It depends. As with any other light, under broad daylight with direct sunlight, the lights will not be very visible. The darker it is, the more prominent the lights will be.
For the turn signals, you should always use hand signals and only use Lumos as a supplement to those, even at night. During the day this is especially true as your hand signals are readily visible. Please follow the rules of the road! That’s the best way to ride safely.