My paper Gran Larousse Català defines 'cegar' as:

Obstruir, tapar o tancar una obertura amb terra, pedres, una paret, etc.

E.g. 'Van cegar una de les entradas del metro'.

Black out roller blinds can be very helpful in controlling the intensity of the light, the smaller and higher the light source, the more half tones you see in the subject.

http://willkempartschool.com/art-studio-lighting-design/

blacked out

tr) to obliterate or extinguish (lights)

http://www.thefreedictionary.com/blackout

--------------------------------------------------
Note added at 5 hrs (2015-02-17 19:23:04 GMT)
--------------------------------------------------

The Digital Gallery is specially designed to allow for total black out or low lighting. Principally this allows for two uses, for audio-visual or digital media work where a darkened space is necessary, or for work which is extremely sensitive to light, such as older works of heritage value. The space has enhanced access to both power and data in the many floor points located throughout the room. Total blackout is achieved by the use of large blackout drapes at both entrances, which when walked through create the least amount of light bleed into the room as possible.

http://www.visualcarlow.ie/about/galleries/

--------------------------------------------------
Note added at 5 hrs (2015-02-17 19:25:59 GMT)
--------------------------------------------------

Blinds for roof windows and bedroom skylights offer a wide range of benefits: you can enjoy privacy and complete blackout, gain control over the amount of sunlight entering your room, and even lessen the noise of rain. Once you have roof blinds, you’ll never go back. The perfect blind will not only fit your roof window, it will complement your room’s décor, be easy to fit and help make your living s pace as comfortable as possible.

We have various blinds available for you, including regular roof window blinds and motorised blinds to fit on your electric or solar roof windows. Whether you’re looking for the ideal blinds for VELUX windows, something to completely blackout the room or external roller shutters for added security, we have something for you. We have FAKRO blinds, VELUX window blinds and many more from your favourite brands.

http://www.sterlingbuild.co.uk/products/blinds