OK, this is a light rather than a clock - I chose the one that had a USB C charger as it was more suited to what we have indoors already.
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This one says it has an alarm clock function.
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This one is £20 new or has options for Amazon Warehouse for less.
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I can see that the prices have gone up in the last couple of days since I ordered the light, though. All the clocks were all about £5-7 cheaper until the Amazon Sale came along, so I guess it's a seasonal algorithm coming into play.
There are some pretty good deals on Lumies at present if you can stretch to them (always get an LED one, don't bother with the radio options), but I think these are good for deciding if you want to spend the extra; I very rarely wake up before the alarm sounds, but as I'm somebody who, when I actually manage to go to sleep, can sleep through all the tiles on the roof coming off in a storm, car crashes outside the open window and always, always through any alarm known to humanity, I do wake up really easily with these in comparison.
The key is having them so that they are near your face - the light needs to be fairly close, not across the room or behind your head. And I am somebody who struggles to go to sleep in the first place - the first sign of a standard light at night means I ping wide awake for the next six hours; if I'm to go to sleep, I can't have the landing, bathroom or bedroom main light on at all on my way up there. So I know I'm sensitive to light in the first place.