That all depends on the color or wavelength of the laser....and what you mean by "daylight" - cloudy or sunny day, shade or full sun....and atmospheric conditions - like clear air or humidity and fog. 532nm green is always the best bet per mw for visibility in any condition. On a bright sunny day you would have to have many, many watts of green to actually see the beam, and less on an overcast and foggy day. But either way you need a good deal of power to see a beam in broad daylight.