Being stuck right now with days of grey summer rain I was looking around to light up my mood a bit and found an Instructables that might just be able to do this: the Electric Umbrella from sockmaster.
The project is fairly simple and good documented in the Instructables. What’s needed to bring sun shine into the rainy days is a couple of LEDs, a variable resistor for dimming the light output and switch the light on and off.
As outlined in the Instructables if you use 3 volt LEDs there is no need to add resistors for the LEDs but if lower powered LEDs are used it’s not that difficult to add them. As eTextile expert you might replace the wire with conductive yarn which will give even more flexibility and I guess also more robustness to the LED grid which needs to be fixed inside the umbrella fabric.
Scanning through the comments of this Instructables there is a suggestion to maybe ass solar panels (small, flexible type) so the umbrella can be used to give you some protection when the sun is burning down and charging the batteries to power your private sunshine during rainy days.
The solar panel addition will increase the complexity of the project greatly but on the other hand, it’s a cool idea to hack an umbrella.