150w standard bulb = ~120w halogen, allegedly = approx 1400lumens.
colours:
the ice blue white (6500K colour temp) is the most efficient (for LED and fluorescent) so will give you brightest illumination per watt, but they come in a range from 2700K very warm white (compact fluorescent / standard incandesent). most LED warm whites I've seen are 3000K ish. there's also a 'natural white' which is in the middle-ish 3500 - 4500K.
LED do come on at full brightness without having to warm up so I'd look for something LED, warm white, and 1400ish lumens - if they say "equivalent to..." without giving a lumens output, I'd avoid them. You may struggle to find a bayonet LED equivalent to a single 150w so you might need to use say 3*450lumens - alternatively look at the floodlight fittings.
standard B22 bayonet 470lumens (warm white):
http://www.ledhut.co.uk/led-bulbs/b22-led-bulbs/7-watt-b22-high-output-standard-shape-led-bulb.htmlor 850lumens (warm white) flood:
http://www.ledhut.co.uk/led-flood-security-lights/new-10-watt-led-floodlight.htmlAlternatively you could consider good old-fashioned linear fluorescent which can still be bought with old type switch-start ballasts - although they have a flickery start and do have to warm up, they tend to come on brighter than the electronic-ballast fluorescents.