Unless it's really necessary, adding a dimmer is another part that can go wrong. In this case, more than likely not. The T8 is not powerful enough to cause damages at the recommended operating distance. In fact it will not damage plants even at 10", though not recommended due to coverage limitation. Even with our atmosphere, clouds, ozone layer, etc., uv level from sunlight is still much higher than most supplemental uv enrichment so plants can usually handle anything we can reasonable throw at them. Two hours after light on for eight hours is good from the time pistils appear is usually a good rule of thumb for uv. Blue spectrum at sufficient level is also known to increase resin production, because like uv, it's also a high-intensity short wavelength, just not as intense. It goes from uv, violet, blue, green, yellow, orange, red, far-red and the into infra-red on the spectrum chart.