If I have the LED & want it to light on a simple 12v circuit what else do in need please?
https://uk.rs-online.com/mobile/p/visible-leds/2285938/

 

You just need one resistor...

plus some specs and a little math so you can pick that resistor properly!

The key specs are the forward voltage (Vf) which is listed as 2.5V, and the forward current, which isn't listed anywhere.

It's pretty typical for small, generic LEDs like this to have a nominal operating current of 20mA, with a max of 25 or 30mA. The less current you run through it, the cooler it stays and the longer it lasts. Brightness is a function of current, but human vision is roughly logarithmic, so you can reduce current a fair bit with only small changes in perceived brightness. Many would say you should run this no higher than 10-15mA in order to extend its life, and I tend to agree.

Now for the calculations. If you have 12V total, and the LED is dropping 2.5V, that leaves 9.5V across the resistor. If you want 10mA of current (0.01A,) you can use ohms law to calculate the required resistance.

Resistance = Voltage / Current
Resistance = 9.5 / 0.01
Resistance = 950 ohms.

That value isn't common, but 910 ohms and 1k (1000 ohms) should both be readily available. If you prefer a different amount of current, use the example above and recalculate to choose a different resistor value.

Once you've got your resistor, just put it in series with the LED and you're all set - just don't forget to pay attention to LED polarity when hooking it up.

 

Thank you.
Something like this?
https://uk.rs-online.com/mobile/p/through-hole-fixed-resistors/6835616/

It's to run a small light on a scalextric car.

 

Thank you.
Something like this?
https://uk.rs-online.com/mobile/p/through-hole-fixed-resistors/6835616/

It's to run a small light on a scalextric car.

That is only a 1 ohm resistor. According to the calculations above you need 950 ohms (or even 1K). And at 12V you would only need a .5 watt resistor. (You might even get by with a .25 watt).

What you posted is 2W. Way over kill. It might not even fit in that car of yours.

 

Right, forgot to discuss wattage!

Heat dissipation in the resistor, measured in watts, is voltage across the resistor (not total system voltage) times current, so:

Wattage = Voltage x Amperage
Wattage = 9.5 x 0.01
Wattage = 0.095

Many people suggest over rating resistors by around a factor of two for reliability reasons, so:

Safer-Wattage = 0.095 x 2 = 0.19

So, 1/4W (0.25W) should be plenty large, even with a good safety factor. That's a very, very common size, maybe the most common in through-hole parts, so should be easy to find.

 

So it's this one?
https://uk.rs-online.com/mobile/p/through-hole-fixed-resistors/7077666/

Thanks for your help

 

So it's this one?
https://uk.rs-online.com/mobile/p/through-hole-fixed-resistors/7077666/

Thanks for your help

Yup, looks right to me!

 

I decided once to have all my lamps at the house changed. At first, I was pretty sure that everything will be pretty easy for myself, but then I found out that there are some issues because my house is damn old as a mammoth crap. Finally, I realized that I need professional assistance, and after two times of wasting my money on the guys just pretending to be the experts, I found the guys from electricianbrooklyn24. They really helped me and explained me what I was doing wrong. Those were different voltages and bulb sockets, as simple as that.

What does this have to do with the TS's issue?

 

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