Question

which led bulb has a lower forward voltage?

Explanation:

In general, the forward voltage of an LED depends on its color. Red LEDs typically have a forward voltage in the range of 1.8 - 2.2 V, while blue LEDs usually have a forward voltage around 2.4 - 4.0 V (depending on the type, but generally higher than red for common small - signal LEDs). So, the red (orange - hued in the image, likely red - based) LED bulb has a lower forward voltage.

Answer:

The orange (or red - like) LED bulb (the lower one in the image) has a lower forward voltage.