And that can only happen if the light is brighter. Again, this is another misconceived parameter "water penetration". The only reason a given light penetrates freshwater deeper than some other light is because it's brighter. Not because of any voodoo or special quality of the bulb technology.
In natural salt water systems the story is radically different. Lower frequencies, such as red, yellow and green get absorbed at shallower depths, so that only the highest frequency light can penetrate to the lower depths. This means blue and indigo are the last to be absorbed, and that's why the ocean appears blue. In a marine tank though, you'd need at least a 15 foot depth before you'll start to see falloff of the lowest energy (Red). Again, this assumes that the light source mimics the sun's spectral energy profile. Since no bulb can even dream of mimicking the sun's profile the penetration issues are more complicated due simply to missing or subdued frequencies.
By about 50 feet every color produced by the sun except blue is absorbed. By about 330 feet the last of the sun's blue is absorbed by the ocean.
In fresh water (as well as in salt water) there are other factors, such as angle of the sun, latitude, refraction, reflection, planktonic activity and turbidity that limit light penetration in natural systems. In our case, at our very shallow depths, the only factor limiting PAR penetration is strictly the bulb output. Either it's bright or it's dim, and the brighter it is the deeper it penetrates.
Therefore, if the T6 bulb appears brighter to you then that brightness will translate to a deeper penetration towards the substrate.
Cheers,