Low powered LED indicators - Page 1
Forum section: electronics / projects

author: Rachie5272
author_rank: Regular Contributor
timestamp: June 02, 2016, 07:11:46 am
content: I keep seeing mentions of how modern efficient LEDs can run on current as low as a couple milliamps, but I have yet to encounter any. Can someone point out a few coloured SMD indicator LEDs? I'm hoping to save power in my next project.

author: Fungus
author_rank: Super Contributor
timestamp: June 02, 2016, 07:18:39 am
content: Grabanymodern LED, pass 1mA through it and you'll see some light.

author: mariush
author_rank: Super Contributor
timestamp: June 02, 2016, 07:59:46 am
content: Just go to a distributor like Digikey and search through almost 21000 leds, filter by test current or typical voltage drop etc etc :http://www.digikey.com/product-search/en/optoelectronics/led-indication-discrete/524729Here's a 0402 that can work at 1mA or less :http://www.digikey.com/product-detail/en/rohm-semiconductor/SML-P11MTT86/511-1652-6-ND/2036467And here's a 0603 super red that should be quite bright at 2mA or less and should still be solderable by hand without magnifying tools :http://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/LS-L29K-G1J2-1-Z/475-2506-1-ND/1802633

author: Fungus
author_rank: Super Contributor
timestamp: June 02, 2016, 08:22:29 am
content: Quote from: mariush on June 02, 2016, 07:59:46 am'Test current' isn't "the lowest possible current that will produce light", it's "the lowest current where we bothered to plot data on the datasheet".Only a very tiny fraction of those 210000 LEDs won't produce enough light to function as a 1mA indicator LED, if any.(...assuming you look for 20mA LEDs with a human-visible output wavelength. Do I really have to state the obvious?)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 02, 2016, 08:37:46 am
content: White is a good choice if voltage allows. Else HE red

author: zlymex
author_rank: Frequent Contributor
timestamp: June 02, 2016, 12:47:47 pm
content: Modern LEDs have very good linearity, the light output is proportional to the current when the current above as low as a few uA.Therefore, buy the brightest LED.

author: alank2
author_rank: Super Contributor
timestamp: June 02, 2016, 12:51:34 pm
content: So I admit to frustrating one of the packing guys at either mouser or digikey, I literally ordered qty 1 of probably 50 LED's to try out because I was frustrated with ordering one only to find that it takes 20mA to barely see it. It is all about the TYPE of led it is, and each color has its best type. I've standardized on using these:APT2012CGCK for greenAPT2012SURCK for redBoth are very bright for the amount of current you put through them. You can get them in different sizes as well, just change number but stick with the CGCK or SURCK.Edit to add - also you may find that pulsing them will make them look brighter for less power. I never bother though.

author: dannyf
author_rank: Super Contributor
timestamp: June 02, 2016, 01:06:58 pm
content: Quote1ma can get pretty much any LED to light up, reasonably brightly.It is not unusual for an LED to remain visible below 100ua or even 10ua, especially the super bright blue ones.

author: ebclr
author_rank: Super Contributor
timestamp: June 02, 2016, 01:20:14 pm
content: If is for human eye to see even a regular LED can work with less than 1ma avg.Just play with vision persistence, and send a pulse of 3% duty cicle

author: tszaboo
author_rank: Super Contributor
timestamp: June 02, 2016, 01:25:34 pm
content: Just order those which are marked as "circuit board indicator" and you are probably good to go. And dont use blue or too bright white.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 02, 2016, 01:33:13 pm
content: Quote from: alank2 on June 02, 2016, 12:51:34 pmThink you swapped those part numbers

author: Siwastaja
author_rank: Super Contributor
timestamp: June 02, 2016, 01:33:26 pm
content: If shopping green LEDs, use wavelength as a first-order approximation. 520-530nm LEDs, sometimes marketed as "true green" or something similar, can be 10x more efficient than more traditional, yellowish green LEDs (at about 560-570 nm). Added benefit is that they are easier to distinguish from yellow even for people with good sight, let alone those with red-green color blindness.But what's wrong with just sorting the products using the candela output? Assuming standard indicator LEDs, they are almost always tested at 20mA, so you can have direct comparison. Pick the brightest, and it will be the brightest at lower current, too, because LEDs are linear.

author: RogerRowland
author_rank: Regular Contributor
timestamp: June 02, 2016, 01:45:26 pm
content: I guess you also need to watch this:https://youtu.be/TJcMgoJ4DOE

author: alank2
author_rank: Super Contributor
timestamp: June 02, 2016, 01:58:04 pm
content: Quote from: mikeselectricstuff on June 02, 2016, 01:33:13 pmYes I did; thanks. Fixed it!

author: ataradov
author_rank: Super Contributor
timestamp: June 02, 2016, 05:50:58 pm
content: For RGB LEDs I can highly recommend Creehttp://www.digikey.com/product-detail/en/cree-inc/CLV1A-FKB-CK1N1G1BB7R4S3/CLV1A-FKB-CK1N1G1BB7R4S3CT-ND/3990811They are designed for outdoor displays, so they are blindingly bright at their rated current, but at 500 uA - 1 mA they have perfect brightness for indication LEDs.

