Discussion Six: Michael and Peter

Michael Kent (a researcher at the Berkeley Education Alliance for Research in Singapore) interviewed Peter Tregenza, on 15th December 2018. 

Michael (MGK): Thank you for having this discussion with me today Peter. To get started, I would like to talk about some of your current activities. I understand that you have been retired from academic life for a period of time now. I was wondering if you spend time often thinking about research and if so, how does this differ from when you were working in the university environment.

Peter (PRT): I am eighty years old now and have been retired for nearly fifteen years. Looking back I can’t discern a clear boundary between employment and retirement. I think that if you have spent a working lifetime immersed in a subject, and enjoying it, there is no off-switch available. There are always new questions and new techniques.


But something very significant happens on retirement: you stop getting paid. In addition you find that resources that you have relied of all through your working career are suddenly changed: you lose easy access to laboratories and technician support; you miss the colleagues who make useful suggestions over coffee; above all, you lose contact with your peers in other institutions and other countries because the costs of attending national meetings and international conferences are too great.


So research tends to be different after retirement. It is personal rather than teamwork, theoretical rather the experimental. But, you can do what you like. You might have had considerable freedom during your career to choose research subjects but there were always obligations. When you are retired you can spend six months working at some fascinating theoretical and possibly useless topic and nobody will say that you should turn it into a paper before the next semester.

MGK: Excellent. I know in your academic career that you are largely known for your work in daylighting and lighting research in buildings. But now you have had some time to reflect back, would you have liked to have focussed on any other areas of building design other than on illumination?

PRT: In my final year as an architecture student I was given some advice by my tutor, Professor J H Napper, a wise and very kind man to whom I am indebted for much. He said, “Try to follow two or three different areas of research at the moment: you can’t foresee how useful a particular subject might be twenty years from now. You might also find that different areas of knowledge, however unrelated they seem to be, often illuminate each other.”
That resonated with me. I was struggling with the question, “What is the optimum form of a large building, the overall shape that gives the ‘best value’ (however you choose to define this)”. Two of the many things that determine a large building’s form seemed especially interesting: the first was need for daylighting, the second was the circulation of people within a building. These became the topics of my final architecture dissertation and my Master’s and PhD theses. 


The school of architecture that I went to was in King’s College of Durham University (now Newcastle University). Only a few years before I arrived in 1957 it had been a Beaux-Arts school and the curriculum reflected that, so I got a very good education in architectural history and theory. And I became a crusader for modern architecture. After graduating I worked in Professor Napper’s practice, mainly on large-scale housing, and then I was lucky enough to get a Commonwealth scholarship to Sydney University where I took a master’s degree in architectural science, I would have liked to stay in Sydney – I was offered a lectureship – but under the terms of the scholarship I had to return to the UK.

MGK: On your return from Sydney you went to Nottingham University.  What was your work there?

PRT: For the first three years my appointment was a half-time lectureship, the other half in architectural practice. I was a studio teacher for much of the next twenty years, a part of the job I enjoyed greatly. I lectured in a variety of subjects at first.  (This happens when you are the youngest in the department and there are courses that nobody else would wanted to teach.)  I ran an art club, which met in the evenings. As time went by I specialised in environmental design, especially lighting. I was promoted in stages and became a Reader. In 1988 the head of department left, and I acted as head for a year, I then moved to Sheffield University.

MGK: Was it a difficult decision to leave Nottingham?

PRT: Yes. Nottingham was a very good school of architecture and with some excellent scholars on the staff. But I had been at Nottingham for quarter of a century and it was the time to make a change in my career.

MGK: May we talk about your research, especially your PhD?

PRT: I had become interested in the movement of people in buildings, particular when there is intense use, such as in a London underground station or an airport terminal. I wrote my PhD while I was a member of staff at Nottingham. The subject was the application of probability theory to the movement of people. I was lucky, I had two very supportive Academic Advisors: one was Professor Rex Coates, a highly respected civil engineer, the other was Clive Granger who went on to win a Nobel Prize for economics

MGK: What was it like to have a future Nobel Prize winner as an academic advisor, did this influence or inspire your research in anyway?

PRT: Rex Coates was my primary advisor. Clive Granger gave me criticism on things I had written; he was extraordinarily busy and I was lucky to have him at all. Both were inspirational to me. I felt privileged for the care they gave when I was a young lecturer and they were senior professors. Nottingham University has since recognised the international renown of both men by naming buildings after them.

MGK: In Nottingham, you managed to write two of your most renowned research articles, the daylight coefficients and subdivision of the sky hemisphere for luminance measurements. What inspired you to write these at that time?

PRT: It’s odd. When these two papers were first published they attracted little attention because they were technical papers on a topic which interested very few researchers. Now, thirty years later, they are being cited at a rate about ten time greater than that during their first few years.


