Need help controlling a relay using a dimming light
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. (a) Relay switches on and off instantly with door switch. (b) Relay held on while the lamp discharges and then drops out.

The combination of C1 and D1 results in smoothing of the lamp voltage as seen by the relay. C1 will probably need to be in the order of 1000 uF depending on coil resistance and required time delay. A rough estimate of the time can be calculated using \$ \tau = RC \$.