Electronics > Projects, Designs, and Technical Stuff
Sourcing 5mm RGB LEDs for LED Cube
mark03:
--- Quote from: tooki on December 28, 2019, 11:33:09 am ---That makes no sense. Using PCBs blocks the view. Additionally, for an LED cube, you want a diffused LED body to blend the color of the 3 LED dice within the LED, as well as to provide a wide viewing angle. SMD RGB LEDs simply aren’t large enough for this blending to occur, even if they use diffused epoxy, and SMD LEDs tend to be much more directional than diffused THT LEDs.
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Wait a minute, surely you have this backwards? SMD LEDs have *wider* beamwidth than THT LEDs, not narrower.
The interconnect certainly become more difficult with SMD, but it has been done:
https://www.eevblog.com/forum/projects/kcube-led-cube-design-revisited/
tooki:
--- Quote from: mark03 on December 29, 2019, 06:49:14 pm ---
--- Quote from: tooki on December 28, 2019, 11:33:09 am ---That makes no sense. Using PCBs blocks the view. Additionally, for an LED cube, you want a diffused LED body to blend the color of the 3 LED dice within the LED, as well as to provide a wide viewing angle. SMD RGB LEDs simply aren’t large enough for this blending to occur, even if they use diffused epoxy, and SMD LEDs tend to be much more directional than diffused THT LEDs.
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Wait a minute, surely you have this backwards? SMD LEDs have *wider* beamwidth than THT LEDs, not narrower.
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Nope. I specifically (and repeatedly) said diffused THT LED. As in, with the milky body that changes it from a beam to just a glowing plastic blob. Very different from the water-clear LEDs that have (perplexingly) become the norm. A diffused THT LED can be seen even from well beyond 90˚ off-axis, even from behind.
--- Quote from: mark03 on December 29, 2019, 06:49:14 pm ---The interconnect certainly become more difficult with SMD, but it has been done:
https://www.eevblog.com/forum/projects/kcube-led-cube-design-revisited/
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Just because one can doesn't mean one should, and that thing is a perfect example thereof. Having to have transparent PET flex PCBs made, which then require an external frame to support them, and require low-temperature solder, turns that into a totally different type of project, and for what?
james_s:
The whole point of one of these LED cubes is to have a freestanding sculpture without any PCBs in the way. The bare minimum required to hold the LEDs in space. The only reasonable way for it to look right is to use through-hole LEDs.
mark03:
I didn't mean to suggest that one *ought* to use SMD LEDs for a cube; I merely took issue with the claim that they have narrower beam patterns. I still disagree with this. It is true that you can see THT LEDs from behind, but if you plot the actual brightness profile in the elevation (?) plane, I think they are still more focused than the wide-angle SMD type. For example, if you looked at the ratio of brightness, say, on axis and 70 degrees off axis, I think the SMD LEDs would still win.
tooki:
--- Quote from: mark03 on December 29, 2019, 11:54:57 pm ---I didn't mean to suggest that one *ought* to use SMD LEDs for a cube; I merely took issue with the claim that they have narrower beam patterns. I still disagree with this. It is true that you can see THT LEDs from behind, but if you plot the actual brightness profile in the elevation (?) plane, I think they are still more focused than the wide-angle SMD type. For example, if you looked at the ratio of brightness, say, on axis and 70 degrees off axis, I think the SMD LEDs would still win.
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I didn't say they have narrower beam patterns. I said they have a narrower viewing angle. And that's NOT the same thing! Why? Because a non-diffused LED is very nearly a point light source. In a water-clear THT LED (and many SMD ones), the body is a lens that focuses it in some way or another, depending on the design. But in a diffused THT LED, it's not a point source any more, it becomes a diffuse body, with little to no focused beam at all. The light output of a point source LED has a pattern that varies significantly by angle. In a diffused one, the angle is damned near irrelevant, and that's desirable. In an LED cube, you don't want the light output to be directional. 70˚ off-axis is still looking at the front of the LED. But in this application, you want an LED that is visible from well beyond that. An SMD LED, even wide-angle, will have little to no light output at or beyond 90˚, and even before then, you start to get color shifting as the LED housing blocks your line of sight to one or more of the individual LED dice.
You're thinking flashlights, where brightness is the main criterion. But in this application, the ideal would be a fluorescent sphere emitting all its light equally in all directions.
And again, you want the large diffuse body to provide a place for the colors to blend. Without this, much of the blending doesn't happen until the light beam hits a surface like a wall. Totally opposite of what you want in an LED cube.
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