 Marshall Road Boulder, CO 80305 303-499-2056