how to switch 12v500ma with 5v signal

i have some leds with a total of 400mA@12V. and an arduino with 5V output to switch it. which transistor is appropriate? a bc557 get too hot imho.
edit: i could use 4x bc557 as it's 4x 85mA to be precise. but i'd like to use 1 fet only.

I'd suggest using a solid state relay (ssr) instead.

The cost will be marginally higher (and to a lesser degree, more space taken up) - but you'll have tons of overhead in terms of switching current capacity. Since it all starts with 400ma and next thing you know...

It also provides some isolation to the Arduino pins should things go awry.

I'm using three small omron ssrs to switch LEDs/etc from a beaglebone black this way.

none if the ssr i can buy locally fits size wise. so maybe anyone has got a suggestion for a regular easy to source fet?

use a 5volt gate power mosfet, can switch amps!