Go with the zip ties over binder clips...cheaper, simple and more reliable.  Cost...$3.99 per 100 at local home improvement store.

Here is a picture of the grow light I used in the construction of my grow boxes.  Cost per light...$8.99 at local home imporvement store.

So my students constructed 13 light boxes for our fast plants.  We went with the design we learned about this summer...2 file crates with the fronts cut out with a light suspended from the top.  I modified the original design to meet fire code, mainly that all electrical cords must inlude a three prong ground and no extension cords are allowed.  I used a shop light, removing the cage that surrounds the bulb, which is a little more expensive but fits code.  Also, instead of using binder clips to join the file crates I used zip ties.  Students kept hitting the binder clips causing them to fall off.  The zip ties are inexpensive and much more reliable. 

One piece of construction advise...I started out using a variety of saws to cut out the front of the file crates to create the necessary opening.  The same week we constructed our light boxes my classes were in our Schoool Forest cutting brush and a student decided to try using a pair of lopper shears to cut out the file crate.  It worked great.  Much easier, cleaner and safer method that using saws.