I had been working simultaneously on lighting and on the movement of people, but I became more and more interested in lighting, particularly daylight. There didn’t seem to be any answer to questions like “Is the natural variation of daylight a good thing or just a nuisance?” and “How accurately can daylight be predicted?” I searched the literature and did not find anything like a comprehensive answer to several fundamental questions, although there had been some excellent research. So in Nottingham I set up a measuring station which recorded sun and sky illuminances, simultaneous illuminances in a daylit room and in scale models under the real sky. A lot of data were collected.


In analysis I tried to picture how a daylit room actually behaves. Technically the central question was, ”How good is the Daylight Factor as a predictor of the ratio of interior to exterior illuminance when the sky luminance distribution varies? I found that it was not a good predictor.  I concluded that the daylight factor was simplistic and that the relative sky brightness pattern should always be a component in daylight calculations. I realise now that I was wrong on both points: the real answers are more complex and even more interesting.
I looked at the underlying mathematics that modelled daylight and realised that there were two distinct and separable sets of parameters in the fundamental equation; those defining the sky and those describing the built form .This should make it possible to characterise the built form effects just once, at the start of a calculation, instead of a large number of repetitions as in the conventional methods. 


The subdivision of the sky is an entertaining problem. You begin by asking how the surface of a hemispherical dome can be subdivided into 100 or so equal areas, and add the constraint that they should be defined by a sequence efficiently recorded by a sky scanner. The scanner rotates, measuring luminances at a circle of points at a fixed elevation, then steps up to measure a circles of points at higher elevations.


I wrote computer programs that projected patterns of patches onto a sphere and calculated the proportion of sphere area each pattern produced. I found one that was very interesting, with three-way symmetry and very good coverage. This was adopted by the CIE for sky luminance scanning, It has been used widely also in sky luminance modelling.


I went on to investigate different alternative ways of modelling daylight. In my PhD I had treated the arrival of people at lift lobbies as a random process. It was interesting to find that the same mathematics could be used to describe the spacing of clouds being blown across the sky. I published several papers on daylight theory and measurement.  I became involved in the CIE’s international daylight measurement project and as deputy director of CIE Division 3 I coordinated and wrote technical specifications for the project. This was a completely enjoyable time with enthusiasm and cooperation between organisations in different countries.

MGK: I noticed that in some of your research articles that you have qualifications from the RIBA and CIBSE. This is an amazing accomplishment since not may carry qualifications in both architecture and engineering. Do you think having knowledge in both gives you a different perspective in your research?

PRT: I am an engineer as well as an architect. I am proud of this; my father was an engineer and so is my eldest son. But I did not plan it. In the early 1970s the Illuminating Engineering Society and the Institution of Heating and Ventilation Engineers merged and became a chartered institution. Existing members had to be assessed for designation as a chartered engineer. Some senior lighting designers were excluded, and there was backlash to the changes, but I was fortunate: my master’s degree, my PhD and some Open University courses I had taken in mathematics were deemed to satisfy the requirements for engineering training. I had also worked for a time in the office of a consultant engineering firm.


I do find it helpful to be able to see research from a differing viewpoint.

MGK: I completely understand. While you were teaching at academia, were you able to travel to broaden your horizons and visit other academic institutions?

PRT: Through the British Council we made links with overseas schools of architecture. Staff from overseas schools would spend a year or a semester with us in Nottingham and we were able to go to them. I went to China, Singapore, Chile, Australia, New Zealand, Brazil. In those schools of architecture there were different values and different ways of teaching but in essence they felt just the same. There are characteristics of an architecture school that seem to be universal – the same grumbles in the staffroom, the same pleasures and disappointments when teaching over the drawing board.

MGK: That is really incredible. Over the span of your career I have noticed that you have examined many PhD theses – in particular there are some from now notable professors that are working in the field of daylighting that you were the examiner – do you ever use a set of criteria of your own to examine the judge the quality of the thesis?

PRT: I try not to. Ideally the criteria of a PhD would be fundamentally the same throughout the world. In many universities a PhD examiner has to answer three questions: Is the dissertation and the research described in it the candidates own work? Does the candidate possess broad knowledge of the subject and technical competence at a professional level? Does the outcome of the research advance knowledge of the subject?

MGK: What advice would you give to a new PhD student just starting their doctorate programme?

PRT: Decide what of sort of work activity that you both enjoy and do well: working with people? With computers? In a laboratory? Studying historical documents? And so on. (Choose carefully because you might be doing it for the next three years). Discuss this with your supervisor and work with him or her to define a topic that requires that type of work. Then get really enthusiastic about it.

