That is PVC pipe in my picture. A 16" long section of Schedule 40 PVC irrigation pipe weighs 100 grams (~ 3.5 oz) and you only need about 2". The 2" steel corner bracket weighs 16 grams (0.57 ounce). The advantage of using PVC is that it is much easier to cut and drill holes in it. You can use almost any hard plastic tube that is 1/2 to about 5/8" diameter.

I no longer use lights that require disposable batteries now that USB rechargeable lights are available. The 100 lumen Raypal 2266 shown has a 500 mAh lithium polymer battery and the Lezyne clone has a 650 mAh lithium polymer battery. Both lights cost me less than $5 and will run for at least 6 hours in flashing mode.