LED is so expensive, why is it said that the high cost effective?

Yeah, LED is expensive, but for the cost-effectiveness is concerned, this is just one of the considerations. Similarly, for now not expensive LED products, you have to know, this is just one of the considerations!!

if we consider the overall cost-effectiveness, then, from a full life cycle perspective, that is to have the whole life cycle the concept of cost, not just consider the initial cost. LED is more energy efficient than conventional light sources, it is estimated that if all are replaced by LED light source, you can save 30% of energy, and lighting, accounting for almost 20% of human energy consumption. For the older and more power light sources such as incandescent, by simply replacing the LED bulbs, we can achieve 70% energy savings. LED's last longer, so replacement costs and lower maintenance costs during the whole life.