Under-driving led

[gblaszczuk]

What would happen if I drive 3W 700mA with a 500mA controller? Would the leds not be as bright? Would pwm be impacted in any way?

I have some 500mA Meanwell LDD controllers and don't want to spend more money on new controllers.

Thanks for help!

 

[sleepydoc]

Yes, they will be a bit dimmer. You should be able to look at the data sheet for the LEDs to determine how much of a difference it makes. They will also run cooler d/t lower power consumption. (some companies intentionally do this to extend the life of the LEDs.) I don't think PWM will be impacted.

 

[Bootlegger]

You will do nothing to your LED by running it lower than it's peak rated power. Basically, you're doing the equivalent of driving your car below it's maximum speed. LEDs only require a minimum forward voltage and drive current. Anything over will increase output until you reach it's maximum rated current. 500mA is half the current your typical premium LED will run at. Most LEDs in the aquarium world are rated to perform best between 500-700mA with the pricier ones going much higher, e.g. CREE.

 

[oreo57]

What would happen if I drive 3W 700mA with a 500mA controller? Would the leds not be as bright? Would pwm be impacted in any way?



Thanks for help!

Generally speaking your "lumens/watt" (LED's have a tendency to get more efficient at lower drive currents) will increase but your gross output will decrease (less overall lumens). To equal the gross output just increase diode count..
In other words it is somewhat better to underdrive and increase diode count than to overdrive w/ fewer diodes..

And of course your ind. diodes will remain cooler.

 

[stephenhall1987]

Under driving the LEDs with the amps is the same as dimming them with a controller. You do want to match your voltage. Most 3w LEDs run at 3 to 3.5v. You will add the voltage together for each LED in a series string. The Amperage in a series circuit stays constant.

 

[oreo57]

Under driving the LEDs with the amps is the same as dimming them with a controller.

err yes and no.... Taking a 1000mA driver and setting the "dim" to 50% means the LED will see 1000mA 50% of the time it is on.

Using a 500mA driver and running at 100% it will see 500ma all the time..

To your eyes it is the same, approx..but to the LED it is quite different..

Running said 500mA driver at 50% means it will still see 500mA but at half the time..

to be honest I have no idea which is "better" if one really is better. Of course sometimes one wants to got to "11"..


as to CREE, "overdriving" or reaching Max spec alo causes a "loss" of efficiency..

An overdriven LED, running near its maximum temperature produces only 68%* of the light output! (*For white LEDs. Royal LEDs produce 78% of the light at maximum temperature.) So, to continue with our previous example, let’s assume that the LED driven at 350 mA can be kept under 50 C, and it is producing better than 95% of its rated flux of 107 lumens (let’s say 102 lumens). Now we’ll overdrive it to 1000 mA. Cree says we can expect to achieve about 220% the rated output, but this assumes that the junction temperature remains at a very cool 25 C. From our experience, this is impossible to achieve at this current. Even with very agressive cooling and a large heatsink, you can expect to see junction temperatures of 75-100 C at this current, reducing your 220% expectation to a less compelling 176% increase.

 

[zachts]

To add to oreo57's response, if you only need 50% output from that 1000mA driver then using the 500mA driver at 100% output is better on all accounts. Lower heat, and also greater efficiency. You will get more light from the 500mA driver at 100% than you will at 50% from the 1000mA driver. These are small differences but on larger arrays add up in a hurry, particularly the difference in heat output. Generally not something to worry about on a DIY but good engineering equates to a good DIY.

That said those LEDs the OP is using are only rated for 700mA running them at any dimming level from a 1000mA driver will be OVER-DRIVING them and will shorten their life span and reduce efficiency greatly. Also if they are the older type "bridglux" style buttons then they really should never be operated long term above 500mA and expected to last long.

Using more LEDs and "under-driving" them is always the better option!