A simple question. Say I have a 24V power supply, a series string of 18 leds with a V(f) of 3V @ 500mA.
A popular calculator gives me this:
24V , 36W, 1.5A
Plus a standard efficiency cheat of adding 20%.
Do the resistor watts not err count?
Like use a 24V 45W 1.875A power supply?
What simple thing am I missing?
An online quote..
A popular calculator gives me this:
 6 series.3 parallel strings
 each 15 ohm resistor dissipates 3750 mW
 the wizard thinks the power dissipated in your resistor is a concern
 together, all resistors dissipate 18000 mW
 together, the diodes dissipate 27000 mW
 total power dissipated by the array is 45000 mW
 the array draws current of 1500 mA from the source.
24V , 36W, 1.5A
Plus a standard efficiency cheat of adding 20%.
Do the resistor watts not err count?
Like use a 24V 45W 1.875A power supply?

total power dissipated by the array is 45000 mW
What simple thing am I missing?
An online quote..
Take the length of your LED strip in feet and multiply it by the watts consumed per foot, then multiply by 1.2. This will give you the minimum sized power supply you'll need to run your strips.