While I tried 1156 Cree LEDs in my reverse lights I went back to incandescent as it was nearly impossible for other drivers to see the lights in daylight from any angle other than directly behind. Backing out of diagonal parking spots became more dangerous than usual.
The 1156 Cree LED lights I used were driven pretty hard and produced a good amount of light, but directly into the clear crenellated lens. I knew it would not use the reflector but thought it would still be adequate. I was wrong.
Now there are T10 based Cree lights which fire not only outward, but are designed to make use of the reflector as well by firing to the sides as well in an attempt to use the reflectors which are designed to use the single point from an incandescent bulb. Some of these lights use SMD led's radially, some others run Cree LEDs.
These bulbs are significantly longer, and can put out incredible amounts of light, overcoming the imperfect mating of light source and reflector. They also might be too long to fit in your vehicle. I knew I could fit such a bulb, but was no longer interested in trying.
Also being longer, they need to be a tighter fit within the receptacle to not rattle their way loose. As someone who has tried a lot of these LED bulbs in T10 receptacles, I must say they vary widely in how tightly they fit, even from the same vendor in the same packet where as the glass base T10 bulbs (192/168/921) always seem to fit tightly.
Just bending out the tangs is not always effective if the base is too narrow.
If you are really intent on trying an LED t10, I'd first measure the length of the bulb which will fit, and try to acquire a bulb which fires radially and outward with multiple LEDs, then hope they fit tightly, and use the reflector, and are not some hideous bluish tint.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dautomotive&field-keywords=T10+cree&rh=n%3A15684181%2Ck%3AT10+cree
