Note that there is a minimal amount of Ultraviolet B (UVB) in comparison to sunlight, when a lamp is new, as in this example.  Full spectrum lamps lose 10% of their ultraviolet output within the first 500 hours of operation.  It is therefore unlikely that sufficient levels of UVB remain after this time to provide Vitamin D synthesis.  60% or more of Vitamin D synthesis occurs in the D-UV segment of the UVB band.  The dip in the yellow zone of the incandescents is due to the filtering capability of the element Neodymium.  So called full spectrum incandescents use this to remove as much of the yellow light as possible, making the lamp appear to give off a whiter light.  It is obvious from the chart that these devices do not even come close to being full spectrum, or duplicating sunlight.

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NOTE:     Almost general illumination full spectrum lamps have a UV/UVA cutoff of approximately 350 nm, equivalent to the UVA output of standard incandescent devices.  These wavelengths are not within the Vitamin D synthesis range.