...but I don't know how to convert 'Luminance 16CD' to lumens, and it's battery powered rather than mains.
I'm fully with you, and have looked it up in Wikipedia without lasting effect in my memory. So, as a morning exercise, I revisited those pages.
Light -- as perceived by humans -- is a subjective matter. The eyes don't see all wavelengths, and those that they do see, are not all seen with equal sensitivity. Take an easy example, an IR emitting LED. Although one could measure the emitted power ("radiant flux") using some physical measurement tool, the eye would still not see anything. If we take two LEDs, one red and one green, and the tool tells us the power is equal for both, our eyes will tell us the green one appears brighter.
Thus, the standardised "luminosity function" tells us how much more power the red LED would need to emit before the eye sees green and red LEDs as equally bright.
And if we now had measured ALL light that was emitted from the LED (that is, in all directions), and normalised it with the luminosity function, then this quantity would be expressed in units of "lumen, lm".
But how useful is that? In an application like a worklamp, we want to make sure the lamp lights up the work piece. So, we want a measure of how much light is radiated into a certain direction. This is where the "luminous intensity" measured in units of "candela, cd" comes in: this is as before the emitted power (in Watts), weighted with the sensitivity of the eye, but measured per solid angle instead of as a sum of all directions. So, candela equals lumen per steradian.
Apparently, the EU tries to help us out of this confusing question:
"On 1 September 2010, European Union legislation came into force mandating that lighting equipment must be labelled primarily in terms of lumens, instead of watts of electricity consumed.[5] "The 127-LED worklight you linked to is spec'ed with "Luminance 16CD". Erm, "luminance" is a measure for how much light a given surface emits, for example a computer monitor. Measured in cd/m². But let's assume they meant "luminous intensity". If the worklight emitted a beam angle to illuminate say 120°, than that equals a solid angle of pi steradian. To calculate the approximate equivalent "lumen" value, we just multiply the candela rating with this assumed illumination angle: 16 cd*pi sr equals approx. 50 lumen. 50 lm out of 127LEDs?
In summary: I'd stay well clear of that worklight, unless the seller / manufacture provides more meaningful information (or at least adhere to the mentioned EU directive).
Klaus
