LEDs and LED Reflector Design Challenges, Part 2

LED light output is highly directional. That means LEDs require sophisticated reflectors, placement angles, and lenses to satisfactorily disperse the light. While the LEDs are supplied by various manufactures, the housings, reflectors, light diffusers, collimators, and lenses are carefully designed, engineered, and assembled by the lightbar manufacturers. In many cases, these components are proprietary to that particular manufacturer.

This poses some special problems considering the somewhat limited viewing angles at the ends of linear lightbars, and the fact that even clear end-caps tend to distort light-rays. Some manufacturers installed more powerful LED modules at 45-degree angles to improve visibility when the vehicle enters intersections. Others have gone to “U” or “V”-shaped lightbars to ensure 360 degrees of coverage.

The reflector design is a critical component of LED lighting. Reflectors are shiny, chrome-plated plastic or sometimes polished aluminum or stainless steel. Some manufacturers utilize multiple rows of LEDs offset at slightly different angles to obtain a broader range of visibility.

One light-dispersing method is a collimator, a light-modification device that has been around for centuries. The collimator is a clear plastic or glass tube mounted between the LED and outer lens, which can absorb light and then redirect it, ultimately spreading the beam into a wider pattern. Its function is similar to that of a neon light, which bends the light into the form of the tube.

Another optical device that successfully adapted the LED to be viable for emergency lighting is the Fresnel lens. Far from being a new invention, the Fresnel lens has been used in lighthouses and other optical devices since 1823. Essentially, the Fresnel lens consists of a series of prisms meticulously ground into a clear surface—glass or plastic—which modifies the light beams, allowing them to be visible over farther distances.

The directional lighting characteristics of LEDs mean that spreading the light out is the major design challenge. Of the dozen or so lightbar manufacturers, here is a sampling of how some of them are solving the LED reflector or lens challenge with their latest LED modules and an example of lightbar with that module. Heads-up! Each manufacturer still makes older generation lightbars with previous LED module designs.

 

Code 3® PSE

www.code3pse.com

Code 3 uses the most different ways of spreading out the LED light. The TriCore® TC2 module is used in their Defender lightbar. The PriZm™ II module is used in their RX 2700™ CC MultiColor (MC) lightbar. Other Code 3 lights and lightbars use SIRIS™ (structured internal reflector illumination system) LED modules, Torus™ LED modules XT-series LED modules and LED X™ LED modules.

The TriCore is the latest Code 3 technology, and is one of the brightest LED lightheads on the market. TriCore is unique and significant because it does not use mirrored reflectors. Instead TriCore uses long, thick and optically clear lenses (collimator) to funnel and selectively diffuse the light. The light passes through a convex lens surface, which mates up to a larger diameter, opposing convex lens. The entire module is mounted in a clear housing, which may or may not have areas of grooved or roughened surface to further reflect the light.

 

The PriZm II is a polished reflector LED module. The large outer reflector has a parabolic shape, but the inner part of the reflector has at least four other reflecting surfaces. The long and narrow inner reflector stands off a bit from the LED emitters, is mirrored on both sides, and reflects light from the outer parabolic surface. However, some of the LED output from each emitter goes straight into the inner reflector where it is reflected by angle boxed mirrored surfaces on all four sides.

The Torus is a NextGen replacement for the Optix lightheads. These use Total Internal Reflection technology. This is essentially a long lens mounted in front of the LED emitters, which are mounted directly to the circuit board. That lens has the exact cross-section of the Fresnel lens. A Fresnel lens was first used in lighthouses to magnify the light output from a mere lantern as a distant warning signal. This is a very small, thin LED module but makes maximum use of the light.

The TriCore LED (dual-color) LED module is used in Code 3 lightbars like the Defender TC2 (MultiColor). The MultiColor (dual-color) PriZm II LED module is used in Code 3 lightbars like the RX 2700CC MC. Torus MultiColor (dual-color) LED module is used in Code 3 lightbars like the 21TR Plus MuliColor. The dual-level Triumph™ lightbar uses SIRIS LED modules.

