If you are saying you want to keep the sheers underneath and add black out drapes you will need a double curtain rod....

Get solar shades for heat and sun control they allow you to keep the view and are pretty affordable too. They roll up on cloudy days if you like. IMO a much better product for this purpose and the bonus of keeping the view.

I live in California (Zone 9b) and all of my windows face WSW. They get lots of direct sun and it gets very hot. I'm trying to figure out the best way to protect my plants while still getting maximum growth. When I just let the sun in through the windows I get lots of light damage on the leaves, color fading, and overall plants that show signs of heat stress (not all varieties, but many do.) I recently installed sheer curtains (sheerest I could find!) and I am no longer getting any leaf damage, even on more delicate plants, but I have noticed a substantial slowing of growth. Everything looks happy and healthy, they just are not growing nearly as quickly as before. The advantage of curtains over window film is that I can simply leave them wide open during winter whereas the film would remain in place year round. However, UV is not considered to be part of the PAR (photosynthetically active radiation) spectrum so theoretically this would not affect plant growth. Now I am wondering: Will installing a UV blocking window film provide enough protection for my plants and yet allow for a greater amount of light to pass through? It would be amazing to just allow the light to pour in without worrying about it being too intense. The window film will certainly create brighter conditions but I am not sure if the light will still burn some of my plants and cause heat stress. The other downside to UV film is that when I open the windows, the lower section is completely bare other than the window screen, but I can still use the curtains when I have the windows wide open. Can anyone confirm that UV film has allowed them to grow plants (especially variegated ones) right next to the window all year long without damage or heat stress? The layout of our rooms (long and skinny) doesn't really allow for freedom of plant placement; they either go right next to the window or they don't get any light at all. If I can get my hands on a small amount of film I will apply some and take readings with the light meter but I'll need to test an entire room for a few weeks to gauge light/heat stress. I'm hoping someone has already done this experiment and can offer their wisdom! I'd greatly appreciate anyone who can share their experience with this!

Sheers usually need to have the most fabric to look luxurious. I'd go with 3X, at least 2.5X.