Appendix A – Light Emitting Diode (LED) Signal Modules

Standards for LED Signal Modules in Warning Systems

1. Definitions

Candela (cd) – SI unit of luminous intensity. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 nm and that has a radiant intensity in that direction of 1/683 W per steradian (1 cd = 1 lm/sr).

Lumen (lm) – SI unit of luminous flux. Luminous flux emitted in unit solid angle [steradian (sr)] by a uniform point source having a luminous intensity of 1 candela (1 lm = 1 cd x 1 sr).

Luminance Lv (in a given direction, at a given point on a real or imaginary surface) – quantity defined by the formula:

  Lv  =    dΦv / dA • dΩ • cosθ

where dΦv is the luminous flux transmitted by an elementary beam passing through the given point and propagating in the solid angle dΩ containing the given direction; dA is the area of a section of that beam containing the given point; θ is the angle between the normal to that section and the direction of the beam (footlambert, cd/m2).

Luminous Efficacy of Radiation (K) – the luminous flux Φv divided by the corresponding radiant flux Φe

(K = Φv/Φe).

Luminous Intensity (Iv) (of a source in a given direction) – the luminous flux dΦv leaving the source and propagating in the element of solid angle dΩ containing the given direction, divided by the element of solid angle (Iv = dΦv / dΩ candela).

Luminous Flux (Φv) – quantity derived from radiant flux Φe by evaluating the radiation according to its action upon the CIE standard photometric observer (lumen).

Rated Voltage – the nominal or design operating voltage of the LED signal module; the voltage at which rated watts, candelas, and life are determined.

Rated Watts – the average initial power (watts) consumed when the lamp is operated at rated voltage.

2. Photometric Requirements

2.1 Luminous Intensity

When LED signal modules are in use at a warning system, they must meet the minimum luminous intensity values shown in Table A-1.

Table A-1 – Minimum Luminous Intensity (Candela) over Temperature and Lifetime

Table A-1 outlines de minimum luminous intensity over temperature and lifetime of light emitting diode (LED) signal modules
  5°Left (L)/Right (R) 10°L/R 15°L/R 20°L/R 25°L/R 30°L/R
400 375 250 150 75 40 15
5°Down (D) 350 325 250 150 75 40 15
10°D 130 125 110 85 60 35 15
15°D 45 40 35 30 25 20 15
20°D 15 15 15 15 15 15 10

2.2 Chromaticity

A signal module must produce a uniform red light output as specified in article 4.2 of the Vehicle Traffic Control Signal Heads – Light Emitting Diode Circular Supplement, published by the Institute of Transportation Engineers, dated June 2005.

2.3 Uniformity

The ratio of the greatest and least luminance on the signal module must not be more than 5:1, when measured over average areas of 500 mm2.

2.4 Rise/Fall Time

The maximum rise time from zero intensity to full intensity, and the maximum fall time from full intensity to zero intensity, must be 75 ms.

3. Physical and Mechanical Requirements

3.1 LED Signal Module Design

3.1.1  The LED signal module must be designed to fit the grade crossing light unit housings, described in Part 3.2.35 of the AREMA Communications and Signals Manual (cited in Part A), without requiring modification of the mechanical, structural, or electrical components.

3.1.2  The LED signal module must be either 200 mm or 300 mm in size.

3.1.3  The LED signal module must have either a clear or a red lens.

3.1.4  Any gasket or similar sealing provisions must be made of a material as specified in Part 15.2.10 of the AREMA Communications and Signals Manual (cited in Part A).

3.2 Environmental Requirements

3.2.1  The LED signal module must operate over an ambient temperature range of -40°C (-40°F) to 70°C (158°F) in accordance with sections 1 to 3 of the "Method 1010.8 Temperature Cycling", dated June 18, 2004 of MIL-STD-883H, Test Method Standard, Microcircuits, published by the United States Department of Defence, dated February 26, 2010 and must satisfy the failure criteria set-out in article 3.3 of that standard, and any reference to end-point measurements and examinations are to be read as those provided by the supplier.

3.2.2 The LED signal module must be protected against dust and moisture intrusion in a Type 4 enclosure in a manner that meets the requirement of article 8.6.2 of the Canadian Standards Association standard CAN/CSA-C22.2 No. 94.2-07 entitled Enclosures for Electrical Equipment, Environmental Considerations, as amended from time to time, when tested in accordance with article 8.6.1 of that Standard.

3.2.3 The LED signal module must meet mechanical vibration and shock requirements as specified in Part 11.5.1 of the AREMA Communications and Signals Manual (cited in Part A).

3.2.4  The LED signal module lens must be UV stabilized.

3.3 Identification

3.3.1  The LED signal module must have a label containing the following information:

  1. the LED colour;
  2. the beam deflection classification;
  3. the operating voltage;
  4. the current consumption at operating voltage;
  5. the module’s serial number; and
  6. the date of manufacture.

3.3.2  If the module or its components require orientation, they must be prominently and permanently marked with an indexing arrow.

4 Electrical Requirements

4.1 Transient Voltage Protection

LED signal module circuitry must include voltage surge protection as specified in Part 11.3.3 of AREMA Communications and Signals Manual (cited in Part A).

4.2 LED Drive Circuitry

LED signal module circuitry must operate as specified in Part 3.2.35 of the AREMA Communications and Signals Manual (cited in Part A).

4.3 Dielectric and Electromagnetic Interference

LED signal module circuitry must conform to dielectric and electromagnetic interference requirements for Class B equipment in Part 11.5.1 of AREMA Communications and Signals Manual (cited in Part A).

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