Archive for December, 2009

Not An Introduction to Second Life Prim Lights

Tuesday, December 1st, 2009

This is dedicated to those knowledgeable and helpful folk over on the SL Universe forums, without whom this post might never have been written.

This is not the post I was going to write.

I was going to give an introduction to using Second Life prim lights. Because I needed some illustrative snapshots, I created a simple prim, activated the light feature, and started taking pictures.

At which point I realised that after five years in Second Life there are still things that I don’t know, one of them being that lights don’t quite work how I expected.

As an example, here’s a cube which has been turned into a light-source. You can see it lighting up the floor, as expected:

Well…maybe not quite as expected. Why does the light have such a peculiarly elongated and patterned appearance?

What’s happening is that the light is revealing some of the underlying structure in the Second Life world. Turning on wireframe (this is in the Advanced menu, if you want to try it yourself) gives an indication of what is going on. I won’t post a picture, because a static picture of the wireframe view is just a confusing mass of lines. If you try it yourself, though, you will notice that the lines and intersections (technically known as vertices) match the pattern of the light. When a light shines on a prim, the appearance is changed at the nearest vertex.

Let’s move the cube so that it is ‘between’ vertices:

The light fades. It doesn’t vanish altogether, but it is certainly less visible.

If the cube is moved again, over the next vertex, the full light returns:

If the light follows the vertices, what happens if the prim that the light is shining on is resized? Given what we’ve just seen, it’s perhaps unsurprising that resizing the prim will change the appearance of the light:

This has the odd result that resizing the light prim has no effect on the light that it casts, whereas resizing the prim that the light falls on does have an effect!

So, when you are trying to set up lights in Second Life, you have more to think about than you might have imagined. The position of the lights in relation to the prims that they are illuminating, and the size and shape of the prims that the light falls on, all have an impact on the final appearance of the lights.

In the next article in this series I will go back and write the post I originally intended, and give more of a basic introduction to lights.