One in the morning, another during midday, and a 3rd in the late afternoon.
Not to mention the many "bulbs" created by different sorts of cloud cover.
:stoned:

I doubt, however, it would effect the plants in any major negative or positive way.

imp:
Sinsemilla Jones Reviewed by Sinsemilla Jones on . a theory of mine what would happen if every day or maby evey 7 days u changeed bulbs from a 1000 watt mh to a 1000 wat hps how woudl the plant grow and woudl it be able to adjust to theas changes evey so often Rating: 5