Fluorescent colours appear brighter during daylight giving a high visual contrast for use in warning signs and on emergency vehicles and equipment. The colour pigments in these products are fluorescent when exposed to sunlight. The pigment absorbs energy in the near-ultraviolet and visible of the electromagnetic spectrum, then re-emits the energy as longer wavelength visible light. This light emissive property makes fluorescent signage brighter, of higher luminance and more colourful than ordinary traffic colours (Burns & Pavelka, p1).
This Ford Territory has high visibility fluorescent retroreflective livery. The picture has been taken in very low light at dusk. The colours take on an almost ethereal glow as they retransmit the reflected UV wavelengths. The times of low-light during dawn and dusk where this effect reaches its maximum are exactly when emergency services need heightened levels of visibility.
How Effective is Fluorescent livery?
The image at the right shows an ACT Ambulance sedan parked behind an ambulance and a support unit – both of these vehicles are in the old candy-stripe livery and are visually much closer and larger than the smaller sedan. Once your eye has located the yellow-green stripe on the sedan it keeps scanning back to the flourescent livery. If you try to look at the other vehicles which are much larger and more dominant in your field of view you will still keep returning to the sedan. Notice that the yellow-green fluorescent colour also takes your attention away from the high-visibility orange cones in front.
New studies have changed our thinking about how we react to fluorescent colours.
Over the last decade the general principle has been that humans notice fluorescent yellow-green because the maximum sensitivity of the human eye is centred on the yellow-green wavelengths (especially in the peripheries). The effect is most pronounced in yellow-green but there are other colours that can also fluoresence (red, orange & yellow). There may also be learning factors that amplify our response to these colours when they are seen. Certainly fluorescent colours are of greatest benefit when the observer is older than 40-50 years and has degenerative and age-related vision deficiencies
Emergency vehicle conspicuity research on livery, warning lights and
high visibility markings – photos, technical information & newsletters by John Killeen
VISUAL DETECTION AND RECOGNITION OF FLUORESCENT COLOR TARGETS VERSUS NONFLUORESCENT COLOR TARGETS AS A FUNCTION OF PERIPHERAL VIEWING ANGLE AND TARGET SIZE
Daytime conspicuity of targets with fluorescent and nonfluorescent backgrounds as a function of the peripheral angle and the target size was investigated in the field. The resulting peripheral detection and recognition data may prove relevant to, for example, a bicyclist or a pedestrian approaching a driver at an intersection from a side street, or to a construction worker approaching a driver in a road construction site. Two groups of nine young, healthy subjects were used. White, blue, green, red, fluorescent red, fluorescent yellow-green, yellow, fluorescent yellow, orange, and fluorescent orange were presented at peripheral angles to the right of the line of sight. The targets were presented at a radial distance of 30 m (100 ft) from the front bumper of the car at the selected peripheral angle. The subjects were seated in a stationary car and the targets were visible for 2 sec. Each subject provided a total of 180 observations. The results of this study indicate that the fluorescent color targets (especially the fluorescent yellow-green) were considerably better-detected peripherally than their nonfluorescent counterparts. Furthermore, for some peripheral angles fluorescent yellow-green was among the top three best recognized colors. On the basis of the results of this study, it may be concluded tentatively that to maximize daytime conspicuity for peripheral detection and recognition, highly conspicuous fluorescent colors such as fluorescent yellow-green, along with a fairly large target size, should be selected. It appears that however conspicuous a color is alone, if the target is too small for the visual angle subtended, the color will not be well detected or recognized, especially at larger peripheral viewing angles.
This paper appears in Transportation Research Record No. 1605, Research on Traffic Control Devices.
Posted on : DEC 26,2011