LED Alternatives - Page 1
Forum section: electronics / projects

author: ajp8868
author_rank: Regular Contributor
timestamp: February 16, 2023, 08:43:32 pm
content: Hi All,I'm struggling to find an LED that is suitable for a specific replacement (cheaply). The light in question uses an old CST-90-W65S and the company that makes them have a new replacement at ~£100 each. Sadly the lights are not even close to being worth that & I need 2. The original LED was 50w but that is no longer available anywhere.Now, I've found a few alternatives via AliExpress and I already had a 60w version from an earlier purchase that I tested, it lit for a second then it blew.I've checked the data sheets for the original and the maximum rated current on the original is 18a. All the 60w ones are only rated for 14a max.My question is, can i replace it with one of the "80w" ones that are rated for higher amps, because the driver is constant current?Thanks!

author: kreyszig
author_rank: Regular Contributor
timestamp: February 17, 2023, 07:13:47 pm
content: Quote from: ajp8868 on February 16, 2023, 08:43:32 pmIt sounds like a reasonable assumption to begin with, but maybe you should verify the specs around the thermal requirements for the 80w ones vs your original 80w LED if possible?

author: james_s
author_rank: Super Contributor
timestamp: February 17, 2023, 07:16:09 pm
content: The original LED you linked to is only 1,000 lumens, with modern tech that should be around 8 watts, nowhere near 50W. Have you looked at current offerings by Luminus? You could also check out Cree.

author: shapirus
author_rank: Super Contributor
timestamp: February 17, 2023, 07:37:53 pm
content: what current is the LED driver set for? is it adjustable/can it be replaced? you'll need to take this into account when searching for a replacement LED.

author: ajp8868
author_rank: Regular Contributor
timestamp: February 20, 2023, 06:15:30 pm
content: The driver is OEM in a disco light - it has a small POT so I'm guessing it's adjustableI've tested today and it's outputting 14a. The LED I've tried so far was only rated to 12 (obviously that's why it went pop)I've ordered some that are rated for 14 so hopefully they'll do the job. I'll attempt to reduce the current slightly too with that POT as I think the originals were rated for 18a and under-driven (although they blew so maybe not..?)

author: james_s
author_rank: Super Contributor
timestamp: February 20, 2023, 07:21:32 pm
content: If you can find an LED rated for 18A or even more, it will last longer and operate at higher efficiency if it's only being driven at 14A. It's always acceptable to under-drive an LED, just make sure it has a similar forward voltage and is mechanically compatible. In your case I doubt the higher brightness resulting from a more modern LED will be a problem, more likely it will be an improvement.

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2023, 07:55:10 pm
content: modern diodes rated for 14 A can be so bright that they'll blind you before you understand what happened (and burn themselves shortly after, if not properly heatsinked -- that's going to bea lotof heat to dissipate). be careful.that's why I was asking about the driver's output current. to produce 1000 lm, a modern LED will only need a few watts of power, and if the driver can be adjusted down to source just a few amps, then, with a smalled LED, it might be the way to go.

author: james_s
author_rank: Super Contributor
timestamp: February 20, 2023, 08:06:31 pm
content: The old ones will get even hotter because they're driven by the same current and produce less light. If the heatsinking was adequate for the original diode, it will be adequate for a more efficient replacement.

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2023, 08:20:52 pm
content: Quote from: james_s on February 20, 2023, 08:06:31 pmThe amount of energy carried away with light is negligible (in this context), it will not really make any difference.Speaking of heat sinking, it's the possible difference between the voltage drop across the old and new diodes at the same current that has to be paid attention for. If, for example (I have no idea of the actual values) the old diode had a drop of 2V @14A and the new one will have 3V @14A, then the difference will be (almost) 14W between the two. This is something to keep in mind: it's possible that the new LED will require current to be adjusted lower still.

