Though the effectiveness of blue emergency lighting in daytime conditions has become a matter of contention with many first responders, there has long been universal agreement that warning lamps of higher intensity (brightness) are measurably more effective for daytime conditions, regardless of their colour. However, by the same token, the issue of motorists being blinded or pedestrians being “masked” by high-intensity warning lights used at night continues to fuel debate (or at least prompt calls for further research). This explains the growing interest in the need to strike a balance between high-intensity lighting that is essential for daytime and the reduced-intensity lighting that could be used for night operations.
Finding compromise in a single intensity output that is bright enough for daytime, but still addresses the glare and masking issues associated with night operations is a difficult task that, at least for some, may entail unacceptable performance trade-offs. For this reason, several research studies have suggested that employing at least two different levels of light intensity may be the best solution to avoiding a trade-off that even mildly compromises conspicuity performance and safety issues.
Based on the results of their experiments, and taking into account past research and practical experience, Professor Michael J. Flannagan of the University of Michigan’s Transportation Research Institute, explains that limiting warning lamps to a single intensity, “…appears to require a compromise between having lamps that are intense enough for daytime conditions and lamps that are not too intense for night conditions.” He goes on to say: “While it may be possible to fine-tune a single compromise level to produce the best overall effect, using at least two levels [one for daytime and another for night] would probably be better than the best possible compromise.” Flannagan suspects future research may well prove that it would be even more advantageous to incorporate a much broader menu of intensity level options adapted to a more tightly defined set of ambient light conditions – for example, higher intensity levels in full sunlight than in daytime cloudy or foggy conditions; and further adjusted intensity levels to compensate for the lack of contrast against ambient light at dawn and dusk).
Adapting light intensity to ambient lighting conditions is not a new idea. However, in quantifying differences by analysing performance between day and night operations, current research data adds weight to the argument in favour of an adaptive approach. At least at this point in time, there are some drawbacks – not the least of which have been cost and reliability. There is also the potential for misuse by vehicle operators choosing to always opt for the higher daytime intensity levels, and even override automatic controls (including covering light sensors) because of the operators’ own perception that brighter levels are always more effective.
Flannagan responds by pointing to recent technological developments that may offer effective alternatives in addressing these potential drawbacks. Chief among these alternatives are the more economical and extremely reliable LED light sources that can be readily adjusted to produce multiple light levels from the same lamps. Take NARVA’s self-contained LED warning light range, for instance, which features a “dim mode” that reduces light output when vehicle park lights are switched on. In addition to the substantial improvement in warning system flexibility available through LEDs, better automatic controls for day and night conditions may soon encompass sensing of time and position from increasingly more affordable GPS capabilities.
In terms of suggestions regarding emergency vehicle lighting, the Transportation Research Institute’s Effects of Warning Lamp Color and Intensity on Driver Vision focuses on two key considerations: First, the need to evaluate the benefits of varying lamp intensity levels between day and night operations. And secondly, acknowledging the potential for increasing the overall use of blue for all operations – both daytime and nighttime.
Moreover, “The apparent advantage of blue for conspicuity would seem to favour the broader use of blue warning lamps on all types of emergency vehicles,” says Flannagan, noting that this has long been the case in Europe. Beyond the basic visibility performance criteria that was the primary subject of his organisation’s research, Flannagan goes on to suggest that practical considerations, such as the capability of today’s LEDs to produce effectively conspicuous blue light relatively easily in comparison with the previous option of filtering incandescent white bulbs, further supports the broader use of blue lighting.
It would be difficult to argue against a broad consensus: When asking for right of way, including at night, maximum light intensity may provide the greatest level of warning around an emergency vehicle. This approach is not without those obvious but often-ignored drawbacks, though. The glare produced by warning lamps used at high intensity light levels (often referred to as night blindness) is certainly an issue with regards to motorist visibility. Based on his organisation’s research, however, Flannagan points out that nighttime “masking” is only one factor that impairs visibility.
Beginning with the premise that motorists’ vision is inherently impaired in nighttime conditions, and that automotive headlamps are generally considered to be an incomplete solution, Effects of Warning Lamp Color and Intensity on Driver Vision points out that even with no glare at all, visibility of pedestrians without retroreflective markings is very poor. The study goes on to emphasise that when pedestrians are equipped with adequate retroreflective markings, even very high levels of warning lamp glare may not reduce visibility below acceptable levels.
As we have moved away, in most cases, from a Halogen and Strobe era to an LED environment, with respect to lighting on emergency services vehicles, we have also seen great advances in LED technology which includes light intensity. Agencies have embraced the advantages of using LED over older alternatives, as it offers more flexibility in these ways and more: Ease of install; the ability to choose a desired flash pattern with the ability to synchronise multiple lights; significantly lower power draw on electrical systems; and optional sizes (different length LED bars).
With these developments in technology have come incredible increases in light intensity and therefore the need to adopt it responsibly. For night operations, agencies have wanted this intensity to be reduced to prevent motorists from being blinded by the impact of these lights operating at full power. Fortunately, LED manufacturers listened to this and introduced a “dim” feature mainly for use at night operations.
To achieve this, manufacturers of light bars and surface mount LEDs were able to offer not one but two possible solutions: 1. Connecting a supplied dim wire within the loom of a light bar or LED to the parker lights headlight switch on a vehicle which dims all the lights automatically (usually reduces intensity by 50%), and 2. The installation of a low light sensor into the light bars on or under the light bar lens (similar to the automatic headlights featured in many modern passenger vehicles).
These methods have been adopted by agencies and departments for many years now. Although not all ask for this requirement, it has gained popularity since it was introduced. One agency had a requirement for the “dim” feature to be reduced further, cutting intensity by 60%. This was easily achieved by reprogramming the circuit board within these light heads or control boards.
At NARVA, we are very much looking forward to the next generations of lighting technologies – laser, or similar – which will no doubt provide even more flexibility, safety and attention for our emergency service lighting market.
For more information, go to www.narva.com.au