LED illumination has progressed substantially as a sign lighting media, and is now generally regarded as the primary illumination product for channel letter signage. However, LEDs must be configured and installed properly to generate optimal channel letter illumination. This article details some of the “best practices” associated with the use and placement of LED modules in channel letter signage.
What is accomplished when these best practices are used? They are:
- Illumination Brightness – the letter luminosity is clean and vivid
- Illumination Evenness – light dispersion is equal across the entire letter face or halo
- Lighting Consistency – each sign element (letters and/or logo box) has equivalent brightness
- Color Optimization – the LED configuration utilized is appropriate for the face color
- No Module Visibility – LED mounting locations are not visible when viewing the illuminated sign
Proper execution of these practices produces a compelling and vibrant letter sign that will generate referrals for your signage business.
Module Placement Planning
First, the initial best practice is to review the LED module manufacturer specifications prior to planning the module placement. Many LED producers provide a “single stroke” recommendation for their modules (in this context, a “stroke” is the side to side width of the letter return.)
For example, if your channel letter has an 8” stroke width (which is large) and the manufacturer recommends a maximum 6” stroke for a single strip of LED modules, then two strips of LED would be necessary for bright letter illumination.
LED Module Placement Diagram
However, a competent letter vendor will never accept the manufacturer’s guideline without testing and observation. Each LED brand has illumination nuances which can only be observed through actual use.
One excellent practice is to produce and illuminate a test letter when populating a new brand of LED. The completed initial letter is then evaluated for luminance, evenness and lighting consistency prior to populating the remainder of the sign.
Finally, a quality LED layout plan will also include a review of the letter structure and design prior to deciding on the quantity and position of the modules. If the letters include serifs or other decorative elements, the LED placement must be adjusted to account for any potential lighting issues resulting from the channel width variance.
How to Generate Even Face Illumination
Another illumination objective is even illumination across the entire letter face (i.e., the entire face acrylic or halo area is equally bright.) For front-lit letters, two lighting conditions to avoid are “tiger striping” and hot spots.
Both of these issues refer to one area of the face being significantly brighter than an adjacent area. A “tiger stripe” refers to an entire strip of the letter face that is visibly brighter than a bordering strip.
Tiger striping is typically observed when the LED modules have a viewing angle that is too narrow. If too much of the “sweet spot” (brightest part) of the illumination is focused on a narrow vertical strip, then it may take on a brighter appearance than an adjacent strip of the face. Using an LED with a wider viewing angle will typically solve this issue.
By comparison, a “hot spot” can mean one of two different conditions. It may refer to a smaller face area that is significantly brighter than an adjacent area, or it may mean that the LED modules are actually visible through the face acrylic.
Smaller hot spots (one area brighter than the next) can have several causes. One potential cause is the sign did not receive a power supply that is capable of delivering enough power to properly illuminate the entire module population. Modules that are further down the LED series may not be receiving sufficient current. This scenario is more likely with constant voltage LED (instead of constant current.) A power supply with sufficient current may address this problem.
The visible module hot spot condition is typically observed with specific shades of blue, green and yellow letter face acrylic. Certain shades within that color set have a high degree of translucency, and an illuminated LED module may actually show through the face.
Low acrylic density is another potential cause of LED module visibility. Face acrylic is available in both 1/8” and 3/16” thickness. Lower density face acrylic (1/8” thickness) is obviously more susceptible to LED module visibility.
One approach to addressing visible modules is placing diffuser film on the letter face interior. This material helps to control the light distribution within the letter and produce an even illumination appearance.
Colored LED Illumination
Another LED product can increase the intensity and effectiveness of a channel letter set – colored illumination. Some LED producers offer modules which emit colored lighting instead of standard white, and professional usage of that product can also be an illumination best practice. However, colored LED modules often have a higher cost than standard white.
For example, channel letters with red face acrylic will sometimes be populated with red LED instead of standard white. This configuration can be necessary because certain shades of red acrylic take on a pinkish color when illuminated with white LED. In this simple channel letter configuration (red acrylic face without vinyl or diffuser film), red LED may preserve and increase the “redness” of the intended face color and can be a best practice.
However, that scenario assumes the entire sign has the same red acrylic face layout. The situation changes if one part of the sign has standard acrylic while another part has a vinyl face pattern (such as a logo box mounted adjacent to a letter set.)
In that example, using red LED throughout the entire sign is probably not a good idea—it will benefit the letter faces but could cause a problem within the logo box. White LED may produce a superior logo box appearance. So, for optimum illumination this sign would include both white and red LED modules.
Also, the practice of matching the LED color to the face color does not necessarily carry over to other configurations. For example, some LED producers offer modules with orange illumination. However, orange acrylic does not typically require orange LED for effective lighting. White LED usually works fine for orange face acrylic illumination. In this case, the higher cost of colored LED is typically not warranted.
Blue LED is one more example. This color can also present challenges when improperly used. Dark blue acrylic already has an inherent issue of absorbing much of the letter illumination rather than emitting it, and can result in a dark letter appearance. Combining blue LED with dark blue acrylic may compound this problem.
However, blue LEDs can present a striking appearance for halo lighting of reverse-lit channel letters. So a blue LED certainly has legitimate applications but it must be used with caution for front-lit channel letters.
Interior Can Treatments
The composition of the letter return itself also contributes to the LED illumination performance. Reflective paint for the return interior (inside of can) is available for the purpose of both increasing and improving letter illumination.
Traditional channel letters have a standard 5” return depth. That means the illumination must travel a full five inches from the module prior to reaching the letter face. That seemingly small distance may actually have serious implications.
First, the LED light actually “bounces” from side to side of the letter interior prior to reaching the face. If the letter can interior is untreated, that bounce can mean the light luminosity received by the acrylic actually decreases prior to reaching the face. This bouncing is also called “ricochet lighting.”
Ricochet lighting occurs because of the LED module viewing angle, or “fan of light” produced by each module. Some of that light fan will bounce—possibly repeatedly—off the return wall prior to reaching the face. That internal ricochet can produce a compromised level of face lighting consistency and brightness if the interior of the return is untreated (standard aluminum.)
A painted letter interior will help to increase the lighting ricochet and take full advantage of the LED capabilities. This configuration will typically have a superior illuminated appearance compared to a set with an unpainted interior and can be a best practice when used properly.
White is the interior color of choice because of the high light reflectance value (LRV). Typically white has an LRV of over 80 percent, and this means a bright reflection of the interior light and subsequent brighter face illumination.
In addition, demand for 3” channel letter returns (rather than 5” depth) has been increasing. This shallower distance reduces the internal light bounce and focuses more of the “prime” LED illumination onto the acrylic face.
LED modules have evolved into the primary source of illumination for channel letter signage. However, they must be used properly for clean, even and bright letter signage illumination. Following these practices increases the chances that your client will receive a professional and well-illuminated channel letter set.