here are some tips for you ...

the light is all wrong .... your running around 3400 K ..... its totally wrong for veg .... you need to run around 6500 k for veg .... save that red light for when you want them to bloom like crazy .... (LOL)

In addition ..... cukes are vines ... and your gonna need ALOT more light then that ...

there is a special way that you have to prune indoor cukes .... inorder to get them to produce fruit ... do some research on that ... in addition you will need something for them to climb on ... trellis or something like that ...

that yellow on the leaves is definitely a nutrient deficiency ... if you want to make it longer invest in a nice balanced nute like botanicare pro grow/bloom/liq karma ... they have a starter pack for like $15 bucks .... and you will really see some roots then! ...

good luck ..... cukes are tough to grow indoors....