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The Ordinary Notions of Mankind: The Research Basis of Waldram ’ s 0.2% Sky Factor. Paul Chynoweth. The Right to Light…. An entitlement to “sufficient light” for the comfortable use and occupation of a dwelling house, or for the beneficial

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slide1

The Ordinary Notions of Mankind:

The Research Basis of Waldram’s

0.2% Sky Factor

Paul Chynoweth

slide2

The Right to Light…..

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.

…..and the role of the expert witness

slide3

Sufficient light

according to the ordinary notions

of mankind?

slide4

Sufficient light

according to the ordinary notions

of mankind?

slide5

Sufficient light

according to the ordinary notions

of mankind?

slide6

Sufficient light

according to the ordinary notions

of mankind?

slide7

500 lux

150 lux

Illuminances recommended for general offices since 1930

Boyce, Human Factors in Lighting, 2003

(after Mills & Borg, 1999)

slide9

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).
slide11

1.

“it is more or less confirmed by the data of existing conditions

in factories contained in the Home Office Report” (Waldram 1923).

“This assumption…received a valuable and welcome confirmation”

from the Illuminating Engineering Society’s Report on the Daylight

Illumination of Schools (Waldram 1925).

2.

3.

“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).

Official support for the “grumble point”?

slide12

Report on the Daylight Illumination of Schools (1914)

(Waldram was one of the six investigators)

Recommendation

  • Minimum acceptable illuminance at the worst lit
  • desk should be 0.5% SF.

CIBSE guidance 1987: 2% DFmin

5% DFav

slide13

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)

Home Office Report on Existing Lighting Conditions

in Factories (1915)

“The extremely low value [of the 0.25% figure] demonstrates

the comparative inefficiency of side lighting for floor or

general illumination.” (Report, p. 40)

slide14

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.
slide15

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”.

slide16

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.

slide17

Post War Building Studies

No. 12 - The Lighting of Buildings (1944)

Kitchens: 2% DFmin

Living rooms: 1% DFmin

Bedrooms: 0.5% DFmin

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

Offices: 2% DFmin(at reference point 12 feet from window)

slide18

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.
slide19

Reference

Chynoweth, P., ‘Progressing the rights to light debate, part 2: the grumble

point revisited’, Structural Survey, Vol. 23, No. 4, 2005, pp. 251-264.

Available from:

www.rightstolight.co.uk

www.rightstolight.com