In this final article of the series, looking at the main changes to BS5489 published in 2020, we discuss in more detail the section on product glare ratings, what the standards now recommend and why that matters.
What is Glare?
Glare is uncontrolled brightness or excessively strong lighting that can cause anything from slight discomfort to disabling loss of performance, or visibility. However, this is a subjective scale, as sensitivity to glare can vary widely. For example, older people often have greater sensitivity to glare due to the ageing characteristics of the eye. Nevertheless, reducing glare is an effective way to improve how well lit an area is.
Product versus Scheme
Whilst glare ratings on luminaires are useful, they’re not actually an indication of how glary a scheme will ultimately be. They suggest how glary that particular product is, in isolation. Let’s explain that further; glare in a product and in a scheme doesn’t necessarily mean the same thing. For example, a floodlight is typically a very glary product – especially if you stand looking up at one! However, when you go to a stadium to watch a game, the stadium isn’t considered too glary because it’s designed as a solution to light the vast area. Therefore, you can take a glary product and design it into a scheme that actually minimizes glare – and that’s achieved through good design practices.
How have glare standards changed in BS5489?
The standards changed in 2020 affecting how glare is handled; i.e. how to make the right calculations for glare on subsidiary roads, for P classes. The new approach prioritises the use of Threshold Increment (The percentage increase in contrast of an object that is needed to make it stay at threshold visibility in presence of disability glare generated by luminaires of a road lighting installation ) to evaluate a scheme, as opposed to an individual product glare rating.
What impact/benefits should this have?
I think the change of focus from glare ratings and G-classes, to designing a scheme properly and that being incorporated in the design calculation, should open up the competitive market. In some cases (not really for subsidiary roads of course), but in terms of P classes, lantern choice is restricted, especially when we get to the top end of the G ratings; G6 luminaires, for example. At the lower end, there is much more choice so the effect will be felt less. Certainly, designing a scheme where threshold increment provides the ultimate definition of whether a product is too glary or not, (as opposed to an isolated G-class rating) should mean there’s more choice for purchasers and designers when specifying.
Actually, using glare ratings as a product feature to compare between product offerings isn’t technically accurate; i.e “buy this product because it’s G6 and therefore better than a competitor’s because it is G3” That’s not how it works in a scheme. How the lighting is designed using the product is much more important.
Several years ago we had to design a G6 scheme and it used 25% more units than what was actually needed. To be honest, driving past, it still doesn’t look right because there are just too many columns! But that was because G6 was defined as the ultimate measure for controlling light.
Glare ratings and lighting design
Of course, ensuring no upward light into the sky directly from the luminaire is enormously important because that’s wasted light, no matter what your point of view. But the thing with LEDs is they’re so directional, so when you’re trying to achieve a good spacing and trying to spread the light out over the road to achieve that uniformity, you have to push the light out at quite a high level. As soon as you start limiting that (because the G rating doesn’t allow a certain amount of light past an angle), you’re going to trim it down, which means it will naturally bring the distribution in and then you won’t quite hit the spacing.
Plus of course, from a driver’s point of view, you don’t want that disability level of glare hitting your eyes.
Therefore, threshold increment is a far better definition of glare than the G-rating because everything can be factored in and blended into the scheme design. Potentially this may mean customers won’t need as many units, or Watts, to get the scheme designed properly.
The old standard said that, if you used white light on an S class road you could drop 25% of the lighting class. The SP ratio standards came in to reinforce that, (again it was 25% or thereabouts). This has since been removed with the current version. Some may make the assumption that you’d increase the lighting class back by 25%, but that’s obviously not directly true because you’re still using the same products with good SP ratios which, just because the SP ratio is not being demanded, are going to hit the lighting classes required.
So, aren’t you going to use more energy this way?
Because of the changing standards over time, it is an opportunity for misunderstanding, Some may assume that, by removing the SP ratios, you’re effectively saying you’re going to use more energy. But, again, if you design properly and use a good product with good optics and so on, then that won’t be the case. You should still see a massive saving. Potentially maybe 2% less, or in some cases more, but it will all balance out, and you are still using significantly less energy than the existing scheme.
I think the emphasis is to continue encouraging the industry towards achieving the right lighting level for the right application and no longer driving buyers towards cooler temperatures, focusing instead on more comfortable light sources to give a higher quality lit environment. Previously, you might have been penalized for using a warmer colour temperature due to the reduced S/P ratio, but not any longer. There is still an energy difference but that is continuing to reduce as LED’s become more efficient. Consideration should be given to the overall impact and effectiveness of the lighting scheme.
“It’s a more robust, technical approach”
The point about glare is that you’re using a method of scheme measurement for working out whether or not a scheme is glary, rather than measuring the product to work out whether the product used on that scheme will be glary. It’s just a much more technical way of doing it.
Essentially, where possible we need to calculate the threshold increment for a scheme and, only if you can’t calculate it, should you use a product’s glare rating. Previously glare ratings would be applied [without prejudice] across the board, which, particularly in a tender specification can result in a narrowing of the market and result in a far from optimum design solution.
Again, this change is all about improving the quality of the lit environment using a robust, technical approach.
In conclusion
There are obviously lots of groups that work on the development of British Standards; the BSI committees but also the ILP technical committee and lighting liaison groups. They will all have a contribution. So whilst they don’t write the standards, (that’s just done by the British Standards committee) all these groups do feed into the development process – for example providing input into how they’ve been using the current document, any problems or issues members have come across when putting designs together etc.
Now all the changes required have been written into the standards, it continues to reduce instances of certain elements being open to interpretation or different local areas adopting different approaches. As the transition to LED continues and the market matures, ultimately, this will lead to improved consistency and practice across the UK road infrastructure. And it narrows the scope for manufacturers to compete on metrics, or carve out nuanced product differences, that doesn’t actually add value for customers.
How INDO products line up with the new standards
INDO has solutions that offer variable adaptive lighting, trimming and part night dimming as standard, pre-programmed switch off – we can program that into the PCBA if being used independently from a central management system or other third-party control.
For schemes that require sensor control, such as passive infrared (PIR) motion sensors, presence detectors, push-button switches, of course, we have SiCURA our Sensory Ready luminaire
INDO products offer a range of optics meeting glare ratings between G1 – G4 depending on the light engine employed. Our OPUS2 and CHROMA LED light engines are designed with glare in mind, utilising larger and fewer individual LED light points thus providing a softer appearance whilst also delivering the performance expected from this type of product.