The Ordinary Notions of Mankind: The Research Basis of Waldram ’ s 0.2% Sky Factor Paul Chynoweth

An entitlement to “sufficient light” for the comfortable use and occupation of a dwelling house, or for the beneficial use and occupation of business premises, “according to the ordinary notions of mankind”. Lord Lindley, Colls v Home & Colonial Stores [1904] AC 179, HL. The Right to Light….. …..and the role of the expert witness

Sufficient light according to the ordinary notions of mankind?

Sufficient light according to the ordinary notions of mankind?

Sufficient light according to the ordinary notions of mankind?

Sufficient light according to the ordinary notions of mankind?

Illuminances recommended for general offices since 1930 Boyce, Human Factors in Lighting, 2003 (after Mills & Borg, 1999) 500 lux 150 lux

Origins of Waldram’s 0.2% “grumble point”?

“an assumption which the author has invariably applied in ancient light disputes for many years” (Waldram 1925). “It has no official status and has not been investigated by the NPL” (Waldram 1923). “a rough working rule would be that all parts of a room should have a minimum illumination of 1candle-foot” (Waldram 1909). Based on the assumed sky luminance of 1000 ft-candles, proposed a grumble point of 0.1% (Waldram 1909). Later changed to 0.2% in line with 500 ft-candle standard uniform sky. Proposed 0.2% minimum “at the worst-lighted working point in the room” (Charles Semon & Co v Bradford Corpn 1922).

Official support for the “grumble point”?

“it is more or less confirmed by the data of existing conditions in factories contained in the Home Office Report” (Waldram 1923). 1. “This assumption…received a valuable and welcome confirmation” from the Illuminating Engineering Society’s Report on the Daylight Illumination of Schools (Waldram 1925). 2. “These values may seem a little low according to text-books on artificial lighting, but in view of comprehensive tests in government offices, I do not expect to find the original standards varied” (Waldram 1928). 3.

Report on the Daylight Illumination of Schools (1914) Recommendation Minimum acceptable illuminance at the worst lit desk should be 0.5% SF. (Waldram was one of the six investigators) CIBSE guidance 1987: 2% DF min 5% DF av

Home Office Report on Existing Lighting Conditions in Factories (1915) Mean Survey Results 0.25% DF (Factories with side lighting only) 1.8% DF (Factories with combined roof & side lighting) 2.3% DF (Factories with roof lighting) “The extremely low value [of the 0.25% figure] demonstrates the comparative inefficiency of side lighting for floor or general illumination.” (Report, p. 40)

The Daylight Illumination Required in Offices (1931) Recommendation 0.2% SF should be taken as the threshold of adequate daylight for clerical work. Impartiality of the investigations? Dismissed as “much too low” by a subsequent investigation into lighting in government offices in Recommended a minimum of 5 ft-candles (50 lux) for clerical work.

CIE Resolution, Cambridge, 1931 “That at all parts of interiors where the daylight factor at table height (85 cm) is less than 0.2%, the daylight shall be regarded as inadequate for work involving visual discrimination”.

CIE Resolution, Cambridge, 1931 “That at all parts of interiors where the daylight factor at table height (85 cm) is less than 0.2%, the daylight shall be regarded as definitely inadequate for work involving visual discrimination. This is not recommended as a standard of adequate intensity of illumination.” Compare with the summary of this resolution in: Anstey, B. The Right to Light, Estates Gazette 1963, p. 38.

Post War Building Studies No The Lighting of Buildings (1944) No The Lighting of Office Buildings (1952) Kitchens:2% DF min Living rooms:1% DF min Bedrooms:0.5% DF min Offices:2% DF min (at reference point 12 feet from window)

Some concluding thoughts Percy Waldram’s central role in promoting the 0.2% / 1 ft-candle threshold. Generally unsupported by independent research from the 1920s & 30s. Inconsistent with contemporary guidance (CIBSE / BS). Ignores the distinction between task lighting (the subject of the right to light) and general room lighting. Effectively based on the position of the no-sky line? (an indication of general room lighting). Focuses on the internal, rather than the external, environment. 45 degree rule, 25 degree rule and the vertical sky component. Significance of human perceptions.

Reference Chynoweth, P., ‘Progressing the rights to light debate, part 2: the grumble point revisited’, Structural Survey, Vol. 23, No. 4, 2005, pp Available from: