Anchor: #i1002293

Section 3: Luminaires

Anchor: #i1004431

Introduction

The luminaire (pronounced loom-in-air) is the complete lighting unit (or fixture), including the light source, reflector(s), lens, and housing. This section describes some of the common types of luminaires and their uses.

Anchor: #i1002304

Conventional Luminaires

Conventional roadway luminaires consist of cast aluminum housings with flat or sag glass lenses and polished aluminum reflectors. They are commonly called “cobra heads.”

These conventional units are usually mounted no higher than 50 feet. Typical sizes and mounting heights are:

  • 250 watt HPS at 40 foot MH (mounting height)
  • 400 watt HPS at 50 foot MH
  • 150 watt HPS where lower mounting heights are necessary (such as near airports).
Anchor: #i1002334

Mounting of Luminaires

“House side mounting” refers to the placement of luminaires between the curb and right-of-way line.

“Median mounting” refers to placement on open medians or medians with concrete traffic barrier.

See Chapter 6, Section 7, for complete discussions of House Side Lighting and Median Lighting.

Anchor: #i1002357

Cutoff

For roadway luminaires, the point on the ground directly below the light source is called the “nadir.”

Reduction of the luminous intensity (candlepower) in the upper portion of the light beam above nadir is required to control glare or reduce the amount of light falling off the right-of-way. Luminaires that feature this type of control are called “full-cutoff,” “cutoff,” and “semicutoff.”

The candlepower of luminaires designated as full-cutoff, cutoff, and semicutoff is limited at angles at 90 and 80 degrees from the nadir (see Figure 5-2).

The following table shows the requirements for full-cutoff, cutoff, semicutoff, and noncutoff type luminaires.

 The candlepower of luminaires designated as full-cutoff,
cutoff, and semicutoff is limited at angles of 90 and 80 degrees
from the nadir. (click in image to see full-size image)

Figure 5-2. The candlepower of luminaires designated as full-cutoff, cutoff, and semicutoff is limited at angles of 90 and 80 degrees from the nadir.

Anchor: #i1001231Candlepower Cutoff Requirements for Different Luminaire Types

Luminaire Type

Percent of Total Candlepower at 90° from Nadir (Horizontal)

Percent of Total Candlepower at 80° from Nadir

Full-cutoff

0%

10%

Cutoff

2.5%

10%

Semicutoff

5%

20%

Noncutoff

No limitation in either zone.

NOTE: In some cases the cutoff distribution may meet the requirements of the semicutoff, and the semicutoff may meet the requirements of the noncutoff.



Texas Health and Safety Code, Chapter 425, “Regulation of Certain Outdoor Lighting,” requires the use of cutoff luminaires (2.5% at 90° and 10% at 80°) for roadway lighting. The full text of the law is available on the Internet at http://tlo2.tlc.state.tx.us/statutes/hs.toc.htm

Anchor: #i1002398

Light Distribution Patterns

The Illumination Engineering Society (IES) writes many of the industry standard specifications for fixtures. The IES has designated several standard types based on their light distribution patterns. Figure 5-3 shows plan views of light distribution patterns for the basic types of conventional luminaires.

 Plan views of light distribution patterns
for basic types of conventional luminaires. (click in image to see full-size image) Anchor: #i999649grtop

Figure 5-3. Plan views of light distribution patterns for basic types of conventional luminaires.

Typical roadway illumination fixtures that TxDOT uses are IES type MC-II and MC-III (medium-cutoff, type II and III distribution patterns).

Anchor: #i1002422

Underpass Luminaires

Underpasses may require a special 150 watt HPS cobra head or induction fluorescent luminaires mounted on caps or special brackets.

Where structures are higher than 25 feet above the roadway, the 250 watt luminaire may be used.

Anchor: #MLEGLNKE

High Mast Lighting

High mast lighting units are mounted at heights of 100 feet or more and use high pressure sodium light sources. The following table shows the three types of high mast lighting, their photometric characteristics, and their typical light sources.

Anchor: #i1001259Types of High Mast Lighting

Type

Photometric Characteristics

Symmetric Luminaires

Fixed position, cuttoff luminaires provide a circular lighting pattern. Similar to IES Type V.

Asymmetric Luminaires

Similar to symmetric, except lighting pattern can be adjusted to provide elliptical or oblong pattern.

Note: There are three types of asymmetric high mast luminaires:

  • Type A — similar to IES Type II
  • Type B — similar to IES Type III
  • Type C — similar to IES Type IV.


Light Source. The typical light source for high mast lighting units consists of twelve 400 watt HPS lamps.

Previous page  Next page   Title page