4.3 Lighting

In addition to lighting the roadway for required visibility, designers should consider the illumination of significant structures, such as bridges and walls, to provide clarity and interest at night as shown in
Figure 4-19
. Lighting for visual emphasis typically occurs within Urban and Suburban contexts, though major Rural and Rural Town interchanges or intersections may also benefit from increased contrast and visibility. Illuminated, backlit, or directly lit elements along the highway improve the overall perception of the highway corridor.
Aesthetic lighting may provide visual effect and enhance the following features:
  • Roadway Structures;
    • Bridges
    • Walls and Wall Textures
  • Landscape Elements; and
    • Sitework and Hardscape
    • Trees
  • Artistic Elements
    • Bas-Relief
    • Decorative Metalwork
    • Sculptures
Aesthetic Bridge Lighting, IH 35 Bridge at Brazos River, Waco

4.3.1 General Requirements

Aesthetic lighting must be designed and installed in a way that will not distract drivers or create a safety hazard according to the following guidelines:
  • The feature may not contain or be illuminated by flashing, intermittent, or moving lights, including any type of screen using animated or scrolling displays.
  • Luminaires must be shielded, directed, and positioned to prevent beams or rays of light from being directed at any portion of the traveled ways of a regulated highway.
  • The lighting may not be of such intensity or brilliance as to cause vision impairment of a driver of any motor vehicle on a regulated highway, or otherwise interfere with the driver's operation of a motor vehicle.
  • Illuminance levels shall conform to the recommendations in Chapter 26, Lighting for Exteriors, from the
    Illuminating Engineering Society (IES) Lighting Handbook, 10th Edition.
  • Lighting features that are not crash worthy must be located outside the roadway clear zone or protected by a TxDOT approved crash barrier.
  • The lighting may not simulate, resemble, obscure, or interfere with the effectiveness of an official traffic sign, device, or signal.
  • When possible, cutoff luminaires should be used to minimize light pollution as called for in
    Texas Health and Safety Code Chapter 425, Regulation of Certain Outdoor Lighting
    .
  • For direct view sources like LED or neon, the aesthetic lighting should not exceed 0.3 footcandles over ambient lighting levels when measured according to the International Sign Association's
    Recommended Night-time Brightness Levels for On-Premises Electronic Message Centers (EMCs)
    .
  • For lighting designed to change appearance over time, the minimum length of time between changes of scene shall be either:
    • At least eight seconds; or
    • Calculated by the formula: Sight distance to lit area (ft) / Speed limit (ft/sec) = Minimum display duration (sec).
  • Lighting systems and Illumination levels should meet and conform with the applicable requirements of AASHTO, IES, the
    National Electrical Code
    , BUG (Backlight, Uplight, Glare) ratings, the TxDOT
    Highway Illumination Manual
    , and other standards as deemed appropriate by the TxDOT District Engineer.

4.3.2 Light Sources

LED fixtures are the standard for highway lighting and should be used for aesthetic lighting as well. The color standard for highway fixtures is 4000K, though slightly warmer colors may be suitable for the landscape, ranging between 2700K - 3500K. Other considerations for LED aesthetic lighting in the landscape are as follows:
  • LED fixtures require drivers to operate. Some are contained within the luminaire, but others are not. Ensure the design includes all components, connections, and necessary space to perform effectively.
  • If specifying LED displays with color-changing arrays, include strong security features to prevent unauthorized operation of the lights (manually and/or digitally).

4.3.3 Posts and Luminaires

Choose the style of posts and luminaires based on practical requirements. First, consider height clearances, single or double arm, post arm reach, the inclusion of banner fixtures (if warranted), etc. After these have been considered, then consider the character of the space. See
Figure 4-20
.
  • The post and the luminaire should complement the style and character of the surroundings. For example, a Contemporary or Post-modern space would be enhanced with fixtures that fit within the design. The
    Texas Historical Commission
    should be consulted for guidance on choosing light fixtures for historic districts located within the TxDOT ROW.
  • Widely spaced posts read as individual objects within the landscape; closely spaced posts tend to read as defining, individual elements.
Bollard Lighting, Ferry Landing, Galveston
Figure 4-20: Bollard Lighting, Ferry Landing, Galveston

4.3.4 Lighting & Plant Materials

The placement of plant materials must be done with knowledge of the photometrics and pole placement for the highway. In general, high mast lighting will not be affected by plant material placement due to the height of the light source. Plant material, however, should not be placed immediately next to the mast, since lowering the lighting for maintenance requires a clear zone.
Where standard pole mounted fixtures are used, placement of plant materials becomes more critical. Trees must be placed so future growth will not interfere with the light source. As a rule, trees should not be placed forward of any light standard.
Lighting may also be used to highlight trees in a landscape design within the ROW.

4.3.5 Dark Skies Fixture Types

Selected luminaires should have the
International Dark Sky Association
(IDA) Seal. This third- party seal certifies that outdoor fixtures minimize glare, while reducing light trespass and sky glow. To minimize light pollution, dark skies fixtures should:
  • Only light the area needed;
  • Be no brighter than needed;
  • Minimize blue light emissions; and
  • Be fully shielded, so that the light bulb is not visible.