David PalmerDavid was born in 1933 in North London and was educated at Christ's College in Finchley. He became an undergraduate at Imperial College, graduating in physics, where he come to the notice of Professor W D Wright who took him on as a PhD student to work on stereoscopic vision. He gained his doctorate in 1958 and joined the National Physical Laboratory where he met W.S. Stiles and worked on the large field colour matching functions of Stiles and Burch. He started work with Brian Crawford on colour rendering experiments, a collaboration that developed into a friendship and lasted until Crawford died.

In 1967 he moved to Robert Weale's department at the Institute of Ophthalmology where he was primarily concerned with mesopic and scotopic vision. At various times David chaired NIC technical committees on colour rendering and on Mesopic Photometry and was also Chairman of the Colour Group

It is, perhaps, for his mesopic photometric model that David is best known. He worked out a way for specifying mesopic photometry which was simple and is still of importance. His experiments were to match monochromatic lights with white light of colour temperature 2042°K. The remarkable thing was that the size of the matching fields was 5, 10, 15 or even 45 degrees and the range of luminance was four, five or even six log units. When a match had been made he calculated the photopic and the scotopic luminance and plotted one against the other in what he called P/S plots. He got an interesting set of curves with a line parallel to the S axis at high luminance which curved over to become a line parallel to the P axis at low levels. There was obviously a changeover of "driving mechanism" between photopic and scotopic conditions in the mesopic range. He showed an empirical expression could be used to specifiy the mesopic luminance, L(S,P), thus:

L(S,P) = (M.S + P2)/(M + P)  where M is a parameter with the dimensions of luminance.

David Palmer is also remembered for his work on colour rendering. He started on this at the NPL and he later joined a team of experts, some still members of the Colour Group, to carry out a series of experiments to assess the colour rendering tolerances of fluorescent lamps. The first result was a paper called Colour Rendering Tolerances in the CIE System. The experiments were quite heroic and the subsequent calculations were extensive. The tolerances were much greater than expected and it was not possible to derive a general colour rendering index - it seemed that more work was required.

The team went on to produce a whole series of important papers concerned with colour rendering in hospitals. The NHS wanted the most light for the least money and was disposed to use fluorescent lamps but some of these distorted the colours of patients. Papers from the team appeared regularly through the eighties but the last of the series was published in Lighting Research and Technology in 1991 and described a number of tests with wards and clinic rooms lit by various fluorescent lamps. The results involved evaluation by staff. The conclusions were that fluorescent lamps with a correlated colour temperature of around 4000K were satisfactory and that some of the more efficient lamps with narrow band emission phosphors were as good as the older lamps. The team were eventually awarded Walsh Western Bronze Medal of the Chartered Institution of Building Services Engineers.

Eventually David retired from the Institute of Ophthalmology for lab space at the University of Westminster. He worked on a number of topics, especially on the effectiveness of sunglasses. The first problem was: do the glasses cut down the light sufficiently and keep out the ultraviolet radiation. Then there was the problem that coloured lenses might distort colour perception and especially the detection of coloured light road signals.

David continued to work on spectral visual sensitivity problems. He measured the scotopic luminosity function of a number of protanopes and showed their sensitivity was about 0.5 log units below the CIE V'(λ) at long wavelengths, as one might expect if the scotopic function is the result of combined rod and cone activity. He also re-analysed the scotopic luminosity function data of Crawford's 1949 paper by fitting the Dartnall nomogram to the data of each individual. The wavelength of peak sensitivity varied markedly as did the individual curve shapes, some subjects having profiles much narrower than the Dartnall nomogram. These differences could not be completely explained by pre-retinal pigmentation or by linear additions of one type of rod response with various cone responses.

The last four or five years left to David were spent making his own set of measurements to extend those of Crawford to investigate the individual differences in scotopic response. Allowance had to be made for pre-retinal absorbing pigment so it was necessary to measure macular pigment. Light emitting diodes made good pseudomonochromatic sources for constructing a macular pigment measuring instrument using heterochromatic flicker photometry. Several designs with ever reducing optical complexity were constructed and this lead to a design that is now in use across Europe. It was whilst calibrating one of these instruments that David was taken ill - after this he was not able to do any more work.

David was always careful to do proper science and to help others to do good science too. In his later years he was appalled by the way successive Governments treated science, scientists and those being educated in science. He devoted much time to ways to improve this and fully supported the programmes of, for example, the Royal Institution and the Institute of Physics, to bring an understanding of science to the general population. He left substantial sums to several organisations to contiue this work and one beneficiary was the Colour Group and this has been used to endow an annual lecture and a set of awards, and to support a teaching fellows to work in schools.

David Palmer was a past chairman of the Colour Group and his interests and those of the Group were well matched. As Michael Pointer, a former Chairman of the Group, has said, David was a polymath with a wide range of talents and interests. All who knew David held him and his work in high regard. We members of the scientific community miss him more than perhaps we care to admit.

John Mellerio

Shortened version of a lecture by John Mellerio given to introduce the first Palmer Lecture in 2004 is available here in PowerPoint.

DATE 10 Jan 2015