You can use lights on the sides-4' or less, T5 HO bulbs, Etc. to light the lower reaches of your Terrarium, but there are several caveats to that.

1- Your plants will most likely grow towards those lights due to phototropism.

2- Without a large amount of work, the light will be visible from the front and sides and not be aesthetically pleasing.

3- Duplicating the Circadium pattern of the sun would probably be very complicated and most likely wouldn't net you many if any benefits.

I suppose problem #1 could be dealt with using a timer and many start/stop times on it. That way your plants would receive light, but not all day long and wouldn't receive constant light from the sides. With some effort and engineering, you could probably handle problem #2 as well.

Sam

P.S.- this is JMHO, I am neither an expert, nor someone who has tried maintaining, engineering or designing a lighting system for a very tall terrarium. YMMV.

I think I agree with Sam. It's a good idea for terrariums that are only used for growing orchids and such, but I wouldn't want lights shining in my face when I look into a nice terrarium. And I know for a fact that mimicking the sun's trek across the sky would be pointless. Plants don't actually require this, and don't grow any better with it than they do without. If you have a 4' high terrarium, you should just stick to very low-light plants for the bottom half, or use a metal halide. You can grow ANYTHING with those! And no, I'm not advocating growing pot. =P But you could have a great variety of plants with the full range of light requirements.

Hi
I've tried something like that with growing aquarium plants with mixed results. The benefit didn't warrent the cost or difficulty. lol. IMO the ideal would be dawn dusk simulations from overhead. In otherwords. icreasing the intensity of the lights for two or three hours each day.Afterall this is what happens naturally. Variuos natural colored spotlights could do this with simple timers.
MH would seem the ideal solution except for the drawbacks. They produce great amounts of heat and very intense UV.If your situation is already too warm it requires entire systems to handle it. They are expensive to buy ,operate and maintain.
Of course the great fun of terrariums is to experiment with various systems. lol
Gary