How can I achieve very bright light?
Maximising brightness:

Brightness is a function of amount of light and area illuminated.  


More light = more brightness. 
Less area = more brightness.


So 

For more light obtain as many lumens as you can afford.

For less illuminated area use LEDs with low "radiation angle" or "cone angle". 

Lenses: 

If that is not bright enough you can use a lens or reflector.
 Many companies provide lenses for LEDs.
 Deal Extreme have a range here

Effect of colour:  Note also that brightness is related to eye response to colour - yukky yellow green is about the best colour for optimum eye perceived brightness - but if you want a specific colour this is not much help in optimising brightness. 



Related: Mind plasticity add on for the ever young:

Lime Green is close - Lime Green Fire Engine from here - BUT more recent studies suggest that familiarity is more important than visibility for emergency vehicles.