Growing room and the plants response

We have been looking at the costs of the growing room (seen here with lights off), trying to decide on the value of running it against electricity costs. We have onions in there now lighting 20hrs per day maintaining a maximum temperature of 18.5c to a minimum of 12c.

Three weeks ago we sowed Ailsa Craig onions and put three trays in the tunnel and the same under the lights. Below you can see the comparison the trays n the left are from the growing room those to the right are from the tunnel.
You can see that not only are the growing room plants bigger but they are darker green and generally healthier looking.
We will see over the coming season which will produce a better crop but so far the groing room plants look well in advance and will probably repay the cost of electricity.