The comparative and the use of lighter

[bananasbana]

I couldn't find much online so I thought I would ask you for help. I'm trying to explain below's topic to ESL students in Japan.

Is lighter an adjective that is an exception to typical logic? It seems that 2/3 lighter than = 3 times lighter than. Because there are different numerical values in front of the adjective, it would make sense that they have different meanings. However, I think that the meanings are the same.

Here are the examples:

•The new model is 2/3 lighter than the old.
o The new model is lighter than the old.

• The new model is 3 times lighter than the old.
o The new model is lighter than the old.

Please help!

[Alan]

To my mind, "2/3 lighter" is meaningless.

You could, however, be "2/3 as light/heavy as".