LED brightness at 2.5W vs 5W: Does lumen output scale linearly with power?

Hi guys,
Quick question, I have a high brightness led light (350lm @ 5W) If I reduce the power to let's say 2.5W would the lm be cut in half or it won't work at all.

Second, since the LED light is rated for 5w would any combination of volts and amp be enough to power it, in other words is 5V 1A the same as 10V .5A when it comes to powering the LED or is there a specific voltage I have to look for.


Thanks

Hi Alejandro,

Technically, the brightness will vary if you only supply power of 2.5W only. It may not work on some instance, it really matters to know what it the required minimum power to drive the LED. Second, when we say power rating, it seems that if you simply combine a current and voltage rating just get the desire power your fine. But In reality, it matter to get the right current and voltage. The burden will be on the load(resistance), if you provide a high enough supply, the power drop will be wasted and turned to heat.

Hope it helps,
Kevin

Firstly, look at the data sheet. You have to supply sufficient voltage to get beyond the LED forward turn on voltage before current flows. An LED is a current controlled device once you get the voltage above that threshold, typically 1.5 to 4.5 V . At this point, the luminous intensity is proportional to the current flow.
See typical graphs for forward voltage and luminous intensity in the data sheet below.
http://www.farnell.com/datasheets/1678767.pdf
There are plenty of application notes and online calculators to help on biasing an LED, how to calculate the series resistor for a given power supply and forward current.
So to change the intensity you vary the current, with a power supply sufficiently above the forward turn on voltage that you get a sensible resistance value (watch the power dissipation in the led and resistor, they both have to handle the VI product). Power LEDs require good heat sinks.
At the power levels you are talking about, the best way to drive the LED is from a constant current output Switch Mode Power Supply, to keep power dissipation down.(efficiency up).
http://www.avagotech.com/docs/AV02-0532EN
gives some examples.
Cheers,
Richard

Hi,

Please checkout the following link.


http://addohms.com/ep8/



Regards

Amit