Bankside Yards Assessing Light

The High Court decision in Cooper & Powell v Ludgate House Ltd (2025), known as the Bankside Yards judgement, represents the most significant judicial commentary in a generation on assessing light for rights to light purposes. In Section VI of the judgment, Mr Justice Fancourt turns his attention to a foundational question for surveyors and courts alike:

"How should light be measured for the purpose of informing the Court's assessment of whether an interference has occurred?"

This question goes to the heart of rights to light practice. It speaks directly to the methods surveyors rely on to model light loss, to justify whether a loss is actionable, and ultimately to assist the Court in determining whether a nuisance has occurred.

The context of this ruling was the Bankside Yards redevelopment in London SE1, and particularly the impact of the 19-storey Arbor office building on neighbouring flats within Bankside Lofts.

This article examines the technical discussion in Section VI of the ruling, distilling key principles, summarising the contrasting light assessment methodologies, and reflecting on what the case means for assessing light going forward.

Waldram vs Radiance : Bankside Yards Competing Methods of Assessing Light

At the centre of the Bankside Yards case were two proposed methods of assessing light:

The Waldram Method

BS EN 17037 Median Daylight Assessments using Radiance software

The Claimants' surveyor used the traditional Waldram method, which assesses the distribution of daylight within a room by calculating the proportion of its area that receives at least 0.2% daylight luminance from a notional sky dome. This measurement is used to apply the '50/50 rule' – a threshold test where a room is considered adequately lit if more than 50% of its area meets the 0.2% criterion. This method, introduced over a century ago, uses the Waldram diagram to determine sky visibility through window apertures at a given grid height within the room.

The Defendants' surveyor (GIA) relied exclusively on an alternative approach, calculating Mean Daylight Factor (MDF) and Mean Daylight Illuminance (MDI), derived from software modelling using Radiance.

These were presented as alternatives to the traditional assessment, drawing from the principles set out in BS EN 17037:2018, the British Standard that provides guidance on the evaluation of daylight provision in buildings using metrics such as illuminance levels and daylight factors under standardised sky conditions. They presented both numerical results and false-colour visualisations to argue that the effects on light were negligible or unnoticeable.

The result was a forensic analysis by the Court of both methodologies.

The Court’s Rationale: Objective, Established, and Reliable

Mr Justice Fancourt carefully evaluated the assumptions, logic, and reliability behind each approach. His view was clear:

The Waldram method remains the primary and preferred means of assessing whether a room suffers a material loss of light.

The Radiance model may be used as supplementary evidence but must not override objective analysis with "impressionistic" visuals.

"If reliance on the Radiance methods ultimately comes down to a subjective and impressionistic assessment of false colour graphical representations of results, rather than the results themselves (as was the case here), then I question the value of that. It amounts to replacing an established, universally applied, agreed standard with the subjective opinion of an expert light surveyor – which was the opposite of what Percy Waldram attempted to do over 100 years ago."

The Judge reaffirmed that the Waldram method provides a consistent proxy for lux levels. Although it has limitations (e.g., it does not consider reflectance from internal surfaces or floor finishes), it is designed to offer a stable and uniform yardstick. In contrast, Radiance-based models, while technically sophisticated, carry a greater risk of subjective interpretation, especially when reliance is placed on visual renderings.

Commenting on the benefits of the Waldram method for assessing light loss versus those set out in the British standard, Justice Fancourt stated:

"The strength of the [Waldram] method is that it has been calibrated and shown to work over decades, and is accepted as the appropriate standard across the industry. There is no rival test for the sufficiency of light in a room as a whole that has been calibrated by testing and experience in the same way....there has been no proper calibration of the measurements to ascertain whether in practice the 2018 BS standards provide a sufficiently lit room. To the extent that the 2018 BS has significantly reduced the minimum standard set by the EU, this must be doubtful."

The Court took the view that the integrity of expert evidence depends on consistency, repeatability, and objectivity – qualities the Waldram method continues to offer.

Bankside Yards - Assessing Light and The Role of False Colour Images

GIA's reliance on Radiance-generated false colour images was a significant feature of their defence. They presented before-and-after images to demonstrate that light loss would be visually imperceptible to the average occupant.

