At 51:00 the camera moves and you can clearly see a modern Electric lamp on top of a post with the light taken out as Electric lamps were not around at this time.
The lamp on the top of the stone gatepost at Culverton Smith's house is clearly a modern electric lamp with the bulb removed from the light bulb socket. It is seen twice, when Mrs Savage parks her carriage in his drive and again when Holmes arrives outside the gates.