From Brian Willoughby Sent Fri, May 3rd 2019, 03:24
(sorry to follow up my own post=E2=80=A6) Aiming for =E2=80=9Clower current use=E2=80=9D may create more of a = problem for you than it solves. I=E2=80=99d look at all of the variables = before deciding on the requirements. If you can=E2=80=99t find a data sheet, you could still use a meter to = measure the actual Forward Voltage drop of the original Moog LEDs. If = you can probe the resistors, you might be able to measure their = resistance, and from their voltage drop you can calculate the actual = Current. Those few measurements will allow you to select a modern LED by = looking at data sheets. The only thing that might be difficult is = measuring the color wavelength if you can=E2=80=99t find a =E2=80=9CSSL-22= =E2=80=9D data sheet with the nm spec. Unfortunately, there are many LED models that are almost completely = undocumented. Those that have a data sheet sometimes have very important = data missing. That said, there are still many brands and models to = choose from that have sufficient documentation. As I mentioned, a lot of it comes down to math, and you can probably get = very close. Once you have the data, you might actually be able to aim = for lower current use without things getting out of hand. Simple = equations like V=3DIR and the graphs of brightness versus current and = forward voltage versus current can help you predict the brightness. Brian On May 2, 2019, at 8:11 PM, Brian Willoughby <xxxxxx@xxxxxxxxxxxx.xxx> = wrote: > If this were my Polymoog ( ;-) ), I would try to find the model number = of the original manufacturer=E2=80=99s LED and look for a data sheet. = Hopefully, that data sheet would list the exact color wavelength of = those LEDs in nanometers. I would personally want the =E2=80=9Csame=E2=80=9D= color of red, not just any old red. >=20 > Modern LEDs are available in various shades, usually with good = documentation on the exact color wavelength. Of course, the really cheap = LEDs just say =E2=80=9Cred=E2=80=9D but you can still afford LEDs with = better quality control. Some have just a single wavelength, while others = have a wide range, but can still be =E2=80=9Cbinned=E2=80=9D by measured = wavelength in much narrower ranges. You could save a little money by = buying the unmeasured LEDs, but the savings isn=E2=80=99t worth the = tradeoff at your quantity. Instead, I think it=E2=80=99s worth paying a = little more to control the color. >=20 > Assuming you can find the original specifications (or perhaps measure = them), then finding a modern match should be easy. Most modern data = sheets have graphs showing brightness versus color, and you can match = the brightness as well. >=20 > As Murray pointed out, you=E2=80=99ll have to change the resistors, = too. The 180 ohm resistor sets the current, based on the LED supply = voltage and the LED forward voltage drop. If the modern LED has the same = voltage drop, then you=E2=80=99ll surely have to change the resistor to = get lower current. There=E2=80=99s a random chance that you could find a = modern LED with a higher forward voltage (that isn=E2=80=99t too high = for the existing LED voltage) and this would lower the current without = changing the resistor, but it seems unlikely that it would work out = precisely. >=20 > One option that you should consider is buying modern LEDs with the = same current rather than lower current. The reason for doing this is = that you wouldn=E2=80=99t need to change the resistors. Of course, = forward voltage and efficiency are factors. >=20 > One thing to note is that LED brightness can be measured in lumens or = candles, so you might have to convert between the standards if you want = to dial in the same brightness. Also look out for the dispersion pattern = - a directional LED will only be bright directly in front, while a = non-directional LED will spread out the brightness across a wider angle. = The difference between lumens and candles is related to dispersion in = different ways. >=20 > I suppose that I=E2=80=99ve made this sound like an incredibly = difficult task, but it=E2=80=99s actually quite simple if you do the = math. A good LED data sheet will give all the information you need to = calculate a match to the Moog original and perhaps even save you from = changing the resistors. >=20 > Good luck! >=20 > Brian >=20 >=20 > On May 2, 2019, at 1:51 PM, Dan Goldstein <xxxxxxxx@xxx.xxx> wrote: >> I=E2=80=99ve got a Polymoog I=E2=80=99m restoring, and I=E2=80=99d = like to replace the old, original LEDs with new, modern ones. The = originals were 5mm bulbs, =E2=80=9CSSL-22=E2=80=9D, each with a 180 ohm = resistor hooked up to it. >>=20 >> I=E2=80=99d like to replace them with new, modern red LEDs of = equivalent brightness and lower current use. There are so many different = LED values these days, and I=E2=80=99m not sure how to know what would = be the ideal replacement LED. Can anyone offer any advice on specs for = replacement LEDs for a Polymoog? >>=20 >> Thanks! >> Dan >>=20 >=20