# How is a segment illuminated in a typical 7-segment display?

#### kgstewar

Joined Apr 5, 2012
152
Consider a common 7-segment display, like this one. I noticed in the datasheet schematic, they show one LED per segment, which may just be schematic, although for a larger display they show 3 LEDs per segment, so maybe they are showing the actual number of LEDs per segment. In any case, here is my question:

How is a display segment in a 7-segment display constructed such that one LED can uniformly illuminate the entire segment?

I have tried to make my own LED segment by putting an LED behind some partially translucent white acrylic. I always get a fairly localized bright spot and not the uniform illumination that you get in a 7-segment display. Maybe I just need to line up more LEDs for each segment? Or is there a trick?

thanks,

Kevin

#### hp1729

Joined Nov 23, 2015
2,304
Consider a common 7-segment display, like this one. I noticed in the datasheet schematic, they show one LED per segment, which may just be schematic, although for a larger display they show 3 LEDs per segment, so maybe they are showing the actual number of LEDs per segment. In any case, here is my question:

How is a display segment in a 7-segment display constructed such that one LED can uniformly illuminate the entire segment?

I have tried to make my own LED segment by putting an LED behind some partially translucent white acrylic. I always get a fairly localized bright spot and not the uniform illumination that you get in a 7-segment display. Maybe I just need to line up more LEDs for each segment? Or is there a trick?

thanks,

Kevin
I think all possibilities are apparent. Consult the data sheet for the display you are considering.

#### dl324

Joined Mar 30, 2015
12,223
How is a display segment in a 7-segment display constructed such that one LED can uniformly illuminate the entire segment?
The cavity the LED is in is filled with a material that diffuses the light emitted by the LED. The surfaces of the cavity are also reflective.
I have tried to make my own LED segment by putting an LED behind some partially translucent white acrylic. I always get a fairly localized bright spot and not the uniform illumination that you get in a 7-segment display.
Your results will never be as good as a display that considers angles of reflection and the interface between the LED package and your difusing medium.

#### kgstewar

Joined Apr 5, 2012
152
The cavity the LED is in is filled with a material that diffuses the light emitted by the LED. The surfaces of the cavity are also reflective.
Your results will never be as good as a display that considers angles of reflection and the interface between the LED package and your difusing medium.
Thanks, any idea what the material is that they use to diffuse the light emitted by the LED? Maybe an epoxy with a characteristic refractive index? I'm happy to experiment.

I'm trying to make displays with unconventional shapes (perfect circle transected by 2 lines, for example).

thanks!

#### dl324

Joined Mar 30, 2015
12,223
any idea what the material is that they use to diffuse the light emitted by the LED? Maybe an epoxy with a characteristic refractive index? I'm happy to experiment.
It's a glass filled epoxy resin with the color chosen chosen for optimal optical transmission based on the wavelength of the LED die in question.
I'm trying to make displays with unconventional shapes (perfect circle transected by 2 lines, for example).
You might check with a company like VCC that sells light pipes to get some ideas. I've seen light pipes used in a lot of equipment. Sometimes they shape/difuse the light from a discrete LED; other times they bend the light 90 degrees.

You might also opt for a panel in front of the LED with a cutout in the shape you desire.