That is mainly because solar LED lights use direct current, and the working voltage is generally 12V-33V, with constant voltage and adjustable current.
There are many types of chip packages for LED chips, and the wattage of a single chip is also divided into high power and low power, with single 0.3W, 0.5W, 0.7W, 1W and other wattages. So there will be a difference.
If the LED uses a single 1W chip and the number is 30, then the full power of this lamp is 30W, so a solar LED lamp cannot accurately determine the full power of the lamp head simply by the number of chips.