UFC 3 -520-01
June 10, 2002
DETERMINING LIGHT QUANTITY REQUIREMENTS.
Basic Requirement. Verify the quantity of illumination meets the
requirements of the visual tasks being performed, or other requirements stated in this
manual. Unless specifically stated otherwise, determine the appropriate illumination
according to the IESNA Illuminance Selection Procedure from the IESNA Lighting
Measurement of Illumination. Unless specifically stated otherwise, the
illumination requirements defined in this section are for horizontal illumination measured
in the horizontal plane at the task, or for general illumination in a plane 762 millimeters
(30 inches) above the floor.
Lighting Level at the Task. The IESNA Lighting Handbook lists appropriate
illumination levels in footcandles and lux for various visual tasks. Design lighting to
provide illumination within this range at each task. Light levels that are higher might be
acceptable, but consistent or significant overlighting is not efficient and should be
avoided. In this manual, specific light levels are specified for particular applications and
take precedence over IESNA recommendations.
General or Ambient Illumination. Illumination levels in the area surrounding
the task can be as high as the task light levels or as low as 1/3 of the task light levels.
Significantly higher ambient to task light levels (>1/1) can create too much contrast,
which can cause discomfort and use energy unnecessarily. Lower ambient to task light
levels (<1/3) can also create uncomfortable contrast.
Illumination in Adjacent Areas. As part of the selection of illumination
levels, take into account the light in adjacent spaces to minimize transient adaptation,
which is the process of the human eye adjusting to differences in light levels when
moving from one space to another. Typical transient adaptation situations that cause
visual difficulties include entering a very dark room when coming from a brightly lit
environment such as daylight. When the difference is greater than 1,000:1, the eye will
be momentarily blinded. If the difference is 10,000:1, such as entering a darkened
theater from outdoors, the eye will be blinded for several minutes while the eye adjusts.
Adjustments of 100:1 or less do not cause significant temporary blindness.
DETERMINING LIGHT QUALITY REQUIREMENTS.
Flicker and Stroboscopy.
F-4.1.1 For indoor lighting, minimize light source flicker. This can be accomplished
using electronic high frequency ballasts for fluorescent and compact fluorescent lamps,
and through the three-phase rotation of high-intensity discharge (HID) light sources
(refer to Figure F -1).