cone shap is viewing angle, the angle(s) at which the light leaves the lens, currently i have seen 60, 30 and 20 degree angles, between those 3 i like 30degrees.
brightness - leds are commonly judged on their milli - candela output (mcd) currently there are 2,000 mcd - 12,000 mcd leds out there, 5,000 mcd generates a good amount of light for a moonlight setup. an led at around 10,000 mcd is hard to stare at for longer than 15seconds if that helps you vissualize their output.
leds don't generate light in Kelvin temps yet, and eventually though (3-7 yrs from now hopefully) all leds right now (5mm stock) generate less than 1 watt of output power anyway. what they do is provide some light to the tank, that tricks the animals into thinking its night time, and provides us with just enough light to see all the fish and thier nocturnal behaviors.