It was easy with 'old' incandescent lighting (well, actually, it wasn't but we got used to it! )
We all knew (or had a pretty good idea) what a 40W, 60W or 100W light meant - and what we might look to use in a particular lighting situation.
Then along came Compact Fluorescent Lighting (CFL) which used a lot less 'power'. But it was still (almost) straight forward, as the CFL bulbs were almost always labeled with incandescent equivalent rating - so a 15W CFL might be labelled as '60W equivalent, and everyone was happy [apart from the fact that they were slow to switch on, 'warm up' and to colour of the light they gave off was (to most) not what the doctor ordered]
Now, with LED lighting, the old 'power equivalent to an incandescent bulb' just doesn't work. The reason for this is mainly because LED bulbs keep on getting brighter for a given power usage, as the technology improves - but its also because LED lighting tends to be directional, so the amount of useful light depends on the 'spread' of the beam as much as the power or efficiency of the light fitting.
You see with old incandescent and CFL bulbs, the light mostly spread out in (almost) all directions. This meant that, depending on the light fitting, a lot of it got wasted. Sometimes the 'all around' nature of incandescent and CFL bulbs was useful but mostly it meant that countless different kinds of 'clever' or 'stylish' light fittings were required to make the light useful and/or add character.
With LED lights good design of the light fitting is still required to make the most of the light - but the design possibilities are greatly extended and its much a much better technology for creating character and putting useful light where its needed.
So, back to the original problem. How much light do I need and how can I measure it?
Step up Mr. Lumen. Your time has come!
Scientists, Architects and lighting designers have been using Lumens to measure light for a long time and - like so many things in Science - we could get all technical at this point and talk about the different 'kinds' of Lumen, the wavelength of visible light and all kinds of other things, but here we just want to present the information that we think you'll find useful and might even stand a chance of remembering.
The most important thing you need to understand is the the Lumen is a measure of the TOTAL light. What we're actually also interested in is the AREA over which the light is spread. So 400 Lumen might light up my desk so that I can easily read a book - but its not going to do much to light up a whole Cathedral so that everyone in it can read their Hymn book.
So here's what the clever scientists and lighting designers have come up with:
So, for example, in a domestic environment 300 Lumen per Square Meter (L/m) is OK for a Hallway, 400 L/m is what you need for Reading but you'll want 4-500 L/m in Living Rooms and 5-600 L/m in Bathrooms: And 7-800 L/m 'task' lighting in Kitchens/Bathrooms etc.
You'll find more and more LED manufacturers and retailers quoting Total Lumens for their light fittings. Simply relate this to the lighting level you think you need in a particular application and take into account the area over which you want to spread the light. The sooner you get used to this the better - it'll brighten up your life for sure....