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post #22 of (permalink) Old 01-23-2013, 11:23 AM
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Join Date: Jul 2003
Location: Charlotte, NC, USA.
Posts: 188
V=IR and P=IV (I=current, V = volts, R = resistance, P = power).

Yes, the CREEs can be more efficient. That's why they are more expensive.

I don't know how linear the LEDs are with regards out input and output. Resistance can change. My general guess is they are somewhat linear until you get near max output, and then they saturate. Extra additional input equals to less additional output.

Originally Posted by ced281 View Post
Anyone know how to calculate the lumens per watts for these? Will a 5W Cree really run at 5W if you're only running at 700mA instead of it's max 1.5A?

From back in my high school days, P=IV so Power = Current * Voltage. I'm assuming that the voltage doesn't change for these guys so if you decrease current the power (wattage) should decrease proportionally.
> So the power consumption of a 5W Cree running at 700mA is closer to 2.3W.
> Which means the lumens per watt is ~113
> Whereas the lumens per watt of these "high-power" Chinese LEDs are ~60 (180lumens/3W)
> Which means the efficiency of the Crees is almost 2x!
Does that make sense???
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