I think it is a pity when gardens close for the night. At once, they are preserved from the night terror of vandalism (it is amazing how many plant labels people take- this is one of the most surprising things I learned when I worked for a public garden) and also deprive the appreciative night-going onlooker. So many flowers have different night-colours, and the whole set of available aesthetic elements turns sideways when there is much less light by which to see a garden.
Lucky, Bellevue Botanic is open "Dawn till Dusk," the exact times of which I find open for debate.
And after all that, I must say that nighttime photography is beyond my skills, so here are photos in the evening hours, at least. In which I note, that low-angle lighting ( aka "God lighting." -John Greenlee, Author of 'The American Meadow Garden') is ideal lighting in which to enjoy plants.
My overall feeling about Bellevue is a nice exhibition and space of things that grow well in the Seattle area. The Rockery leaves something to be desired as a plant collection, but the rocks are arranged to make for a great space one day. The Asian end of the garden is particularly well composed, perhaps my favourite.
The Alpine Rock Garden at least looks good from a distance (I should like to think the same is true of myself.):
I don't know what this tree is, but I want it: (This one's for you, Debra, you lover of peely-skins)
Alright, here is at least one picture that captures the majesty of even a soccer field at night. (Despite being a monoculture of turfgrass- enjoy the lighting!)