fromEnglish Grammar Today
Efficientandeffectiveare adjectives.
We useefficientto describe something or someone that works in a quick and organised way:
The new online banking system offers a convenient andefficientway to check your account.
[extract from a reference for someone applying for a job]
I have always known James to be highly competent andefficientin all aspects of his job.
We useeffectiveto describe something that gives you the results you want:
Taking this tablet is a veryeffectivecure for travel sickness.
In this light, the camera is moreeffectiveif you use the flash.