1 Daytime Visibility of Fluorescent Highway Signs Frank Schieber Heimstra Human Factors Laboratories University of South Dakota

2 Fluorescent Highway Signs The Phenomenon of Fluorescence Daytime Visibility Benefits for Traffic Control Devices Photometric Properties related to the Apparent Luminosity of Fluorescent Materials

3 What is fluorescence? Absorption of short- light that is subsequently re-emitted as longer- light

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5 Bispectral Reflectance Distribution Dual-Monochromator Spectrophotometer D.Couzin (June 18,1998) Fluorescent Red-Orange

6 Spectral Power Distribution Fluorescent Red-Orange Y total = Y r + Y f Y r = 7.3 Y f = 23.2 Y total = 30.5

7 Benefits of Fluorescent Highway Signs

8 Jennsen, et al. (1997) Flourescent: Yellow and Yellow-Green Fluorescent signs detected and recognized at greater distances Recognition advantage: young drivers:57 m ( k/m) old drivers:90 m ( k/m) Eye movement field study: Fluorescent signs first fixated at greater distances and less likely to be skipped

9 Zwahlen & Schnell (1997) Peripheral Field Conspicuity briefly presented signs of varying size, color and eccentricity fluorescent signs detected and recognized at greater distances than their non-fluorescent counterpart

10 Hummer & Scheffler (1999) Workzone Driver Behavior Fluorescent Orange versus Non-Fl. Orange (“Left Lane Closed Ahead”) (4) Treatment and (3) Control sites 5 month Observation Period Drivers vacated left lane sooner in workzones with Fluorescent Orange Signs Traffic Conflicts (n.s.)

11 Burns & Pavelka (1995) Subjective Appearance/Evaluation Orange, Red, Yellow, Yellow-Green, (Green) Pair-wise comparisons of disk targets against “camouflaged” background Visibility (Can you see either target?) Recognition (What color are the targets?) Relative Conspicuity (Which is more noticable?) Fluorescent signs consistently superior

12 Burns & Pavelka (1995) Detection Performance

13 Burns & Pavelka (1995) Detection Performance

14 Burns & Pavelka (1995) Recognition Performance

15 Burns & Pavelka (1995) Recognition Performance

16 Burns & Pavelka (1995) Fluorescent targets had higher luminance contrast against the multi-colored background

17 Burns & Johnson (1997) Appearance at Dusk Investigated possible photometric mechanism for apparent increase in relative conspicuity of fluorescent signs at dusk and under overcast sky Fluorescent: Orange, Yellow, Yellow-Green Subjective rating of brightness (lightness) 1 hour before - half hour before sunset

18 Changes in Perceived Lightness and Luminance Contrast approaching and following sunset Lightness Luminance Contrast

19 Fluorescent Orange versus Orange Fluorescent Yellow versus Yellow Fluorescent Yellow-Green versus Yellow

20 Twilight/Overcast Sky Clear Noon Sky Four Phases of Daylight

21 Relative Spectral Radiance Distributions under Clear versus Overcast Skies

22 Some Theoretical Considerations

23 Evans’ (1959; 1974) Stimulus Configuration 1  Test Field Variable Luminance Constant chromaticity 10  Achromatic Surround Constant Luminance (318 cd/m 2 )

24 Evans’ Fluorence Threshold G 0 = log( Surround/Target Luminance) Illuminant mode –Surround Luminance “Fluorence” (Farbenglut) –G 0 (Zero Gray) Colorful with gray Black Target Luminance Lowest High Target Appearance

25 Evans (1969) Fluorence Threshold G 0 = log( Surround/Target Luminance) Doesn’t this function look familiar?

26 Monty Burns function???

27 Spectral Saturation Function

28 Inverted Spectral Saturation Function

29      Fluorescent Yellow- Green (.410,.571)  Fluorescent Yellow (.533,.460)  Fluorecent Orange (.625,.367)  Fluorescent Red (.680,.301) High Colorimeteric Purity of Fluorescent Colors...

30 Modeling Appearance Data for Targets of Variable Fluorescence

31 Perceived Luminosity as a function of Excitation Purity (i.e., Saturation) (Data from Thielert & Schliemann, JOSA, 1972)

32 Perceived Luminosity as a function of Total Luminous Reflectance (Y)

33 The MacAdam Limit (Y max for a given Chromaticity)

34 3D MacAdam Limit Surface

35 Perceived Luminosity as a function of the MacAdam Limit for Target Chromaticity (x,y)

36 Perceived Luminosity as a function of Total Luminous Reflectance (Y) normalized to the MacAdam Limit

37 The End. Thanks for Listening!