Can you put a dimmer on LEDs?

[Um...Me123]

Sorry this is another really easy question.  Can you put a dimmer on LEDs or is there no "space" (for lack of a better word) between when they have enough voltage to light up and their max voltage?

[ECET0purdue]

you can put a potentiometer between the voltage and the led and it will dimm and get brighter...just rember too bright and then POP....no more led..
cheers
glen

[audioguru]

An LED is a diode with a fairly constant voltage across it, not a resistive hot piece of wire like a light bulb.
LEDs operate with current, not voltage. A supply voltage higher than the LED voltage is used and the current is limited with a current limiting resistor in series with them. The lower the resistance then the higher the current and brightness.
A potentiometer to limit the current wastes a lot of power and might over-heat the potentiometer. Duty-cycle control by pulse-width-modulation is frequently used to dim LEDs efficiently (without much wasted heat). A high current is pulsed through the LED at a frequency high enough so that you don't see flickering and the duty-cycle of each cycle's on time vs its off time changes the brightness. ;D

[MP]

It would be a fairly uncommon circuit to generate heat at this point with a standard LED. Any circuit which normally uses a resistor as a current limit to the LED can use a pot to adjust the brightness. Don't forget to use a resistor in series with the pot, because the pot will allow zero resistance at one end. This has no more effect on this circuit than changing the resistor to a different value for the same purpose. Just remember to calculate the current min and max and use correct ratings of resistor and pot (you do know the formula for calculating LED resistor, right?) 

From a manufacturing point of view, it would be a waste of components and board space to make a pwm circuit to adjust the brightness of a panel light.

MP

[Um...Me123]

So as long as the pot is after the resistor I'm ok?  Sorry guys I know almost nothing about this stuff.  Yes I do know the calculations and I'm using the LEDs to light the interior of my boat (not panel light) and I'm not using a curcuit board of any kind.

[Guest Alun]

In this case I think PWM is the best solution as using a current limiting resistor or power transistor might require an large expensive heatsink - it depends on the LED current, voltage drop and power supply voltage.

How much current does you LED require?

What's the forward voltage drop?

What power supply are you using?

Or:
Does the LED have a built in current limiting circuit? Do you just connect it up to the power supply and it works?

[audioguru]

Sure Alun,
Um-Me just hooks-up his LED directly to his 12V battery with very thin connecting wires. The wires smoke a little and the LED is so blinding bright that he needs a dimmer for it! ;D ;D

[Guest Alun]

You may laugh audioguru, but some LEDs (I'm talking more about LED lamps/modules than discrete LEDs here) have a built-in resistor or constant current regulator - some modules even have built in switching regulators. ;D

If the LED is like this then you might be able to get away with using a normal PWM circuit even if it uses a built-in switcher it might still work but you'd better make the PWM frequency a small fraction of the switcher's or it won't work properly.

[Guest Alun]

This switching regulator discussed in this thread can be tweaked into an adjustable constant current source that could be used to dim the LED.

[MP]

Yes I do know the calculations and I'm using the LEDs to light the interior of my boat (not panel light) and I'm not using a curcuit board of any kind.

Does not sound like you want to use a pot, then. You need to look at the spec sheet for the LEDs you are using.  If you do not want to build a PWM controller or circuit on a board to control this, you might be able to get by with a car headlight dimmer. You might get more useful ideas than this if you could draw your schematic and let everyone know the part numbers of the LEDs. There is a lot of electronic experience here at your fingertips. You should post your diagram.

MP