Quick comparison of 2 very popular tail lights. Solid and proven Blackburn Mars 4.0 with 1 Watt LED vs. CygoLite HotShot with 2 Watt LED ( premium version with up to 500 hrs of run time, and 5 customizable modes ). Both are considered as a "day time" tail lights. ($20-$30 as of today)

Bicycle Tail Lights Cygolite HotShot 2 Watt vs. Blackburn Mars 4.0 1 Watt LED Comparison - YouTube