 

D&R Electronics

www.dandrelectronics.com

D&R Electronics recently introduced the WDR12, their newest LED module. It sets the standard for the most reflected LED light from the simplest reflector. All LED modules from every lightbar manufacturer involve the LED emitter soldered directly to a printed circuit board. All these printed circuit boards have some kind of aluminum heat-sink attached to the board.

The WDR12 module is simply a chrome-plated reflector mounted directly on top of that circuit board. No multiple reflectors, no lenses, just the reflector, proving that a great reflector design will definitely do the job.

The WDR12 one-piece reflector is quite a clever, complex design based around a very deep parabolic shape. It fits tightly around each LED emitter and opens up more like a long megaphone than a pure parabolic shape. The reflecting surfaces above and below the LED emitter are molded in a scalloped profile, each forming a separate reflection, then each reflecting off the overall reflector. As the light exits the reflector, it passes through a diffused clear cover.

The Prowler is the new generation linear lightbar from D&R. The Prowler uses the WDR12 LED module and meets applicable SAE Class 1 and California Title 13 requirements. The Prowler has selectable flash patterns, has an optional auto dim mode, and is available with six or 12 LED modules.

 

 

Federal Signal

www.fedsig.com

FedSig uses the Solaris® LED module in their Valor® lightbar. The LED light is emitted up from the printed circuit board onto a mirror-finish plastic reflector. Manufactured with ROC (Reliable Onboard Circuitry™), the Valor has fewer failure points than a typical lightbar.

The chrome-appearing, ripple-textured reflector has a parabolic shape for the forward light signal. The inner sides of the LED module are also reflective. Some reflectors use sides with a 90-degree angle for the most forward signal. In other locations on the lightbar, the sides are at a 45-degree angle for the best off-axis signal.

The Solaris reflector is simple and very straightforward. It is the perfect reflector design for the non-linear shape of the Valor. The Solaris produces a very strong forward signal, so the Solaris module is simply mounted in the direction the light is needed, i.e., pointing forward or pointing off-axis.

Valor is built with FedSig’s Solaris LED reflector technology. The non-linear shape of the Valor™ lightbar provides 360 degrees of light output and off-axis lighting at critical intersection points. In combination with its specific shape, the Valor also uses SpectraLux™ multicolor LED technology. SpectraLux technology provides the ability to change LED colors for combinations of Amber, Blue, Red or White. Other lightbars that use the Solaris LED reflector technology include the Integrity, Legend and Vision SLR.

 

SoundOff Signal

www.soundoffsignal.com

SoundOff Signal uses the Nexus LED module in their nFORCE® lightbar. The use of Nexus Technology in the reflector is a reinventing of the LED light module for SoundOff. The LED emitter was upgraded and so was the exact shape and form of the plastic reflector. Nexus Technology, or nFORCE, is what defined the final shape of each reflector. The goal for any lightbar manufacturer is the optimum balance between the forward light output (reflection) and the off-axis or intersection light output.

The LED modules in SoundOff Signal’s lightbars have previously used Total Internal Reflection (TIR) technology. The LED light output was collected internally and dispersed via collimator lenses, i.e., the light output did not involve reflected surfaces. With Nexus LED modules, the texture, profile, internal reflecting surfaces, and curvature of the mirror design do all the reflecting. This gives SoundOff Signal the capability of precisely controlling and tailoring the amount of forward and off-axis light.

SoundOff Signal uses many different designs of reflector in their new nFORCE line. The center of the Nexus Technology nFORCE modules has a wavy texture on an elliptical profile to diffuse the light forward. The sides of the nFORCE module are specifically designed to reflect light off-axis. That said, SoundOff Signal diffuses the off-axis light two different ways—one for external lightbar, one for internal lightbar. Of course, the take-downs and alley lights use a long-range focused beam.

The Nexus Technology LED modules are used in the nFORCE exterior and interior lightbars, directional warning, and surface-mounted perimeter lighting. These are all available in Bronze (single color), Silver (dual color) and Gold (tri-color).