MGK: You appear to have worked for some years on people’s needs and subjective aspects of daylighting, what areas in particular were you most interested in?

PRT: I have worked on most aspects of daylight. At first, being an architecture student I was interested in how daylight affected building design. Then I spent several years looking at quantification – measuring daylight in different sorts of buildings, wondering how to describe the different types of sky from the point of view of daylight calculation. Daylight coefficients, the paper written with Isobel Waters of Oxford Brookes University, came out of this.


I became chairman of the British standards committee responsible for codes of practice in lighting. I felt that I needed to know more about peoples’ needs and preferences for daylight, and on discomfort from daylight. This became a new focus if research, and there were some valuable results. For instance, Nuanwan Tuaycharoen, a PhD student working with me, showed that people found a window less glaring when it overlooked an interesting view than when it overlooked an unattractive area that was photometrically similar.

MGK: Among the many publications in your career, which ones are you the most proud of?

PRT: I enjoyed writing them but all but some have been more successful than others. I was pleased with the papers on modelling the cloudy sky, looking at clouds and the inter-reflection between them. But nobody really noticed those.

MGK: When you were planning to submit a particular article, were there any journals in particular that you would target?

PRT: Lighting Research and Technology would be my normal choice, it’s the leading journal internationally. It started about a century ago as Transactions of the Illuminating Engineering Society. At first it was mainly a record of meetings. Over the last decade it has become a very good journal indeed, mainly due to the work of Peter Boyce as technical editor. He is now editor in chief.

MGK: How long it take you to write a paper?

PRT: It depends on the topic, of course. For a mainstream scholarly article I find that I produce text at a rate equivalent to about one finished printed page daily. I tend to hang onto papers for weeks or months waiting for the mistakes to bubble out.

MGK:  At one point, you were the chairman of LR&T. Is this correct?

PRT: Yes, I was the chairman of the editorial board. This has the duty of setting policy and guiding the journal.

MGK: Were you ever interested in moving outside daylighting into other areas? You had one paper where you worked on acoustics. Do you have a special interest in look at noise and sound in buildings?

PRT: It’s a really interesting field. But, all I did was explore whether any of the algorithms we use for predicting lighting performance could be used for acoustics. If you just add an additional parameter for wavelength, could you simulate the wave structure? I didn’t continue with this work because I found it was getting too far away from the lighting algorithms.

MGK: I can completely understand that. If we go back to daylighting and look at this subject throughout the course of your career, where do you see the direction this area going in the future?

PRT: The topic that is most incomplete is criteria for daylighting. Research has focussed on numbers rather than look for underlying reasons.

MGK: Do you think that health-based matrices that are link with to lighting will also emerge from this?

PRT:  Yes. The crucial fact about daylighting criteria is that it is not the quantity of light that is important, it is the information that it carries. For example, daylighting is valued for what it tells you about the room you are in and about what is happening outside. Knowing how daylight illuminance varies can be more important than knowing the absolute level. Moreover, in a cloudy climate like England’s, daylight illuminance can be described only in terms of probability.

MGK: In your opinion, how important is it for new students or new researchers to learn statistics or other forms of analysis used in their research?

PRT: Statistics are crucial if your project involves logical or numerical hypotheses in conditions of uncertainty, and a surprising number of projects reduce to just that. It is not calculations that are important, a machine can do those. You have got to answer the question “What is actually happening here?” Being able to do that is not easy: the simpler you try to put it, the harder it is to formulate.

MGK: I understand. For you, since you started your career, how has academia changed and does this introduce different challenges for early career researchers?

PRT: There have been three huge changes during my career:  the introduction of mandatory research assessments, the availability of computers and the growth of postgraduate student numbers in schools of architecture. I would like to talk about these for hours, but that is for another day. Enough to say that in my view the first has been almost a complete disaster; the second has been, for me, essential – I used computers in the early 1960’s and they have been my main tool for more than half a century; the third, the growth in student numbers brings opportunities for some but hardship for others.
The post-doc situation is a difficult now and has been difficult for nearly a decade. It is scandalous that men and women educated to a level of a doctorate should find it difficult to get long-term employment.

MGK: Looking at your career overall, if you could go back would you change anything?  Is there anywhere you would like to visit but not had the opportunity?

PRT:  I would do the same again. You can plan a career but unexpected opportunities arise, almost randomly. If I were forty years younger I would seize some new opportunities and to revisit some earlier ones. Wherever I have travelled I have met people of great ability, and the greatest pleasure of the kind of career that I have had is that these people become your friends.

MGK: That is absolutely brilliant. I think now that would be our last question but if you have any other questions you would like to discuss, please let me know before conclude here. But as always my discussion with you has been inspiring and thank you for this opportunity.

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