One spectrum lights

Can I grow a good autoflowering plant(auto assassin) with just 2700k spectrum, because it's almost impossible to get 6500k spectrum CFLs in my country, and ordering on the internet will take some time because of shipping.

id go buy watts and not kelvins to confusing. 100 watts per plant is what is most common for bare minimum

yes you can it will take longer to build up a large plant (veging) so flowering will start on a smaller plant and probably give you less yield. You could compensate for this by vegging 24/0 and hopefully it would floweri at that time level too so it could soak up as much light as possible.

yeah you can, its best to use more 6500k for veg, and more 2700k for flower, but if you've only got 2700k's to work with its not a deal breaker...just get the highest wattage you can get possible, and as many as you can...the lower the wattage the closer you have to keep them...the 23wattish bulbs you want to keep about 1-2" away max. If you are growing in a very confined space even CFL's will heat it up, so be sure you have plenty of ventilation.

Also don't forget about your soil(if you are planning on doing soil)...make sure its light and airy and drains well(i.e. is dry after 2-3 days and starting to crust over).

Good luck!

I am planning to make 0,9m x 0,9m x 1,3m(height) growbox. It will be for one plant. So I need ~8000lumens = ~135watts. Am I right?

sounds about right...that should work just fine

Huge thanks for the answers!

Those color temperatures are the plant's weather forecasters.
Red is cloudy, the plant gets itself ready to process water.
Blue is clear skies, the plant closes up for hot and dusty.
These are just two inputs out of many. An influence.

Most important is enough light (posted already), the supplement lights are just that, supplements. Cloudy readies the plant to use the water and nutes faster. Clear sky and the plant hunkers down and closes up more.
How the overall grow is being conducted affects how strong the red/blue ratios come across. Influence is less when the light is dim, the plant stretches towards any color available.

2700K is multi spectrum, a smaller blue/green line than 6500K is all.

A 630 nm LED would be single spectrum. LED builders usually add a little more color, not always much, but some. Most of their hype is how much of what spectrum is added.