Not enough light makes them grow tall and fall over (it's sometimes called 'leggy'), much like your photo shows. Excessive heat (above 80 degrees) will cause it too, but only for lettuce and cole crops, as far as I know. For everything else, it seems to be not enough blue spectrum light that makes them grow tall and weak.

Iliketoast, thanks. I think that is the case (that it doesn't get enough sunlight). I didn't know that legginess would happen/apply to grown plants. I thought it happened with seedlings only.

But does it affect the plant itself? Aside from the weird look, it still tastes good to me, but I don't have others to compare.

When it comes to lettuce no it doesnt affect the plant - other then it growing slower than if it had optimal light. If you were growing cukes or tomatoes it would affect the plant because you likely wouldnt get fruit (insufficient light)...

Plants in the garden often are light starved too. Think of A huge tomato plant growing on the south side of some smaller plants...those smaller plants are fighting for light too.

Here is a link that might be useful: The Prudent Gardener

What is your light setup and how far from the plants?

What is the room temp?

Flouros are good with lettuce as you can place it close to the plants without overheating. Flood them with light at least 12/12, or 14/10 and watch the results. They should grow very dense.

Maybe add some mylar to the sides to get additional photon collection?

Here is a link that might be useful: My Hydroponic Journal and Videos