Bryan Anstey

’I may have a passion for looking at the sea, whereas to some people it is a hateful sight, but access to light from the sky is essential to every normal person’s normal enjoyment of the use of rooms having apertures admitting light, and hence it is with access to sky visibility that the easement to light is essentially concerned.’

Anstey, B. 1963

I am grateful to David Bowden for asking my view on the work of Bryan Anstey. It has given me the opportunity to review my notes and commentary from more than ten years ago.

Many younger surveyors will have heard of John Anstey and/ or the company Anstey Horne but I suspect you have to be of a certain generation to remember that John Anstey’s father Bryan was one of the earlier surveyor practitioners in the field of rights to light.

I had the privilege of hearing one of John Anstey’s lectures at a Building Surveyors weekend briefing and asked my father about the subject. I then, in about 1983, obtained a copy of Bryan Anstey and Michael Chavasse’s book entitled The Right to Light first published in 1963, from the British Library.

I found the book fascinating and fully intended to put the content into practice as soon as the opportunity occurred. Needless to say, I had to learn all the basics including levelling surveys and how to use the Waldram Diagram and it wasn’t until the 1990’s that I had the opportunity to get involved in a case of my own.

However, by 2004 I was convinced that the basis of assessment of daylight was flawed and this led me to revisit the books that I had read as well as the published research material.

On reflection I can see several sections of Anstey’s book that rely heavily on the published works by Waldram but it is interesting to note that his commentary does indicate areas of consideration where alternative methods may be more appropriate.

Illuminance values

Anstey (1963; p42) provided two diagrams illustrating how the illumination in January does not fall below 500 Lumens between 9.30 a.m. and 2.30 p.m., whereas in December the corresponding times would be 10 a.m. and 2.00 p.m. He also noted that there was a rapid jump in November and February and that by April the period during which 500 Lumens could be received from the sky had gone up to 11 hours and the maximum intensity had risen by more than three times that of December.

The value of sky brightness by angle of altitude was summarised by Anstey in a small table (p44) which predicted a sky brightness factor at 5 degrees altitude of 0.5 and at 80 degrees altitude of 1.27 which is similar to the values predicted for a CIE overcast sky which predicts that the luminance at the zenith will be three times that at the horizon. It has been observed that, in ‘Rights to Light’ cases, this variation from zenith to horizon could be important in that different patches of sky whilst of the same area, would offer different amounts of illuminance and that this might be significant.

He cited the work by Dr J.W.T. Walsh who came to the conclusion that for angles between 25 degrees and 65 degrees the difference does not exceed 20% and that as this range of angles covers the majority of cases (?) likely to be met in practice that it may be concluded that the uniform sky model was appropriate. Anstey then commented that “whilst one may agree that the ‘majority’ of cases may fall within this view… sight must not be lost of the necessity to use other methods if a court is to be convinced in a case where different circumstances apply.”

Anstey then goes on to state that “by definition” the sky factor is calculated with a sky of assumed uniform luminance. In my view it is unclear from where this definition derives. However, he does point out that even the CIE sky is only approximate and only for the overcast sky.

On page 49 Anstey writes that “It may well be that a new study, validating or refuting the soundness of the 50-50 rule based on the 0.2% sky factor contour needs to be made for the guidance of the courts but that in the absence of challenge the findings of International Commission on Illumination (1932) should be followed.

He then listed three resolutions:

1.      The use of contour lines be adopted .... in all questions.

2.      Table height 85 cms

3.      Less than 0.2% daylight inadequate for work involving visual discrimination.

Anstey then warns that there are peculiar and special dispositions which might result in little movement of the contour but result in a quantitative diminution of light which might be an actionable injury. Thereby inviting challenge in the event of any special case.

I have found no evidence that Bryan Anstey actually undertook any scientific research into either adequacy or measurement, but he does state that “it is quite easy to show that a book can be read, and writing can be undertaken by the light of a single candle placed a distance of a foot or so from the work”.

Having undertaken some controlled research into this subject area I can state with some certainty that anyone trying to work by the light of a single candle for any length of time will suffer eye strain although the length of time appears to vary with age. i.e. the older you get the more light you tend to need for comfortable working conditions.

Despite the critique I am indebted to both Anstey’s father and son and of course to my own father for setting me on a course towards this point where I realise how much more there is to learn.

Bibliography

Anstey, B. and Chavasse, M., 1963. The Right to Light. London: The Estates Gazette: