Light Emitting Diode (LED) Signs

General Specifications and Requirements

1.0 Scope & Background

1.1 This document provides an overview of the technical requirements needed to manufacture safe and reliable signage for use in traffic control.

1.2 Advances in technology have made possible, and practical, traffic signage that utilizes solid-state light sources in place of traditional incandescent lamps. Solid-state light source signs, when designed and manufactured correctly, are far more reliable than incandescent based signs and require little or no maintenance. Solid-state signs generally use only a small fraction of the power of incandescent lamp based signs and so, therefore, are more economical to operate.

Solid-state light sources are more commonly known as LEDs or Light Emitting Diodes. LEDs are closely related to transistors while incandescent lamps are closely related to vacuum tubes.

LEDs are “Solid-state” devices because they are made of semi-conductor material held in a solid form that does not move and are virtually insensitive to movement or vibration of the component. The part can be thought of as monolithic from a user’s prospective. This property helps make LEDs mechanically very durable.

No heat is needed for LED light generation. LEDs work at the atomic level converting “electron energy state changes” directly into photons. This process is efficient and produces very little waste.

LEDs can last in excess of 10 years of continuous lighted use when operated under proper electrical and environmental conditions. Under intermittent use, LEDs could last more than 20 years in the field. LEDs do lose inconsequential brightness slowly over many years’ time.

2.0 General

2.1 The LED sign shall be capable of displaying the message when energized and be effectively blank when not energized. Most messages listed in Manual of Uniform Traffic Control Devices are available. Custom messages to fit various situations are also available upon request. Specific legend, character size and color will be clarified on a per sign basis.

3.0 Mechanical

3.1 The sign shall be constructed using a weatherproof, aluminum housing with outside dimensions being 2 7/8” larger than the designated face size. The housing shall consist of an 8” deep, .125” thick, extruded aluminum body, and a .063” aluminum back. All corners are TIG (Tungsten Inert Gas) welded to provide a weatherproof seal around the entire housing.

3.2 The door shall be constructed of .125” thick extruded aluminum. Two corners are TIG welded with the other two screwed together to make one side of the door removable for installation of the faceplate and polycarbonate lens. The door is fastened to the housing on the left by a full length, .040” x 1 ¼” open stainless steel hinge. The door shall be held secure onto a 3/4” wide by 5/32” thick neoprene gasket by one quarter-turn link lock.

3.3 A three-sided visor made of .063” aluminum shall be fitted to the door to act as a sunshade and improve the visibility of the message.

3.4 All surfaces of the sign shall be etched and primed in accordance to industry standards before receiving two color coats of industrial enamel.

3.5 All fasteners and hardware shall be corrosion resistant stainless steel. No tools are required for routine maintenance.

4.0 Electrical – Wiring/Control

4.1 A 1-amp rated fuse shall be mounted in the primary Hot AC power line for each power supply. If a relay is needed for controlling On/Off for multi-message signs, it may be mounted internally, or externally to allow easy-access servicing.

4.2 Field wires shall carry the control voltage of 120VAC to the sign and connect to a barrier type terminal block. All terminals shall be clearly marked as to their function.

4.3 LEDs will be wired in series strings of appropriate length using #26AWG Kynar insulated wire wrap type wire. A minimum of four turns shall be made for each connection.

5.0 Electrical - Power Supply

5.1 The power supply for the LEDs shall convert 120VAC into 48VDC. The power supply shall have a rated load current of 1.1 amperes each with a voltage regulation of 2% or better from 10 to 100% load, with a terminal block connection for input and output. Noise and ripple on the output shall not exceed 500mV Peak to Peak or 200mV RMS. The power supply shall have the ability to operate at 55C at full load. Two identical power supplies will be incorporated into each sign. Each supply is capable of handling the full load independently. This provides redundancy and thereby increases reliability of the system.

5.2 Power to LEDs will be delivered through a custom Printed Circuit Board (PCB). PCB shall be capable of allowing two power supplies to be properly paralleled using diode isolation between positive terminals of the supplies.

5.3 PCB substrate material shall be 0.062” thick G-10 glass laminate of FR-4 grade and comply with UL-94VO flame-retardant specification. The PCB shall limit LED current to18ma for maximum reliability. A method of precision current adjustment must be incorporated in the PCB to facilitate matching current between different colored strings of series wired LEDs. Connection of the LED series wired strings shall be made by a minimum of five wire wrap turns around a 0.025” square wire wrap pin for maximum reliability.

6.0 LEDs

6.1 All LEDs will be mounted so as to protrude through the faceplate between 0.123 and 0.133 Inches. Mounting Clips shall secure the LEDs to the faceplate. The clip shall be a one-piece configuration of a black plastic. The clip will have the LED inserted into and will securely align and hold the LED in position perpendicular to the faceplate. LEDs shall have a minimum viewing angle of 60 degrees both horizontal and vertically ( +/- 30 degrees from center line axis) and a maximum viewing angle of 90 degrees (+/- 45 degrees from centerline axis). Apparent spacing between LEDs shall be uniform. Spacing may vary slightly when measured numerically to compensate for crossing over of two or more messages and for optimal appearance of all letters, symbols and numbers. Sign must look as symmetrical and attractive as possible.

7.0 Environmental

7.1 Operating and storage temperature range shall be –40 to +50 Celsius. Operating and storage humidity range shall be 10 to 90 % non-condensing. Operating altitude is 10,000 feet maximum. Storage altitude is 40,000 feet maximum.

8.0 Electromagnetic Compatibility

8.1 System shall meet FCC part 15-A for radio interference and conducted line noise.

9.0 Reliability

9.1 The LED sign unit utilizes LEDs with 100,000 hour rated life. This assumes no physical damage from external sources such as mechanical impact, fire, lightning strike, etc.

For more information, contact

Jim Livingston livingston52@sbcglobal.net

or Christy Merkel cmerkel@trafficsignsinc.com.

Thank you for your interest!

Last Updated: October 2006