Yes, it's another A2 poster "book". You probably can't read the text running across the top and bottom at this size, so here it is:
As well as its visual and metaphorical sense of "lit from the side, or a tangential insight" a sidelight, in British usage, is a window located to the side of something, typically a door. As opposed to a fanlight, which goes above the door. We live in a typical 1930s semi-detached house, with an elaborate part-glazed front door and sidelights made up / of leaded panes of various types of pebbled glass, in a vaguely Art Deco sort of pattern. As our house faces south-east the morning sun shines directly through this glass frontage, so it has become a very familiar set of shapes over the years: on a bright morning, the lattice of lead cames is practically burned onto your retina as you come downstairs.
Surprising, isn't it, that you can get all that into just two lines of 11 point type? An A2 sheet is bigger than one thinks. Did you notice that word "cames", by the way? It looks like a typo, but isn't. Definition: "a grooved strip of lead used to join pieces of glass in a stained-glass window or a leaded light". I think I must have first (mis)heard it way back in the 1970s, when my university friend Leo first got into making stained glass in a big way. I like it when there is a precise word for something which would otherwise be hard to describe in fewer than twenty words, although its usefulness is obviously diminished when most people have never heard it, and don't know what it means, so you end up using those twenty words, anyway...
I have always enjoyed these venerable specialist terms from arts and crafts. In fact, it reminds me of one of the very earliest posts in this blog, written after I had encountered the stonemason's term "batting", and discovered it was missing from the OED. I had come across it when doing a little research on the Mottisfont terms / herms, as in the inventory of the Abbey made by the Historic Monuments Commission they are described like this:
4 thermae, C18 stone, male & female heads standing in front of box hedge set on large radius, set 10m apart and 2m high. On low moulded plinth, foliage to front, batted, tooled finish to sides, 2 male & 2 female busts.
Batted? Huh?
I did let the OED people know about their lapse at the time, and it occurred to me, writing this twelve years later, that I never did check whether they got around to amending the entry for "bat". So I just did, and they haven't. Never mind, we know what it means. Although we'll still be obliged to explain: you know, when fancy stonework is faced with decorative parallel grooves, carefully done with a chisel... What do you mean, you don't know what "faced" means? Oh, look it up... That one's definitely in the OED.