Interesting, and I could work it out accurately (its been a loong week), but I wonder if Surrey had used 36W Libras rather than 55W, if the proposed switch to LED would have been worthwhile? 36W PL-L being replaced by perhaps 20W LED isn't such a saving. The expected higher cost for power in the future is being used as the main basis/funding for further investment, rather than just the power saved at today's prices.
Also of note is that the price for early evening power, means, dimming (not enabled at that time), is not an option.
I wasn't aware the Surrey had implemented part night in residential areas recently.
I'm not sure what they think is the issue for weather proofing and optical performance for the Arc, when
LED retrofits are already available. A correctly worded contract would pass the risk on to the supplier of the gear tray, not Surrey CC.
No mention is made of further savings from eliminating lamp changes, but the proposed switch over looks like it maybe done as part of that process. Mention is made of "upgrades" to the CMS to cater for LED, but surely this will be just a software change? - LED drivers can still be dimmed by the same system as used for electronic ballasts for discharge lamps.