Building on his keynote presentation to June’s Centenary Lighting Summit, Allan Howard explains the factors driving growing concerns around vehicle headlight glare at night, and asks what the industry can be doing about it.
Don’t get me wrong, I enjoy driving but, as I will explain, developments in car design and vehicle lighting are raising concerns.
These concerns, in turn, are leading to people preferring not to drive at night but also to safety worries regarding vehicle lighting systems by both day and night, and not just for the motorist.
Since 2001, it is estimated that cars have grown by an average of 0.5cm per year. The average car width has now passed 1.8m, which makes them wider than the minimum standard car parking space in many countries. The image of the two minis below illustrates this trend clearly.
With the development of SUVs and bigger cars, the driver observer height has changed and now varies greatly.
Yet, when we design for highways based upon luminance, we look to achieve a performance level based upon a driver eye hight of 1.5m. Civil engineers, when they design roads and consider object detection use the range 1.05m to 2.0m.
So, are we right to retain the 1.5m observer hight? Does the observer hight have much of an effect when considering luminance levels, especially regarding uniformities? We don’t seem to know.
As cars have developed, we have also seen an increase in the size and profile of windscreens, they are now much larger and have an increased rake.
Further, the situation is not helped by LED luminaires essentially being a non-uniform light source and these factors, perhaps, require us to review how threshold increment is assessed and calculated.
RAC SURVEY
An RAC survey suggests that more than four out of five (85%) of drivers affected by headlight glare believe the problem is getting worse. In summary:
- 89% think some car headlights are too bright.
- 67% say that being dazzled forces them to slow down considerably.
- 64% believe some headlights are so bright they risk causing accidents.
As reported in the March 2024 edition of Lighting Journal, the report led by Baroness Dianne Hayter of the House of Lords into ‘Modern vehicle headlights dazzle drivers and may compromise road safety’ draws similar conclusions (‘Blinded by the (oncoming) light’, vol 89 no 4).
It is not just an issue with headlights, but also with taillights and daytime-running lights (DRL).
There are various factors that need to be considered.
The driver’s rear view of approaching cars in their rear-view mirrors is not a great concern, as these mirrors apply a filter and thus head lights and DRLs appear not to be so bright. The problem is the view in wing mirrors (peripheral and direct) which have no filter. So headlights/DRLs can be very bright.
They then become, at best, a source of discomfort glare whilst driving or, worse, a source of disability glare, especially when considering pulling out and or lane changing.
For drivers in lower vehicles this is exacerbated as headlights in higher vehicles can align with their wing mirrors.
Research presented by Nilsson Tengelin, M et al at the CIE 30th Quadrennial 2023 ‘A novel method for field measurements of light distribution of modern vehicle headlamps’ reported on single headlamp beam intensities and the range of intensities measured are concerning.
- Low beam: 14,400 cd (halogen) to 43,300 cd (LED)
- Full beam: 41,100 cd (LED) to 186,100 cd (LED).
The colour temperatures also vary from warm through to very cold white. The actual beam distribution, too, greatly varied across a wide range of vehicles for both main and full-beam settings, so there is no consistence in beam distribution.
As you may have noticed, too, daytime running lights have fast become a brand identity for many car manufacturers. They are getting larger and brighter and can be made up of individual LEDs (non-uniform light source) or appear as one light source (uniform light source).
To understand one of the concerns with DRL, we first need to understand phantom arrays. This is an effect you experience when making rapid eye movements, what is termed a saccade, and the eye detects a series of multiple or ghost images.
This is particularly noticeable with both rear-tail lighting and daytime running lights. The effect is more evident if the lights are vertical, but shape and brightness contribute to the effect when seen.
A Joint Research Project within the European Metrology Programme for Innovation and Research ‘Metrology for Temporal Light Modulation’ reports this to be a problem when drivers make rapid eye movements looking in their wing mirrors.
CONCLUSIONS
So, the challenges ahead. First, I’d argue we need new standards, requirements, and training for MOT testers to pick up LED retrofit lamps and fail those lights.
Second, we need to be the car industry to listen and make changes. What can be brought in to make them do this rather than carry on making lights brighter and using this as a sales pitch?
Third, I’d like to see the ILP consider its position, get to the table, and bring its expertise to bear; we can then help with resolutions.
Fourth, do we need to review the road lighting standards? The CIE has started the discussion regarding the observer view ahead. So, should we consider the observer hight above the carriageway and should we consider how we re-assess street lighting glare/threshold increment?
These are a lot of issues more than just bright headlights. We are at the start of a journey and the debate is underway with a great deal to be considered, researched and evidenced.
Allan Howard BEng(Hons) CEng FILP FSLL is WSP group technical director, Lighting & Energy Solutions
ACKNOWLEDGEMENTS
With thanks to:
- MetTLM-project (i.e, Metrology for Temporal Light Modulation; 20NRM01)
- Nilsson Tengelin, M. et al CIE 30th Quadrennial 2023
- Baroness Dianne Hayter report
- RAC, Rod Dennis
- Royal Collage of Optometrists
- This is an abridged version of the article that appears in the September edition of Lighting Journal. Click on the link to the edition to read the full article.
