Daylight and Sunlight assessments explained, and why they are not Rights of Light

The “green light” trap

A common line neighbours hear is: “We’ve passed the Daylight and Sunlight assessment, so there’s no issue.”

That is usually a deflection. A Daylight and Sunlight report is mainly a planning amenity document. A Right to Light claim is a private property right. They use different methods, different thresholds, and they answer different legal questions.

Two systems, two tests

What planners test (Daylight and Sunlight)

Local authorities commonly assess daylight and sunlight impacts by reference to BRE guidance (often called BR 209). It is guidance intended to be applied flexibly, not a strict legal pass or fail rule.

One of the best-known planning metrics is Vertical Sky Component (VSC). In simple terms, VSC looks at how much sky is visible from the centre of a window. The BRE guidance commonly referenced in practice says that daylighting may be adversely affected if the VSC at the centre of the window is below 27%, and it is less than 0.8 times its former value.

The planning goal is neighbourhood amenity and acceptability, especially in an urban context. It is not deciding private rights.

What Right to Light experts test (private legal injury)

Rights of light survey evidence is usually based on the Waldram methodology, which uses the concept of a sky factor (often under a uniform overcast sky) as a proxy for whether a room has enough natural light for ordinary use.

The well-known “50/50 rule” is a practitioner convention: a room is often treated as adequately lit if at least 50% of the room area at working plane height receives at least 0.2% sky factor.

Two important clarifications:

• The 50/50 approach is widely used, and the courts have discussed it, but it is not a strict rule of law. Courts have warned against applying it rigidly.
  
  
• Waldram is not measuring light intensity directly, it is measuring sky visibility used as a proxy for sufficiency. That is why it can produce different “answers” from planning daylight methods.
  
  

Why the results can diverge

Because the tests are looking at different things, it is entirely possible for a scheme to look “fine” in planning terms but still create a potential Right to Light problem.

A planning report might say the impact is acceptable in an urban area, even where the room-level effect is significant. Rights of light focuses on whether the remaining light is sufficient for ordinary use, backed by room-based modelling and the legal nuisance test, not planning policy.

A quick way to spot what you have been sent

If a developer sends you a “daylight report”, check the front page and methodology:

• If it references BRE guidance, VSC, NSL (no-sky line) or ADF, you are probably looking at a planning daylight and sunlight assessment.
  
  
• A Right to Light assessment will usually talk about Waldram, sky factor, 0.2% contour lines, and before/after room plans.
  
  

Neither document is “bad”. They just do different jobs. The mistake is treating a planning document as proof that private rights are safe.

What to do next

If you are concerned about loss of light, ask for a specific Rights of Light assessment, or get your own independent review based on:

• a reliable model of your property (including window positions and room layouts), and
  
  
• a reliable model of the proposed scheme, based on actual drawings.
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How Daylight Protect Can Help

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