Which of these is the blue LED?  - Page 1
Forum section: electronics / beginners

author: NaDobraNich
author_rank: Regular Contributor
timestamp: April 01, 2024, 10:24:16 pm
content: LTST-E133I'm trying to determine which one of these three LEDs in this package is the blue one. The datasheet doesn't say.The spacial luminosity chart seems to show green is in the center.So is the red AlGan one on the right? Or is that the blue that has different construction from other LEDs?Better image:https://www.mouser.com/images/liteon/lrg/LTST-E133CEGBK_SPL.jpg

author: Zero999
author_rank: Super Contributor
timestamp: April 02, 2024, 07:44:49 am
content: Yes, the red one is the red LED. Unfortunately there's no way to differentiate the green from the blue, without turning it on.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 02, 2024, 09:03:44 am
content: The blue LED is the blue one.As shown in the datasheet, R stands for red, G stands for green, and B stands for blue (page 12 of 14):https://optoelectronics.liteon.com/upload/download/DS22-2020-0083/LTST-E133HEGBK.PDF

author: MrAl
author_rank: Super Contributor
timestamp: April 02, 2024, 10:13:07 am
content: Quote from: NaDobraNich on April 01, 2024, 10:24:16 pmThis looks right, partly from the data sheet...

author: wraper
author_rank: Unknown
timestamp: April 02, 2024, 10:24:44 am
content: Red one is obvious. And according to spatial distribution it should be this:

author: cosmicray
author_rank: Frequent Contributor
timestamp: April 02, 2024, 10:30:34 am
content: Many of the common variety 2.5-3.5 v LEDs will illuminate from the diode test on a DMM. The cheap DMM I'm using will also cause them to flash on the capacitance test ranges (lower capacitance range gives a dimmer flash, higher gives a much brighter flash).

author: pcprogrammer
author_rank: Super Contributor
timestamp: April 02, 2024, 12:21:35 pm
content: Quote from: cosmicray on April 02, 2024, 10:30:34 amOnly issue here is that this is a digitally driven RGB LED assembly. Only way to verify the datasheet on validity is to hook up the power supply and send the data to illuminate the blue LED.

author: CaptDon
author_rank: Super Contributor
timestamp: April 02, 2024, 01:07:42 pm
content: MrAl provided the datasheet and from that it is obvious which LED is R/G/B as it also shows the orientation of the device. Strange that one LED is constructed so differently than the other two however the luminousity intensity and field pattern are very well matched so they had their reasons.

author: wraper
author_rank: Unknown
timestamp: April 02, 2024, 01:25:18 pm
content: Quote from: CaptDon on April 02, 2024, 01:07:42 pmNot strange at all. Blue LEDs always have two bond wires due to how die is grown on sapphire substrate. There are no red InGaN LEDs in production, so it's not necessary making two bond wires for those.

author: NaDobraNich
author_rank: Regular Contributor
timestamp: April 02, 2024, 05:23:01 pm
content: Quote from: MrAl on April 02, 2024, 10:13:07 amSo....I should have pointed this out because it isn't obvious. But this picture is likelywrongunreliable. Because the pin out is wrong. This is a generic picture, so I would not take into account that has to be the order of the LEDs.

author: NaDobraNich
author_rank: Regular Contributor
timestamp: April 02, 2024, 05:24:05 pm
content: Quote from: wraper on April 02, 2024, 01:25:18 pmThis is what I was looking for! I knew someone would be able to look at it and confirm based on the different construction. I had assumed the odd-man out was the red one, and green we know is in the center.

author: MrAl
author_rank: Super Contributor
timestamp: April 03, 2024, 09:18:05 am
content: Quote from: NaDobraNich on April 02, 2024, 05:23:01 pmThat's almost always the case anyway as every design has to be bench tested at least once, preferably more than once. An overnight run is also recommended if this is to go into production.If the placement is that critical then it also be necessary to contact the manufacturer to make sure they will never change the arrangement of LEDs for this very part number. These days they do things that that too. They even change the pin marker sometimes and you don't know it right away.