150 watt HPS Light Penetration?

More or less found the answer to my question after some digging. A 150 will probably get you about a solid foot of penetration (from the top of the canopy down), and maybe another few inches of supplementary light.

Of course, if anyone has conflicting info, by all means, share away.

What you stated is a good rule-of-thumb. Of course, the density of canopy will have a huge impact on the penetrating distance. However, even with a thinned out canopy, once the light has to travel more than a foot or so, the fall off due to the inverse square law has a tremendous negative effect.