Yes, we/you really need to know that - as SUNRAY has said, winston's 3W per PIR may be pessimistic in terms of modern units. However, I nevertheless suspect that 19 of them would very probably consume more electricity than they saved, even if appreciably less than 3W each.
Kind Regards, John
manufacturer has replied to my query, says PIR consumption is 0.5W so that’s (scratches head) 1 unit in 2,000 hours = about 4.5 units per year which will be about 80p per light per year on our current tariff. I think I can live with that!