The ineffectivity of upper light guides on part 553-3937-ND

We have incorporated part 553-3337-ND, but there seems to be a significant difference in the brightness between upper and lower leds. In the picture you see the difference clearly. All the leds have the same conditions: 3.3V/330 ohm. The brightness difference remains if we raise the power. It looks like the light guides loose the effectivity where they bend 90 degrees between the back side and top.
Is this an expected result of this part?

Best regards
Jannick Madsen
KE Supply A/S


I am not seeing information that indicates that it is meant to be that way.
I will submit an inquiry to see if the manufacturer has insight.

Hi sa1

Below is what we received from the product specialist.

Can you verify the part number? Are they asking about part 553-3337-ND? Because the images below are not of part 553-3337-ND, but they are actually of part 553-3937-ND. Is that the part they are asking about?

It’s about Part 553-3937-ND

Yes: a light guide achieving a 90° bend in this matter will leak substantial light at the bend point. Note that the datasheet for the product in question gives indicator specifications “per vendor’s specifications,” indicating that they’re simply repeating the data from the LED manufacturer rather than specifying behavior at the output of the light pipe.