Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

LED power rating question

Status
Not open for further replies.

evaine23

New Member
I've been looking at some 3W LEDs and I'm wondering where the 3W power rating is derived from? Using the absolute maximum forward current of 700mA and the max Vf of 3.5v i'm only calculating 2.45W and that is for a white LED with a high Vf. For a yellow LED with the same 3W power rating and a Vf of 2.6v i'm only calculating 1.82W. Those were calculated with the absolute maximum forward current. Using a forward current of 350mA which is what the wavelengths were anylized at, my calculated power outputs are halved. Are the power ratings just a class of LEDs such as anything grater than 1W and less than 3W is considered a 3W LED? It feels like i'm missing something here. Also, how much does the peak and dominant wavelenght of an LED shift when the forward current changes from say the 350mA used to calculate the wavelength and the 700mA absolute maximum forward current?
 
Most of the LEDs I use; the current X voltage get close to 3W.
Remember 3W is with a heatsink!

The white LEDs in a 3W case also come in red, green, blue, IR, etc. with different forward voltages.
My thought is that the case is "3W" and the higher voltage (white) LEDs are 3W. To make designing easy the IR version typically has the same package, the same current but different Vf and thus different wattage.

I have made flashlights what sold in several different colors and we only changed the LED, not the current regulator. (note I did not say voltage regulator)
how much does the peak and dominant wavelenght of an LED shift when the forward current changes from say the 350mA used to calculate the wavelength and the 700mA absolute maximum forward current?
That depends on the type of LED. A red LED will change very little over 2:1 current change. (any single color LED)
White LEDs are made in several different ways. I am using white LEDs that have phosphor over the silicon. (the LED excites the phosphor, much like a CRT monitor or florescent bulb). In this case the color of the phosphor changes (some) with current.
 
Thanks for the clarification. I'm putting together a constant current source to drive these and noticed that my calculations required something closer to a 60W supply while going by the power rating on the LEDs i would need something closer to a 72W supply.
 
Power rating,

I have a 60hp tractor. I have a car with a 60 hp engine. I also have a 60hp electric motor. There certainly is no comparison.

The tractor can pull some amount of load-distance-time that equals 60hp. Horse power at the hitch.
The car engine is much much smaller. The hp is measured differently.
The electric motor is stronger than the tractor.

In other words; A 3W LED is not a 3.000 Watt LED. It is in a 3W class along with some LEDs that are 1.5watt and have the same size case.
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top