If you already use white light, you only need to fill in the missing wavelength in the lower blue and upper red area, if any ..!
I've added ~6% 425nm(SemiLED has good ones) and 10% 660nm(Osram, Cree, Philips are good) to my 3500°k Cree COB's.
While the deepred seems to have no visible effects, except that it increases the overall output, the purple blue light has produced clearly visible changes. Plants keep shorter and more bushy/dense, leaves stay a bit smaller but gets a darker green, also they looks and stays healthier. They barely lost a leaf until the end. Buds are more dense, terpenes and resin content seems also better because of the lower blue wavelength.
That's what heliospectra says about these wavelength:
Violet (380 nm to 445 nm)
-----------------------------------------------
Studies have shown that when a plant receives visible violet light, the color, taste and aroma of the plant are increased.
In addition, the antioxidants of the plant are able to perform their functions more efficiently, which prevents the cells from being damaged in the plant.
This is broadly consistent with my experience.
Wideband reds are nice as well as monochromatic reds but today I would recommend to use a good CRI90 LED to get more deep- and far-red into your growroom.
BTW,
UVB reptile tubes are even more useful than purple LEDs. In addition to UV-A and B wavelengths, they also provide a lot of blue light in the 410 and 435nm range, but if properly used, they significantly increase the active ingredient content. We're talking here about 15-30% more thc.