Prior to going on holiday over two weeks ago i decided i would connect a stand alone type pir detector (1Kw handling) to switch my 3 exterior lights [on] at a preset darkness.

Only when i looked at the instructions on the box/carton it said for incandescent lamps only...The lamps insitu are the D type Fluorescent 16W per lamp, what i would like to know is why i cannot use this stand alone pir to switch Fluorescent types, my immediate thoughts were the momentary lapse in start up voltage from these Fluorescent lamps are the reason!

NB: Just left the 3 lights on permanent whilst absent on Holiday.

I'm not sure. It may be that the ballast for your flourescent lamps have a large "inrush" current at startup. If that's not the case, then you might be OK to connect your detector. But check w/someone more knowledgable than I before you do that. Otherwise, you mihgt just try a simple timer.

Usually they just switch using a relay, electronic ballast low-energy 'bulbs' should be fine.

I suspect it's old flourescent fittings they are concerned about, the back EMF from the ballast choke makes the contacts arc across.

Because some florescent ballasts need the sin wave to be fairly pure for their electronics package, anything coming out of a Triac is not so smooth.

TRIAC controllers in these devices typically trigger near zero crossing. CFLs (and fluorescent fixtures) draw almost no current at zero cross because the voltage is too low to make the lamp conduct.

So the TRIAC gate is triggered at zero cross, but turns off (or sometimes never turns on) due to lack of holding current. Later in each cycle of mains voltage, the lamp is ready to accept current. But the TRIAC gate is no longer being driven.

It gets worse. Sometimes the TRIAC triggers and holds. This is on random cycles, and is really bad for the lamp (and controller).

(it will work fine with CFLs too if you don't mind the crappy light-up time)

Maybe I went into too much detail and nobody finished reading.

Before posting my reply I actually hooked a couple different CFLs to a TRIAC-based PIR. I looked at the waveforms. I have a Leviton PR180 which will not drive a variety of standard CFLs.

The typical cheap CFL presents a load which a TRIAC cannot drive.