Warning dont order from these people

My 1141 stock trailer bulbs are 18.4 watts and from what I've read, suppose to be approximately 260 lumen. My 1141 TH bulbs put out much much more light than these 24-5050 panels. The 24-5050 should put out over 360 lumen. Either the led ratings are way off, or all led smd 24-5050 panels are not created equally at all, huge difference.

The LED ratings you used to transpose to actual use are just that, ratings. They are done under lab conditions where everything is controlled and different methods are used to get to that level.
I would doubt that an 1141 disperses 260 LM, more like 100-120LM.

Your last sentence in this quote is the crux, not all LED illuminators are equal. Even similar architecture and LED size from the same or different vendors may differ in output. For my use, I found that the SMD48-1210 are equivalent to the bulbs they replaced. My float voltages can range from 13.2->14.15 so supply voltage has never been an issue. I bought my panels from a variety of E Bay vendors, using small sample quantities until I received panels that I deemed acceptable. I do have one 12-5050 LED panel in 5000K temp that I find inadequate for it's application. It will be relegated to reading light or accessory location.