Help with power control and source. Alarm clock w/ high power LED


So I'm trying to make an alarm clock that has a light that fades in before the alarm buzzer (faux sunrise, obviously less bright, to make waking up easier). So I'll need a high power LED (either one or two 3W, currently thinking one will do the job). I'm struggling with how I want to control the power and what to use to supply it.

CONTROL I know led's have limited dimming capabilities but trying to use what is there. I originally thought transistor but from what I know they are like a switch and I wont be able to get a fade action. But I saw this video ( and he has the LED fade and now I'm confused because everything I've researched says they are like a switch. Mine will only be a warm white not RBG if that influences anything. Second thought was using a variable resistor but I don't have any experience with them (nor with transistors but they seem more simple). Thinking about possible power usage it would need to be a 1-5W rated resistor depending on the power supply.

Both would be activated by the arduino. Also a product recommendation would be helpful or at least what to look for in a product specs and what not.

SUPPLY So I originally thought I would use the arduino wall adapter and splice in a set of wires for the LED so they would run in parallel. Thinking about this more I don't think its a great idea as the adapter is meant to just power the arduino. But I would like to avoid having two wall outlets occupied for the one device. So now I'm thinking have the ardunio power adapter and a second adapter inside of the clock casing. Both adapters would be in parallel from an extension cord from the wall.

The LEDs I bought are warm light 3W 3.6-3.8V 700mA according to the product details.

If my idea is right about the two adapters a 5V 0.7A would be a good choice right? (found an old phone adapter in my dad's bin of out-of-date electronics). I'd need a 2Ω 1W rated resistor correct? R=V/I=(5V-3.6V)/0.7A=2Ω and P=IV=(5V-3.6V)*0.7A=0.98W. Or at the low end I think 2.5V should activate the LED 4Ω 2W

THANK YOU!!! I really appreciate the help.


led's have limited dimming capabilities

Um, No... When on only 1/1000 of the time they are pretty dim.

HERE is an example you can play with... You can change the code to be a "dimmer". |500x467

The 3W LED "Electronic Brick" shown there is really bright. It has it's own driver transistor so it's easy to use.

about the two adapters a 5V 0.7A would be a good choice right?

5V at 1 amp or more is good; more is better and it will only "take" the current it requires.

I don't think you want any resistors...

I hadn’t thought about flashing on/off at a high rate. I’ll give that a shot, Thank you.
Why wouldn’t I want a resistor? the forward voltage is rated at 3.8V not 5V. I don’t want to blow out my LED or burn it out prematurely.