The drivers on WS2812B addressable neopixels are drawing current even when the neopixels are off, set to color 0 (no neopixels elements lit).
Under 1 milliamp per pixel, but with lots of pixels this could add up. It's also not so much compared to the current when they're active but certainly a major concern for a battery powered device.
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Step 1: WS2812B Reducing Power Consumption.
I use the circuit in my Rainbow Word Clock. https://www.instructables.com/id/Rainbow-Letter-C... It contains 168 neopixels and I measure 69 mA to the neopixels when they are all out. The neopixels are turned on by a radar sensor. As long as someone is around, the clock is on. Assuming that the clock is off 12 hours a day, total shutdown then saves: 5 (Volt power supply) * 69/1000 (Miliampere / 1000 = Ampere) * 12 (Number of hours per day) * 365 (Number of days in a year) = 1511 Watt hours. So on an annual basis 1.5 Kwh.
I agree, it's not much in itself, but many small ones make a big one.
The circuit is simple. The plus of the power supply is switched by a P-channel MosFet. I have put two MosFet parrelel to keep the ON resistance as low as possible due to loss of the MosFets. In normal use I measure 4.5 mili volts over the MosFets. The gate is controlled by an output from the Arduino via a 470 Kohm resistor. If the output goes to low (0) digitally, the neopixels are on and at a high (1) they are off.