Touch switch for hanging lamp (touching metal bar): Ideas?
Rather than use DC leakage with a strong CM line AC signal present for touch sensing, this EMI problem may be solved better ways.
It seems your SNR &lt;1 (unless poorly biased, filtered)
Put a shunt R of 1M to earth gnd (across Vbe) and also a &gt;10nF across Vbe with a line f pulse stretcher cap across Vce or across Rc so that  RC&gt;20 ms..This will also suppress ESD if low ESR plastic by 100pF/10nF   ..Otherwise.... plan B.
————
Normally for touch switches a frequency in the x or xx kHz range is sensed by amplitude across the contacts. But here there is only 1 contact (bar) and the other is internal Earth-bonded ground.
So how to detect injected common mode (CM) signal  at some frequency on an “earthed bar”?
Assumptions
The impedance of the bar is unknown but assumed to provide a safe contact in case of a lightning strike or wiring fault. The human’s  impedance for a finger using the HBM (model) is 100 pF + ? R but also the parasitic insulation R (wide range !) and RF characteristic Impedance (377 ohms ) in series with a high C , low R body plasma to a distant earth ground.
I assume you know how to compute impedance for L or C (f).
Thought experiment
Which would work better?

Use an Inductor to bar instead of a wire of impedance X(f) and detect 50V E-field (seen) on 10Meg probe) but now attenuated to xx ? mV line f by ground shunt series L and detect 50,60 Hz low level above e-gnd.
Inject a 100kHz to 500kHz signal into “bar” and suppress with finger capacitance and detect drop in carrier with a BPF and Detector/comparator,
Assume one-shot timer comparator in both to select dim or toggle power.