 

Star Signal Vehicle Products

www.star1889.com

The newest lightbars from Star Signal Vehicle Products use a combination of, or the options of, three different LED modules. One is the brand-new Lineum™ LED lighthead, which uses six Gen IV LEDs. The Star Lineum LED technology produces a wide-angle light distribution and is used primarily on the front and rear heads. Importantly, the Lineum module is also capable of dual color to the front for takedown/pursuit and to the rear for traffic director.

The Star SVP High Density™ LED lighthead also uses Gen IV LEDs with 12 or 18 LED head versions available. This is the module designed to meet high LED count bid specs. The wide-angle light distribution achieves SAE Class I rating without the use of flashing alley lights.

The Star SVP Starburst™ LED lighthead uses eight Gen IV LED in a narrow light distribution. A general-purpose LED module, Starburst is compatible with end or front facing heads, traffic directors and stop/tail/turns, and can be programmed for takedown/pursuit.

The LASER® is Start SVP’s newest generation of low-profile lightbars. It uses Laser Cage Technology™ componentry design, i.e., the ability for each modular head to be interchangeable with other modular heads for multiple custom configurations. The Versa Max™ Razor lightbar also uses the dual-color Lineum LED module.

 

Tomar Electronics

www.tomar.com

The Tomar LED module uses a short but very complex collimator design, i.e., a clear lens mounted on top of the circuit board-mounted LED emitter. The plastic enclosure has a very aggressive, fine-ribbed texture to further diffuse the LED light output. The magnifying effect of the collimator is quite dramatic.

The typical single-color LED module for the front or rear location may have six LEDs in a staggered row while the dual-color LED modules will have 12 LEDs. The typical single-color LED module for the corner locations may have 12 LEDs, while the dual-color versions have 24 LEDs.

The 970L Scorpion™ lightbar is the latest from Tomar. It continues in the same basic design of extruded aluminum housing and cast-aluminum end caps; however, the Scorpion is a very low-profile lightbar. It is available in 10 different lengths from 21 inches to 80 inches.

 

Whelen® Engineering

www.whelen.com

Whelen Engineering uses the Linear LED® Super-LED® (linear technology) LED module in their Liberty™ II lightbar. LED light is not just reflected or diffused using mirror-surface plastic and aluminum. LED light is also diffused, spread out, and in some cases amplified by passing through a clear plastic optic or lens.

The Collimator™ patented design captures, collects and focuses LED light with an extremely simple design involving a Fresnel-like lens running the entire width of the reflector and a large, parabolic-shaped, highly polished reflector.

The Whelen Liberty II SOLO™ lightbar uses single-color inboard and corner LED modules. The Whelen Liberty II DUO+™ lightbar uses dual-color LED modules for the inboard and corners. The DUO modules have the LED emitters placed on the circuit board with interleaved colors, for example, red and blue alternating, red and amber alternating, or blue and white alternating.

The NextGen Liberty II lightbar has 30 percent more illuminated surface area than the original Liberty lightbar. A photocell that automatically dims the light at night while still meeting SAE Class 1 is optional on the Liberty II SOLO and standard on the Liberty II DUO.

 

The Same But Different

Nearly every modern lightbar uses virtually identical LED emitters. There is some variation of color as some of these LEDs heat up, so evaluate the LED lightbar after it has been activated for 30 minutes or so. However, LED emitters used by nearly all lightbar manufacturers today are all basically the same design and the same quality.

The difference between lightbars today is not the LED emitter, but how each manufacturer collects, magnifies, focuses, deflects and then diffuses that light output. Some companies use very complex reflectors or collimators, while other companies use very simple lenses, reflectors and diffusers.

All companies achieve a balance of forward and off-axis (intersection) warning signal. Some do it with a combination of narrow-focus and wide-focus lenses and reflectors. Some do it by simply pointing a narrow-focus LED module forward for a forward signal and at an angle for an off-axis signal. Every single one of these LED modules and lightbars is different, i.e., they all achieve the same goals by different means. Check them all out.



Published in Law and Order, Feb 2015

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