I wonder if adding reflective ("mirror") tape to the base of the housing (the part attached to the bike) could help. The stock setup is matte silver. I wonder if reflecting more of that light would increase apparent intensity to anyone following the bike.

@Rallyfan,

My guess would be 'no' because the lenses are designed very specifically for the light source which is why it works best with an incandescent bulb. A shiny silver surface would make the light more 'pointy' sharper if you will. Whereas if the surface has some texture, it give off a more diffused reflection and the lens will be designed exactly for that type of diffussion.

This is why photographers don't use mirrors to reflect light onto an object they use a white card, or if they do use a shiny surface then it will be very bubbly and textured.

Hm... So maybe that's why the base surface is matte grey. I might experiment with red reflecting strip tape in there; it's got facets and should angle reflected light. Anything to maximize visibility.

Just figured I'd post some information here (for search reasons) about my experience yesterday with the swap to LED bulbs.

EDIT: The bulbs I am now running in my red GSF style tail light lens are these here in cool white:
https://www.superbrightleds.com/moreinfo/tail-brake-turn/1157-can-bus-led-bulb-dual-function-26-smd-led-tower-bay15d-retrofit-car/1166/2985/
They are brighter than the stock bulbs and work great. The red doesn't look washed out and the white shines down onto the license plate.

I also bought these for my gauges which turned out to be a bit too dark for my liking... I bought a couple different colors to play with and blue one for the speedo wasn't bright enough to light up the trip counter.
https://www.superbrightleds.com/moreinfo/miniature-wedge-base/194-led-bulb-1-led-miniature-wedge-retrofit-car/197/854/

BUT I'm glad I bought them because they are a perfect fit for in the Neutral, High Beam and Oil indicators. The E bikes must use the same socket as for the gauges because based on two other recent threads, the F bikes use the really small 74 bulb for the indicators.

That being said, these are the 74's I thought I needed but they were impossibly small and would not work (again, for my E bike... but others have said they work for the F's).
https://www.superbrightleds.com/moreinfo/miniature-wedge-base/74-led-bulb-1-led-miniature-wedge-retrofit-car/226/1060/

One final note I'll add is that based on what I experimented with, a white bulb behind the colored lenses looked just as nice as a colored bulb behind the colored lens. The white didn't wash out the color or look to bright IMO.

Don't know if they fit in a GS taillight housing, but I have these angel eyes on my GR650:

https://www.superbrightleds.com/moreinfo/led-headlight-accent-lights/led-halo-angel-eye-headlight-accent-lights/49/

Along with some of their other 1157 led bulbs (that I can't find right now....). The angel eye rings are only wired to the brake light, so the running light is fairly dim. Once the brake lights come on, it's a fairly impressive amount of light.

@Rallyfan,

I have received the GE nighthawk and they are pretty well identical in output to the original Stanley 32/3cp that I presume the bike came with.

However I eventually took delivery of the Honda OEM bulb which is a Stanley 43/3cp and I can confirm that they are much  brighter than the nighthawks, which is what I would expect as they are rated higher yet are still 21/5W 12V.

http://www.ebay.com.au/itm/272047902846

Thanks for the info I appreciate it!