In the “old days” we got into the habit of using “watts” to mean brightness or light output.
There was only one type of light bulb available in those days: the incandescent (filament) bulb.
We all knew how bright a 100 watt, 60 watt bulb was.
This was/is a misnomer.
“Watts” is a measurement of power usage (volts x amps = watts).
The old fashioned filament bulbs were very inefficient.
Nowadays, there are much more efficient ways of producing light, which is actually measured in “lumens” (see below).
Light Output LEDs CFLs Incandescents
Lumens Watts Watts Watts
450 4 - 5 8 - 12 40
750 - 900 6 - 8 13 - 18 60
1100 - 1300 9 - 13 18 - 22 75 - 100
1600 - 1800 16 - 20 23 - 30 100
2600 - 2800 25 - 28 30 - 55 150
So a 13 watt LED bulb will give you the equivalent light output (1300 lumens) that you would previously have from a 100 watt incandescent bulb.
It will last many times longer and use a fraction of the electricity.
UK and EU law states that we must label the lamp holder with a permanent stating the maximum wattage of the light bulb.
Although, the old incandescent bulbs are now banned by EU law, they are still available if you know where to look (due to “loopholes” in the law).
Therefore, the maximum wattage is based on the most inefficient light bulb available to consumers.
Sorry it is so confusing.
Can I suggest that your customer uses the chart above to work out how much light she requires and then buys her bulbs accordingly, based on “lumens”.
CFL stands for Compact fluorescent lamp.
I would avoid them (they take ages to warm up) and go for a warm white LED.