Looking at the different types blinds available all of them offer a blackout option to a different degree. Some only meet that description in the sense that it blocks out a percentage of the light coming into the room. Letís look at the different types of blinds and judge the performance of each.
Vertical Blinds are the least likely of any blind to bring a substantial reduction of light into the room. The reason being is the way they are designed. Letís look at a window say 100cm * 100cm with a slat size of 89mm. There will typically be 14 slats of fabric on a vertical blind that size, each slat overlaps the slat next to it allowing a certain amount of light to come through. Taking into account there are 14 slats, light will be coming through the blinds at each overlap. Hardly the best option even if the fabric itself is blackout.
Venetian Blinds and Wooden Venetian Blinds encounter a similar problem; there are essentially a number of slats overlapping the one next to it, allowing for light to come through. Although the normal venetians close tighter to the slat next to it than even the vertical blinds, itís not tight enough to stop light coming through. Wooden Venetian are probably the worst slat type blind to block out light due to the thickness of the wood causing the gap to the slat next to it not intended to be tight closing.
Roman Blinds are in my opinion the second best option for a blackout blind. They are the most stylish giving you the option of style as well as function. The lining used on the back of the main fabric provides the blackout function, therefore not interfering with the design. They also fit the tightest into the recess where the blind is fitted, preventing hardly any light coming in at the sides.
Roller Blinds ranges typically offer the largest choice of fabrics option but again due to their design allow too much light into the room. The size of the brackets used to hold the blind up results in the width of the fabric being around 33mm narrower than the width of the blind including its brackets, therefore allowing light into through that 33mm of the window recess.
Finally, the best option is a Cassette Roller Blind. A roller blind is fitted inside a typically white powder coated aluminium frame. The frame fits snugly in the window recess and the fabric providing the blocking out of any light. As the frame prevent any light coming through the sides, top or bottom of the blind, it gives you the complete solution for a blackout blind.