Principles of Lightbox Calculation. Or How to Properly Place LED Modules in Advertising

Uniform illumination of the surface, installation features.
 

     The first question that the client faces is at what distance from the surface the LED strip should be placed to achieve uniform illumination of the surface.
     Let's try to understand the essence of the issue. As is known from the characteristics of the strip, the most common parameter is "illumination angle - 120 degrees". What does this mean? LED manufacturers claim that this is the angle at which the light from the LED element falls. So, let's look at the diagram provided by the manufacturers in the Data Sheet SMD 5060:
As we can see from the figure, the light is not distributed completely uniformly, and at a certain distance and at certain angles there are zones of greatest illumination. Thus, the LED obviously provides maximum illumination strictly perpendicular to the center. Let's try to determine experimentally using the example of a strip based on SMD3528 LEDs how the light is distributed and at what distance from the elements we can get uniform illumination. Let's take an LED cable and place it on the surface in direct contact with a sheet of paper on which a 10-millimeter grid is applied. Let's turn on the backlight. Look at the picture:
 

	As we can see from the picture, in close proximity to the surface, we have uneven illumination, at a distance of 15 mm from the mounting edge.
	Let's try to cover the tape with an opaque plate at a distance of 10 mm from the mounting edge and look at the result. As we can see, the unevenness has become unnoticeable. Thus, we come to the conclusion that when directly mounting the strip on the illuminated surface, the strip should be recessed to a depth of 10-15 mm.
	the depth can be reduced by raising the strip above the illuminated surface by the same 10-15 mm. In these two photos, we see what kind of lighting effect we get by increasing the distance from the illuminated plane to the strip by 20 mm. We got an even and soft light. Thus, it is obvious that the optimal location of the LED strip is approximately 10 mm from the surface and recessed into the depth at a distance of also approximately 20 mm. It should be recessed in order to hide the strip itself from the observer. The depth of recessing should be selected depending on the viewing angle of a specific installation location. Simply put, do it so that the strip is not visible.
There is often a need for edge lighting, when the strip is parallel to the illuminated surface and the light falls on it perpendicularly. Let's see what the backlight looks like when it is parallel to the surface. In this example, we also see that 10 mm is enough to provide uniform contour lighting.

Having modeled the characteristics declared by the manufacturer on the scale of an LED strip, we obtain the following diagram:


We see that the maximum peak illumination spots are obtained at a distance of 13 mm. from the LED, the overlap of the illumination zones occurs at a distance of 6 mm from the edge of the diode. Thus, uniform illumination occurs at a distance of 15 mm. Which we have confirmed experimentally.

The distance from the strip to the illuminated surface and the distance between the strips when calculating lightboxes are calculated in a similar way.
So we will summarize the main calculation data in a table: