Painting "radiance" in acrylics can be a challenge, given the quick-drying nature of acrylics. I would suggest using an acrylic medium that extends the drying time of the paint, allowing you more time to blend the colors in the soft, subtle way that would suggest the radiance or glow of lights at night.

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Try mixing something like Acrylic Retarder or Acrylic Glazing Liquid with your paint, to make the paint more fluid and also extend the drying time.

To make a smooth transition of color, you'll need to use a glazing technique which I described here. This technique works best for small paintings that can lay flat while the paint dries, because the glazes can get very watery. Depending on the size of your painting, this may or may not be a feasible technique.

If your painting is large enough that you need to keep it on the wall while you paint, use more glazing liquid or retarder and less water, to keep the paint from being too runny. If you apply enough retarder or glazing liquid, the paint should remain somewhat workable on your canvas after you've applied it. You can take advantage of this to paint a few gradations of colors next to each other, and then blend them together to make a smooth transition. After applying the paint to your canvas, use a clean brush to blend two different colors together.