Both battens draw the same amount of power (45W), but the first one gives out more light than the second.
The first batten is able to deliver more lumens (6,000) because the LED chips inside are more efficient.
Technically, a lumen is an ‘SI unit’ like metres, Celsius, kilograms, and so on. Whereas a metre is a measure of distance, a lumen is a measure of ‘luminous flux’.
When you see either ‘luminous flux’ or ‘lumens’ on an LED data-sheet, you need to check whether these terms refer to the LED chip or the overall fitting.
For example, the LED chips in a light may have a luminous flux of 4,300 lumens, but the overall fitting might have a luminous flux of only 3,700 lumens. It is important to focus on the 3,700 lumens figure, as that is the actual amount of light coming out of the fitting.
Where are the missing 600 lumens? Most of these are lost as the light travels through the diffuser that sits between the LED chips and the observer.
Lumens are not to be confused with Lux.