Voltage divider producing unexpected voltage
Since you are connecting your pixel strip in parallel with R2, the
correct formula is

Vout = Vin × (R2∥Rp) / (R1 + (R2∥Rp))


Where Rp is the resistance of the pixel strip and

R2∥Rp = R2 × Rp / (R2 + Rp)


is the combination of R2 and Rp in parallel. From this you can see that
an output voltage of 1.6&nbsp;V is consistent with a strip resistance of
300&nbsp;Ω.

This is, however, somewhat oversimplified, as the I(V) characteristic of
the LED strip is probably non-linear, thus not really equivalent to a
resistor.