author: ajp8868
author_rank: Regular Contributor
timestamp: February 20, 2023, 09:24:53 pm
content: It does have quite a beefy heatsink and fan. I don't think cooling will be too much of a problem. I think it's only been a problem with this one because the vents were blocked with lots of badness..Here's the datasheet of the original LED (I guess you'd call it an array as there's multiple diodes?)https://www.mouser.co.uk/datasheet/2/245/luminus%20devices_luminus_cst90_binninglabeling-1177369.pdf

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2023, 09:28:02 pm
content: Quote from: ajp8868 on February 20, 2023, 09:24:53 pmnot really a datasheet, just binning and labelling info.

author: ajp8868
author_rank: Regular Contributor
timestamp: February 20, 2023, 10:14:29 pm
content: Quote from: shapirus on February 20, 2023, 09:28:02 pmFound the right onehttps://media.digikey.com/pdf/Data%20Sheets/Luminus%20PDFs/CST-90.pdf

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 21, 2023, 12:12:52 am
content: I'm not very impressed by that Luminus led. 100Lumen/Watt is nothing impressive these days, you can go over 200lm/Watt with modern LED's. And that value is only specific at 3.15A, and with higher currents efficiency goes down.Quote from: shapirus on February 20, 2023, 08:20:52 pmThat used to be a valid rule of thumb, but efficiency of LED's has improved so much over time that it is not true anymore. The theoretical maximum is 683lm/W and LED's with 200lm/W are creeping towards 30%. The numbers are not accurate though, for example light color is an important factor in LED efficiency, and it's omitted for simplicity.https://en.wikipedia.org/wiki/Luminous_efficacy

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2023, 03:09:30 am
content: Quote from: Doctorandus_P on February 21, 2023, 12:12:52 amThe key phrase there is "these days". The LEDs offered by Luminus were top notch at the time. IIRC they were the first on the market to reach 1,000 lm and again to reach 2,000 lm from a single LED.

author: DavidKo
author_rank: Frequent Contributor
timestamp: February 21, 2023, 07:53:17 am
content: To get the same lumen output, with new LEDs you can go lower with the current. As mentioned before, new LEDs are more efficient. It will mean cheaper power supply and less heat from the LED to be cooled.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2023, 08:34:16 am
content: Quote from: Doctorandus_P on February 21, 2023, 12:12:52 amThat's true, especially for some red and violet LEDs, which can have efficiencies exceeding 50%. 30% seems reasonable for white given some of the energy from the blue LED is lost in the phosphor.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2023, 09:52:03 am
content: Quote from: ajp8868 on February 20, 2023, 10:14:29 pmVf looks quite typical to me, which is a good sign.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2023, 09:53:39 am
content: Quote from: Doctorandus_P on February 21, 2023, 12:12:52 amWow did I miss the progress in this field.Well, good to know.

author: DavidKo
author_rank: Frequent Contributor
timestamp: February 21, 2023, 09:57:38 am
content: 1000lm are the usually cold lumens (25ms pulse measurement) and the stable light output can go down 15%@150°C junction temperature which means lower temperature on the heatsink (depending on thermal resistance to ambient). There are also derating curves for different ambient temperatures and Rth in datasheet which needs to be followed to prevent LED damage (or lower lifetime).Edit: it is not so easy to find the replacement LED - you need to have similar (better) thermal parameters or run it at lower current (it can still have same light output). Light distribution and chip size should be similar depending on the optics used in front of LED.

author: Zero999
author_rank: Super Contributor
timestamp: February 25, 2023, 09:55:04 pm
content: Quote from: shapirus on February 21, 2023, 09:53:39 amIt's truly amazing. Here's a link an IR LED with an efficiency or over 50%.Radiant power = 2.58W. VF= 6.83V, IF= 700mA. PIN= 6.83*0.7 = 4.781W. Efficiency = 2.58/4.781 = 54%https://dammedia.osram.info/media/resource/hires/osram-dam-23870254/LZ4-00R408_EN.pdfA white LED won't be as efficient, but will still radiate a good proportion of the power in as light.