Some advice on which lamps or bulbs to use.
Use LED lamps with a screw-in E27 or E14 fitting and a frosted glass or plastic outer bulb for diffuse light, or clear bulb with filament look or calex pearl dots if you'd like a more decorative look.
LEDs give off a much clearer, more pleasant light than CFLs (compact flourescents) and are more efficient than a lot of other lighting. E27 fittings seem to have the biggest choice available and they tend to fit more reliably than bayonet. E14 come in smaller sizes which can be very handy. Some LED bulbs are dimmable and some aren't, choose carefully if you have a dimmer.
The Ethel and Polly Standard Lampshades have been tested for use with 100W incandescent bulbs but there is no need for incandescent these days. They use far too much electricity and give off plenty of heat which will affect the lifespan of fittings, cables and diffusers. I don't recommend using these older bulbs, but instead recommend an 'LED' (Light Emitting Diode) bulb (which gives off a good clear light). Use either E27 (also called 'ES' / 'Edison Screw') fitting or use reducers and E14 (also called 'SES' / 'Small Edison Screw') fitting with all Ethel Polly and Cube products.
Ethel Lampshades needs a lamp which is no longer than 130 or 135mm total length for a nice even glow through the diffuser.
The Waisted collection uses E14 fittings, and has a max 10W rating. The Whip collection uses E14 fittings, and has a max 4W rating. E14 LED bulbs are available from IKEA (frosted), Philips (frosted or clear), Calex (clear) and Bell and many others.
OFT favourites 'bulbs' / 'lamps' for different products:
For Ethel and Polly Pendant shades: Philips: E14 ‘P45’ 5.5W LED 2700K (frosted).
For Waisted and Whip products: Xanlight: E14 2.3W LED filament 2700K (clear with 'filament' look).
For Waisted Table Lamp: Calex: E14 1.8W LED 'Pearl' 2700K (clear with interior tree of spots).
For Polly and Ethel Pendants: IKEA: E14 'LEDARE' 8.6W (600lumens) LED 2700K (frosted).
For Cube, Ethel and Polly pendants and lamps: Philips Hue White LED E27 Light Bulb, 9.5 W
For COLOUR in Cube, Ethel and Polly pendants and lamps: Philips Hue White and Colour Ambience Wireless Lighting 10 W E27 Richer Colours LED Light Bulb... plus any necessary controls.
For Cube Polly and Ethel floor lamps (and pendants if using E27): IKEA: E27 'LEDARE' 6.3W (400lumens) and 8.6W (600lumens) LED 2700K (frosted).
E14: Philips 6W MasterLED Candle, LED. 470 lumens (75 lm/W), warm white, 2200-2700 K. Dimmable.
Light levels: Lumens are a measure of light given off.
This table compares older incandescent with newer LED lamps for reference, showing how many lumens the different wattages of lamp give off.