"...guideline of operating at less than 60% of the rated power."

[vervdesignDOTcom]

Great parallel/series LED calculator.
Question: Does the statement "The wizard picks a resistor wattage for you based on the guideline of operating at less than 60% of the rated power." mean that my LEDs will not be at optimum brightness? Why would I want my LEDs at "less than 60% of the rated power"? Is that the guidline to balance brightness and lifespan?

If I went from a 1/2 watt resistor to a 1/4 would that increase brightness?

Thank you!

[justDIY]

all that means is the wizard picks a resistor that is 'beefy' enough to handle the wattage dissipated

for example ... lets say your calculations come out to the resistor needing to dissipate (burn off!) 240 milliwatts ... well, a 1/4 watt resistor can handle that, but it's not a very large margin in case of surges, etc...  so the wizard in this case would recommend a 1/2 watt (500 mw) resistor

the LED's brightness is controlled by the ohms value (the resistance of the resistor) ... so try to find a resistor that is as close as possible to the actual calculated resistance required ... for example, your calculations come out to needing a resistor that is 88 ohms, but since there aren't any that size, the wizard recommends 100 ohms ... well, this means your led won't quite receive the exact power you intended, but it's pretty close ... if being exact is important, larger supply houses like Digikey and Mouser carry resistor series that basicly cover every resistance from 1 to 1 millon, so you could order an 88 ohm resistor in that case, but they will certainly cost more

[Rob]

The guideline affects the resistor sizing only.

Resistors come in standard power ratings: 1/8W, 1/4W, 1/2W, 1W, and 2W are common sizes. The 60% guideline is what I apply to pick the appropriate resistor. So if the wiz calculates you're dissipating 299mW in your resistor, he'll let you get away with a 1/2W, but at 300mW you'll get a recommendation to use a 1W.

This has no effect on the current delivered--it's just a matter of being conservative when selecting a resistor that will last a while. I also include the calculated power and publish the 60% guideline in case you feel like being less conservative. For example, if you can find a 1/2W but not a 1W resistor of the value you need in the 300mW case above, it's probably okay to go with the 1/2W.

And welcome to the boards.
( I see JustDIY got a reply in ahead of me too, good job )