Light manufacturers use a variety of terms to market their lights and globes. In the following article I have explained the most common measurements or marketing terms you will come across when purchasing driving or work lights.
The information provided here is to the best of my knowledge and experience and may contain my personal opinion.

Candlepower – Measurement in Candela of the brightest part of the beam produced.
Lumen – Measurement of total amount of visible light produced by the light source.

(The difference between Candlepower and Lumen can be explained by covering half a light bulb. Candlepower will remain unchanged as if you look at the uncovered side it is just as bright. Lumens will be halved as only half the amount of light is now visibly being produced by the globe)

Lux – Measurement of the amount of light per square metre of surface area.
Watts – Total power consumed to produce the light. The type of light source determines how actual light is produced. Incandescent or halogen globes commonly produce less than 5% light from actual power used. The rest is produced as heat. (5 watts of light energy from a 100 watt globe)

Lumen/Watts is a measurement that LED manufacturers like to use and it is simply telling you how many lumens of light you get for every watt of power consumed.

Plus value – Many halogen headlight globes are using better glass and gas technologies to improve light output. If the packaging says Plus 50 or +50 they claim it to be 50% brighter than their standard globe.

Colour Temperature – This is a guide to the whiteness of the light rather than its intensity and is expressed in degrees on the Kelvin scale. If two equally intense light sources differ in colour temperature, the eye will perceive the whiter source (higher colour temp.) to be brighter.

When comparing lights for automotive application it is best to use Lumens as a guide to light produced and Watts as a guide to power consumption producing those Lumens.
Lux is important to determine brightness within different areas of the beam spread and is usually provided by the manufacturer as a diagram of beam shape with different colours for different Lux values.

Candlepower is not as useful in general, but could be used when comparing pencil or spot beams.

A good example would be to compare a laser pointer to a torch. The laser pointer will have a much higher Candlepower measurement as all the light energy is focussed into one small point, but it would be useless to use as a torch!

Choosing Lights Part 1 – Understanding the terminology