(Anecdotal, not scientific) From what I see of cyclists riding during the bright sunlight here in the desert, a flashing light shows up a lot sooner than a steady light. For daytime use, a bright, concentrated light is going to be seen sooner than one that is spread across a bigger area. Of course, the brighter the light, the more likely it is to be seen but run time or battery life is indirectly proportional to the brightness for similar mAh batteries. During the day, 50 lumens is not much for a tail light. Prices have fallen recently on the newer USB rechargeable COB tail lights. I just got one in the mail today that cost me less than $5 including shipping. Raypal RPL-2266 COB LED Bicycle Bike Cycling Front Rear Tail Light USB Rechargeable 6 Modes Lamp | eBay Took 13 days to arrive in the mail from China.

At least for tail lights at night, the bigger the lit area, the better it can be seen. I made a set of DIY light sticks for my recumbent trike that are 11" long with 87 colored LEDs spiral wound around a 3/4" plastic tube. It can be seen 360 degrees and a long way off. I wanted to be sure nobody could say they didn't see me coming. Runs on a 12V lithium polymer battery with a run time of more than 12 hours. Cost for a pair with battery and charger was about $25.