1 General

1. Lighting terms and concepts using the analogy of a sprinkler pipe

   

   1. Visible light is measured in lumens.

   2. One lumen of light flux spread over one square foot of area illuminates the area to one footcandle.

   3. The ratio of lumens/watts is called efficacy, a measure of energy efficiency.

   4. The incident angle of a light beam always equals the reflectance angle on a surface.

   5. The 1-1-1 Rule: When 1 lumen of light strikes 1SF of perfectly reflective area, 1 ? away, at right angles, then 1 lumen of output = 1 fc of incident light = 1 foot-lambert of reflected light.

2. Considerations in seeing

   1. Contrast between the object or area being viewed and its surroundings will help vision. Too little will wash out the object. Too much will create glare. Recommended maximum ratios:

      Task to adjacent area	3 to 1
      Task to remote dark surface	3 to 1
      Task to remote light surface	1 to 1
      Window to adjacent wall	20 to 1
      Task to general visual field	40 to 1
      Focal point: up to	100 to 1

   2. Brightness (How much light?). For recommended lighting levels, see d, below, or p. 574

   3. Size of that viewed. As the viewing task becomes smaller, the brightness needs to increase and vice versa.

   4. Time: As the view time is decreased, the brightness and contrast needs to increase and vice versa.

   5. Glare: Not...