Appendix E: CPTED (Crime Prevention through Environmental Design) Guideline http://cptedontario.ca

CPTED Notes on Safety and Security

• When creating lighting design, avoid poorly placed lights that create blind-spots for potential observers and miss critical areas. Ensure potential problem areas are well lit: pathways, stairs, entrances/exits, parking areas, ATMs, phone kiosks, mailboxes, bus stops, children’s play areas, recreation areas, pools, laundry rooms, storage areas, dumpster and recycling areas, etc.

• Avoid overly bright security lighting that creates blinding glare and/or deep shadows, hindering the view for potential observers. Eyes adapt to night lighting and have difficulty adjusting to severe lighting disparities.

  Using lower intensity lights often requires more fixtures.

• Use shielded or cut-off luminaires to control glare.

• Place lighting along pathways and other pedestrian use areas at proper heights for lighting the faces of the people in the space (and to identify the faces of potential attackers).

• Light areas where needed.

  i.e. parking spaces versus parking aisles.

Glare Standard

To avoid glare, the recommended maximum ratio of a light source to its surrounding area is 100:1. However, this cannot be applied to light sources at night since the surrounding is close to zero and any light source whatsoever exceeds this ratio. Glare is closely related to the brightness of a light source: technically, the luminance of the light source, expressed in candela per square metre (cd/m2).

Osterhaus [2] shows a luminance limit that depends on the angle from the viewer. Close to on-axis, the suggested limit is 582 cd/m2.Off axis by 45 degrees the limit is 2570 cd/m2.

Linney [3] suggests a luminance limit of 1500cd/m2. This threshold seems to correspond reasonably well to the threshold of discomfort for a light source viewed on-axis.

There are many other definitions of glare, some highly technical and difficult to apply without specialized equipment such as computer analysis of light levels and the geometry of the lighting arrangement.

The single-figure limit of 1500cd/m2 has the great virtue of simplicity and corresponds reasonably well to perceived glare. We recommend this level as the maximum allowed brightness of a visible light source.