If I am storing my bitcoin key on 256 light bulb.
Given a lightbulb weight 10 gram, my key weight is 2kg 560g.
Given that my key store 0.05 bitcoin, it makes around 51 kg by BTC.
But I can influence the weight of a bitcoin by storing more on my key, or using lighter light bulb.
I think it is about time for you to switch to LEDs.