author: retrolefty
author_rank: Super Contributor
timestamp: June 02, 2016, 06:27:02 pm
content: Quote from: Rachie5272 on June 02, 2016, 07:11:46 amMost all Arduino boards use 1K series resistors to drive the 2 on-board LEDs and they are quite bright.

author: Someone
author_rank: Super Contributor
timestamp: June 03, 2016, 03:01:48 am
content: Quote from: zlymex on June 02, 2016, 12:47:47 pmDo you have some data to back that up? The light is proportional to current, but not very linear for most LEDs especially down into nA where leakage dominates. Here you can see linearity across the range above 1uA:https://www.eevblog.com/forum/blog/eevblog-869-counting-led-photonsQuote from: Siwastaja on June 02, 2016, 01:33:26 pmCandela is proportional to the viewing angle, so it is hard to quickly compare large numbers of parts. But Digikey offers easy downloading of their catalog searches so its possible to evaluate computed metrics offline.

author: Mr.B
author_rank: Unknown
timestamp: June 03, 2016, 03:10:51 am
content: Quote from: ataradov on June 02, 2016, 05:50:58 pmI use these CREE ones all the time now for RGB PCB indicators.The first time I designed them into an RGB clock face I looked at the rated 20mA on the datasheet and thought I will de-rate to 15mA and it should be fine.After testing... De-soldered all resistors... Replaced... Now I design to draw 1mA max.

author: coppice
author_rank: Super Contributor
timestamp: June 03, 2016, 04:27:24 am
content: If you need low power panel lamps, you can get red ones that are bright enough for most purposes at <100uA. They cost a little more. We have some applications where most of the LEDs are powered from the mains, but a couple need to be powered long term from a weak energy source. We use cheap LEDs at a few hundred microamps for the mains powered ones, and a couple of slightly more expensive LEDs at 70uA-100uA for the ones powered from the low energy source.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 03, 2016, 05:47:35 am
content: Quote from: Someone on June 03, 2016, 03:01:48 amThis was not about nanoamps, but about LED indicators at "a couple milliamps".Any indicator LED is not only "linear enough", but even better, slightly non-linear to the right direction -- more light for the current -- down to way less than 1 mA.

author: Someone
author_rank: Super Contributor
timestamp: June 03, 2016, 07:39:30 am
content: Quote from: Siwastaja on June 03, 2016, 05:47:35 amIts not idle chatter, you should really look at the quoted data:Quote from: Someone on June 03, 2016, 03:01:48 amWhich shows efficacy dropping consistently as the drive current reduces down from 10mA, the opposite of what you claim. I've not seen any small LEDs (optoisolators, IR LEDs, anything) datasheets showing a sustained increase in efficacy at lower drive currents.

author: John Heath
author_rank: Frequent Contributor
timestamp: June 03, 2016, 10:51:06 am
content: There is a degree of superficial salesmanship in all electronic projects. As In cooking it is all in the presentation. In the interest of this there can never be too many LEDs. More is always better to razzel and dazzel on lookers. Pre power supply needs a LED , regulated 5 volt LED , anything that changes less than 10 times a second must have a LED regardless of the relevance of this information. I say use a bigger battery , nicad rechargeable , to support 10 LEDs at full brightness , 20 ma , all blinking and flashing to give your electronic project come alive with punch.

author: Fungus
author_rank: Super Contributor
timestamp: June 03, 2016, 11:42:49 am
content: Quote from: Someone on June 03, 2016, 07:39:30 amI think that data is for a phosphor based LED.(I'm not saying that efficiency will increase at low current, just that that data may not be applicable to all LEDs).

author: Rachie5272
author_rank: Regular Contributor
timestamp: June 03, 2016, 11:00:39 pm
content: How do various viewing angles compare when using a bezel or mask in front of the LEDs? I'm intending to have a sheet of painted acrylic over the LEDs, with small unpainted circles to let light through. I get the feeling a narrow viewing angle would be better to avoid light leakage through adjacent circles.I'm limited to 500 mA on USB power, so I can't quite have enough LEDs to make a simulated sun. Unfortunately.

author: Buriedcode
author_rank: Super Contributor
timestamp: June 04, 2016, 11:41:51 pm
content: Just to add to all the replies.I added a bunch of 'novelty' LED's to an order to make up fro free delivery. Got a few of these:http://www.rapidonline.com/truopto-osg74l3131a-3mm-fluorescent-green-colour-led-55-9161They are intolerable at 5mA. Still bright at 2mA. In low light (evening, couple of lamps in a room) it lights dimly when touching each of its legs. (that reads very awkwardly..). There have been 'low current' LED's around for as long as I've been designing stuff which don't seem to change in brightness much from 3mA up, so much so that '1k' is my standard current limiting resistor for them.For panels, 'clear' LED's are rarely a good idea, whilst defused can appear lit in bright conditions. For years I've tried to use diffuse milky white housings for coloured LED's, specifically bicolour red/green to reduce the number of panel holes required and for a dynamic interface.