Letters


We need more POE data Congratulations to CIBSE Journal for publishing the post-occupancy evaluation (POE) case study, and to Buro Happold for supplying properly organised data (September, page 35). The tabulated POE results for energy consumption per square metre on page 40 are particularly interesting, as they show the huge variation between individual dwellings, space heating and hot water. The data show the acute difficulties in (a) forecasting a particular client’s consumption when starting from scratch, and (b) setting up norms for regulatory design targets. One can quibble that the energy consumptions should be factored against the number of occupants, as kWh/sq m/person, and even against occupied hours per day as well; but allowing for these in the design stages is equally problematic and would probably alter the figures by concentrating most consumptions closer to the mean rather than by changing the overall spread. I accept that a single average figure has some use, but measured figures for a particular single building without supporting data are almost meaningless. My plea is therefore that predicted design


consumptions for all purposes, whether for Part L or for prediction of energy bills, should be calculated by rather more subtle methods than the currently accepted norms. For regulatory purposes, standardised occupant numbers and occupancy/ behaviour patterns must be used, and be a required input, so that arguments over figures submitted for regulatory approval and for energy certificate comparisons would largely disappear. Similarly the effects of occupancy patterns could be demonstrated more simply to a client and by an approved method. John Moss, MA, MCIBSE, CEng


Outliving its illuminance usefulness While your Lighting Roundtable discussed at some length potentials for reducing illumination levels, it failed to address the fundamental point that the way in which those levels are currently specified bears no sensible relationship to human assessment of lighting adequacy (CIBSE Journal, September, page 27). The schedules of visual task plane illuminance (which invariably is interpreted as horizontal workplane illuminance) require that ‘efficient’ lighting systems direct their output onto the floor, where a high proportion


24 CIBSE Journal October 2010


is absorbed without providing any visual effect. In a recently published paper (Lighting Research & Technology 2010, 42(1) 73-86) I have proposed a Perceived Adequacy of Illumination (PAI) criterion, which is satisfied by providing reflected light to the eye from surrounding room surfaces. I included an example of lighting design for PAI in which the illumination target is specified in terms of mean room surface exitance. This approach


see cars driving around without their lights on because the ambient lighting is higher and the driver isn’t aware? If we cut street lighting by 75% it would still be adequate. Stop light pollution and save energy. James Brown


Not the ‘voice for the profession’ I was not aware that comments made by me were going to appear in the August issue of CIBSE Journal (Letters, page 18). The comments were taken from a heavily- edited extract of a valedictory essay I wrote when I left the Engineering Council; the full version is available at http://bit.ly/aor12H So I was surprised to see Ian Brown’s


response in the September issue (Letters, page 20). Regarding his remarks, I would simply observe that the Engineering Council I led was not charged with acting as the ‘voice of the profession’, and it certainly did not ‘administer’ the 36 engineering institutions. Its sole task has been to run the licensing system to maintain and promote professional standards for the engineering profession. I believe that the Engineering Council has discharged this task well. Our involvement in speaking for the profession was largely the result of the vacuum I describe in my essay. Andrew Ramsay, Companion CIBSE Chief executive officer, Engineering Council, 2002-2010


inverts current notions of lighting efficiency and opens up opportunities for satisfying users’ expectations for spaces to appear adequately illuminated with very low lighting power density values. It is high time that we recognised that


visual task plane illuminance has outlived its usefulness for specifying illumination adequacy. Kit Cuttle, MA FCIBSE FIESANZ FIESNA FSLL Havelock North, New Zealand


Stop this street-light wastage More than 40 years ago I was engaged in the production and calibration of street lighting photometers and other photometers under the brand name EEL. It seemed that when the units of measurement changed from foot candles to lumens to lux, and lighting became a profession in its own right, the need for street lighting to be measured at very low levels went out of the window. How many times do you


Clarification: The way Ian Brown’s letter in the September issue was edited meant some readers may have been left with the impression that Andrew Ramsay had been chief executive of the Engineering Council (EC) for 35 years. To clarify, he joined the EC as director for engineering regulation in September 1997 and became its chief executive in April 2002, retiring on 31 July this year.


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