I asked how much resistance was required before two LEDs in series. After a response, on how to do it, i worked out that i needed. I have worked out two values of resistance needed to be 48 and 66.67. I am thinking of using a 47 ohm resistor and 68 ohm resistor. Is that fine
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\$\begingroup\$ Why not copy the context into your question rather than just posting a link to it? \$\endgroup\$– jippieCommented Feb 8, 2016 at 18:44
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2 Answers
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It's more than fine. LEDs don't change that much in visual brightness with the resistor value. Heating will increase, however, so it's safer to use a bit higher value than the minimum (the next higher value in the E24 series than that required for your nominal current would be a reasonable choice- assuming the latter is wisely chosen).
I doubt you'd see much difference in visual brightness with 66.67 Ohms, 68 Ohms or 75 Ohms. The eye is better at matching so it's best to keep them all the same if there are multiple LEDs near each other- but individual LEDs will vary a lot in brightness from one unit to the next.
To get a 'feel' for it, get ahold of a bunch of values and compare for yourself. You may find you're happy with 150 Ohms or even 510 Ohms rather than 68 Ohms and you can save a bunch of energy, and extend the life of the LEDs- especially in a hot environment where running them at high current can truncate their useful existence. Indicator LEDs can easily be too bright.
answered Feb 7, 2016 at 13:53
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You don't need to be that precise with resistor value, after all you'll probably use 5% resistors. And you can use one resistor. Here's a tool that would help you out: Electronics assistant
But you really need to get familiar with your components.