The Court rejected this approach for several reasons:

Subjectivity: These images are inherently open to interpretation. Colours do not provide a consistent or measurable proxy for illuminance.

Lack of calibration: The image renderings were not backed by uniform lighting scales or benchmark thresholds.

Not a replacement for data: They are illustrative tools, not analytical ones.

In short, the Court was critical of GIA's attempt to use "subjective and impressionistic" visual impressions to override numerical data. This is an important reaffirmation of the role of established, measurable benchmarks in professional assessment.

Notably, this is not the first time GIA's expert evidence has been challenged in court. As highlighted in a previous article, GIA's methods and conclusions have previously drawn judicial criticism, with their assessments leaving councillors "significantly misled" in relation to daylight and sunlight assessments.

Use of Radiance for Corroboration, Not Substitution

Mr Justice Fancourt accepted that Radiance-based outputs, including MDF and MDI, could be informative if properly applied.

Indeed, in this case, the Radiance results broadly corroborated the Waldram results, confirming significant light loss in the claimants' flats.

However, the judgment makes it clear that Radiance should be used to support or contextualise findings from the primary method, not to replace it. The judge noted that a significant concern was the potential for selective use of modern tools to justify pre-determined outcomes.

For rights to light surveyors, this reinforces the importance of:

Maintaining consistency with historical methods;

Clearly explaining any supplementary metrics; and

Avoiding presentation techniques that may mislead or obfuscate.

Comparative Case Law

This case builds upon and reinforces principles from earlier judgments:

Colls v Home & Colonial Stores Ltd (1904) established the principle that a claimant is entitled to sufficient light for the "ordinary notions of mankind", not all the light previously enjoyed.

Wrotham Park Estate Co Ltd v Parkside Homes Ltd (1974) established the principle of "negotiating damages".

In Beaumont v Florala (2020), the Court accepted Waldram results as primary. GIA, this time acting for the Claimant, introduced radiance based analysis and false colour images to support the opposite contention they attempted to justify in the Bankside Yards case, stating that "even a small quantum of natural daylight is valued significantly by occupiers and users of that space". The false colour images were also seen as difficult to interpret, one expert stating that he "struggled to see the difference" between images. Negotiating damages of £350,000 were also awarded as in Bankside Yards, calculated at 33% of the developers profit.

The Bankside Yards judgement adds clarity to this jurisprudence by giving a firm endorsement of traditional methods while cautioning against the encroachment of interpretive techniques that reduce evidential objectivity.

Implications for Rights to Light Practice

The implications of this judgment are clear and far-reaching for practitioners:

Waldram Remains Primary: Surveyors should continue to rely on Waldram assessments as the main evidential basis for expert opinions.

Radiance Requires Caution: Where used, Radiance-based modelling must be numerically robust and carefully explained.

Avoid Impressionism: Visual outputs must not replace empirical data.

Expert Reports Must Be Defensible: Courts will scrutinise the basis and assumptions of light assessments and disregard unsubstantiated and subjective reports.

Key Takeaways

The judgment in Cooper & Powell v Ludgate House reaffirms the primacy of the Waldram method.

Daylight factor and illuminance-based methods such as Radiance have a place but must not supersede objective assessment.

Courts will reject approaches that rely on subjective visualisation rather than consistent numerical metrics.

The legal standard remains grounded in measurable, repeatable analysis of light distribution.

Conclusion - Bankside Yards Assessing Light Judgement

In summary, what does the Bankside Yards judgement tell us about assessing light for rights to light purposes? In short, the assessment of light must remain rooted in established, empirical methodologies.

The High Court gave unambiguous confirmation that the Waldram method remains the principal and most reliable standard for assessing whether an actionable rights to light infringement has occurred. Despite evolving technology, the judgment made it clear that credibility in court is secured through objectivity, repeatability, and measurable data—not through visual representations that rely on subjective interpretation.

The Court decisively rejected Radiance-based false colour visuals as a substitute for analytical evidence, describing them as impressionistic and lacking in calibrated rigour.

For developers, this ruling underscores the importance of commissioning surveyors who prioritise evidence-led assessments over presentation-led justification.

For surveyors, it serves as a reminder that expert opinions are grounded in robust and proven methodologies that can withstand judicial scrutiny.

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