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 useand occupation of a dwelling house, or for the beneficialuse and occupation of business premises, “according to theordinary 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 lightaccording to the ordinary notionsof mankind?

CIBSE / BS General Offices 2% DFmin 5 DFav Kitchens 0.6% DFmin 2 DFav Living rooms 0.5% DFmin 1.5 DFav

GENERAL ROOM LIGHTING Bedrooms 0.3% DFmin 1 DFav

Sufficient lightaccording to the ordinary notionsof mankind?

CIBSE / BS General Offices 2% DFmin 5 DFav Kitchens 0.6% DFmin 2 DFav Living rooms 0.5% DFmin 1.5 DFav

GENERAL ROOM LIGHTING Bedrooms 0.3% DFmin 1 DFav

WALDRAM 0.2% SF50% 0.2% SF50%+ 0.2% SF50%+ 0.2% SF50%-

Sufficient lightaccording to the ordinary notionsof mankind?

CIBSE / BS General Offices 2% DFmin 5 DFav Kitchens 0.6% DFmin 2 DFav Living rooms 0.5% DFmin 1.5 DFav

GENERAL ROOM LIGHTING Bedrooms 0.3% DFmin 1 DFav

WALDRAM 0.2% SF50% 0.2% SF50%+ 0.2% SF50%+ 0.2% SF50%-

General Offices

500 lux

TASK LIGHTING

Kitchens

500 lux

Sufficient lightaccording to the ordinary notionsof mankind?

CIBSE / BS General Offices 2% DFmin 5 DFav Kitchens 0.6% DFmin 2 DFav Living rooms 0.5% DFmin 1.5 DFav

GENERAL ROOM LIGHTING Bedrooms 0.3% DFmin 1 DFav

WALDRAM 0.2% SF50% 0.2% SF50%+ 0.2% SF50%+ 0.2% SF50%-

General Offices

500 lux

TASK LIGHTING

Kitchens

500 lux

10 lux (1 foot candle)

10 lux (1 foot candle)

Illuminances recommended for general offices since 1930Boyce, Human Factors in Lighting, 2003

(after Mills & Borg, 1999)

500 lux

150 lux

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

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”?

Official support for the “grumble point”?

“it is more or less confirmed by the data of existing conditionsin 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-bookson artificial lighting, but in view of comprehensive tests ingovernment offices, I do not expect to find the originalstandards 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% DFmin 5% DFav

Home Office Report on Existing Lighting Conditionsin 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] demonstratesthe comparative inefficiency of side lighting for floor orgeneral 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 1937. 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 tableheight (85 cm) is less than 0.2%, the daylight shall be regardedas inadequate for work involving visual discrimination”.

CIE Resolution, Cambridge, 1931

“That at all parts of interiors where the daylight factor at tableheight (85 cm) is less than 0.2%, the daylight shall be regardedas definitely inadequate for work involving visual discrimination.This is not recommended as a standard of adequate intensityof 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. 12 - The Lighting of Buildings (1944)

No. 30 - The Lighting of Office Buildings (1952)

Kitchens: 2% DFmin

Living rooms: 1% DFmin

Bedrooms: 0.5% DFmin

Offices: 2% DFmin (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 grumblepoint revisited’, Structural Survey, Vol. 23, No. 4, 2005, pp. 251-264.

Available from:

www.rightstolight.co.uk

www.rightstolight.com