Is directed lighting possible?

I'm working on lighting for a performing space, and wonder if it's possible to have directed lighting, as in light that points from Source A to Area B. I'm not talking about lighting such as you see in clubs, with faux beams that simulate a projection of light. I'm talking about being able to narrow the radius of a light source.

As far as I can tell, when I create a prim, and turn on its "light", the light radiates out equally in all directions from the prim. What I'm hoping for is a way to, for example, block the light emissions from 5 of the 6 sides of a cube so the light is only beaming out in one direction.

Is this possible or just a pipe dream?

Thanx

its a dream at this moment

It is not possible in SL to do real directed lighting. Open GL doesn't support it.

You can get something close to a beam of light by using a phantom prim in the shape of the light beam, mostly transparent and set to fullbright and as a local light source. Or better yet, with several small local light sources embedded in it, that are fairly weak, spaced along the beam.

Nice explanation Ceera, could you expand a little about the ‘small local light sources’

I'd love to see a more detailed description, Ceera

in theory the little lights are a good idea, but open gl only renders the 6 nearest light sources to you, which would render the effect pretty much dead

The last poster was right that the usefulness of this trick is limited by how many local light sources Open GL can render, but in some cases this is handy...

Any prim that emits local light does so from its geometric center. Not it's surfaces, not it's whole length, but a pinpoint at the center of the object. And it does not matter if you can see it! The object can be 100% alpha textured and can still emit local light! Depending on your video card, you can percieve local light from the nearest 4 to 6 sources.

Let's say you wanted to do one beam of light into a darkened dance floor. The beam will remain fixed in place, and will be 6 M long from the "light source" to the dance floor.

Make the "beam" as a fullbright phantom prim, a tapered cone, mostly transparent.

Place a 100% alpha textured sphere, 0.01M in diameter, about 2 M from the end of the beam of light, and set it to emit local light. Make it phantom and link it to the light beam prim.

The effect of this wil be a pool of local light where the beam hits the dance floor. And it still is only one local light source. You could have 4 to 6 of these in an area, and all would be percieved as casting light.

But what if you also want the beam to "illuminate" a balcony that it is passing by?

Add one more 0.01 M, 100% alpha sphere, make it a phantom local light source, and position it in the path of the beam prim, linking it to the beam. Make this one a weaker light source, unless part of the beam is actually striking the balcony.

Two point sources, so only 2 to 3 of these in one area will render light.

And by the way, no, light doesn't cast shadows, either. The shadows at the feet of your avatar are a fake that only works with avatars, not objects.

Two point sources of light, but it looks like a directed beam.

Most solutions involve a workaround to get over SL's lack of ray casting features.
If you're trying to do a stage setup, such as a spotlight directed on a stand up comedian, you can try using sets of textures that change when you click something or issue a command on the prims.

I've experimented this for lights in a house, where there are two sets of prims for the walls and ceiling. One lit using photoshop, and another just normal. So when you turn the light on, the normal prims turn invisible, and shows the ones underneath, thus simulating the light being turned on effect.

I use this instead of a texture switch because its more instantaneous, without the loading time, since they are already loaded anyway, just hidden.

A big big thankyou Ceera, brilliant and works very well indeed.

Good trick. Another one which I've used is having both textures in one (side by side) and changing the texture offset to switch, or rezzing the "other" texture on a hidden face (inside of a sphere for example) which will still load it.