This tutorial is made for TF2, but applies to other games too!
If you haven't already, be sure to first off check my other tutorial, explaining the basics of creating a map!
Now, you've created your chamber, but the light does not look right yet! It's way to bright! Also, it's a 'magical' light, without a proper 'source' to shine from.
Start Source SDK and open your map again. Click the lightbulb ('entity tool') on the left bar. Now, type on the right bar: 'prop_static'.
We'll add a proper light source now. Click somewhere in the map. This red box should appear:
Next thing you want to do is press ALT+ENTER. Now, the properties of the red box (prop_static) should open.
Click on 'world model' and click browse. The model browser should now open. Type in the filter 'light' and scroll down till you find a good light source. I'll take the 'light fluorescent_farm' It's about on 1/4 of the list.
Press 'ok', then press apply and exit the 'object properties' menu! Now, you've imported the light model into your map! Good work.
Pro, but quite obvious tip: Don't put any HL2 models in your TF2 map.
Next thing you want to do is hang this light from the ceiling. I'd advice you to higher up the ceiling and walls a little, because otherwise, people will walk into your light.
You can drag walls by clicking on them in the 3D view, then dragging them via the small boxes on the edges in the 2D view!
Done that? Now drag the prop to the ceiling, using the side and front views.
If you still have a light in the room from the other tutorial, you can skip the next step.
Make a new entity via the lightbulb on the left, make a 'light'. Just type that in the bar on the right: 'light'. Click somewhere. There's your light.
Don't skip anymore:
Now, the next step is dragging your light about right underneath, in the middle of your prop. Place it as you see it on the screenshot:
Protip: You can change the grid by pressing [ and ] on your keyboard. Press it once so you can put the light in the middle of your prop!
Right, now it's time for a test run! Press F9, you might have to save your map (don't change the save location!) and press 'ok'! Now wait for TF2 to start, and take a look!
It's looking better, but it's still way to bright. Go back to Hammer, select the light entity and press ALT+ENTER again. Now, click on the 'brightness' tab. The first 3 numbers represent the Red Blue Green values, you can leave those for now. The last number, the '200' represents how bright it is. Try changing the number to 50. Press apply, close the screen and press F9 again. Let's see:
Better huh? And that's all there is to it! Never forget to put lights in your map, otherwise they'll just look silly.
If you're making a themed map or something, try experimenting with the brightness of the light. (The colour values, that is!) Just go back to the light properties, go to the 'brightness' tab, and press 'pick colour'. Pick out a colour and compile your map!
Look at my WiP map to see some examples of blue tinted lights:
If you have any questions, place a comment, I'll [try to] answer them all!