LED security light faint glow

This issue is not unusual for LED lamps particularly when installed in older wiring installations. There can be multiple possible reasons for the glowing when the lamp has been switched off and whilst in my experience the issue does not create any detrimental impact on the lamp or on its life cycle it is more a nuisance and can be disconcerting. From the description you have provided I am going to assume that there is just the one fitting attached to the switch and the switch is not a dimmer or smart switch. Additionally, I am also going to assume the cabling, specifically the insulation resistance is good. If this is the case I believe the possible cause is capacitance being created in the switch wiring. By the way before I continue, I am not going to suggest that a re-wire should be carried out. In electrical theory, a voltage induced in a cable creates an electrical field around the cable which in most circumstances is ‘soaked’ or ‘drained’ through adjacent neutral and circuit protective conductor (earth wire) in the same cable. However, in older wiring systems the installation methodology may not be conducive to the pre-said and the electric field is not drained. Consequently, the permanent live wire in the switch which will have an electric field around it will migrate into the switched live in the switch which is connected to the lamp. So, when you switch off the switch a capacitor is basically created across the two cables in the switch and effectively a small voltage is induced in the switch wire. A small current is present and travels across the electric field which conducts through the LED lamp and through the neutral creating a circuit and causing a low glow in the LED lamp. To possibly resolve the issue would be to connect a resistor across the cables which would be counter intuitive to LED energy saving benefit. Probably the more appropriate resolve would be to connect a correctly sized neon across the circuit behind the switch which should act as a drain. I hope this helps and possibly supports a resolution to the problem?

What he said. Great answer. Neon switched spur instead of switch