I want to build my own ceiling lamp with WS2812B LEDs (like the one in the picture).
Is there any rule of thumb to calculate how many LEDs I would need to get the brightness I want?
My current standard lamp has an OSRAM 15 Watt lamp with ~900 lumen according to the specs.
But it would be nice if my new lamp was brighter, of cause.
Any experiences or calculations you can point me to?
This thread says ~6.8 lumens per LED for full white brightness. Though I would derate that.
https://forums.adafruit.com/viewtopic.php?f=8&t=44064
If I am reading this datasheet correctly, it claims almost 13.5 lumens per LED (402 lumens/meter @ 30 LEDS/meter) at full blast: http://sirs-e.com/wp-content/uploads/2008/04/5050-LED-RGB-Data-Sheet.pdf But these guys only claim 3.14 lumens per LED: https://www.superbrightleds.com/moreinfo/surface-mount-smd/rgb-5050-smd-led-120-degree-viewing-angle/322/ So, probably more than 2 lumens each but less than 10? =)
So, there is no easy answer. 
I guess I will just test it for myself then.
I just hold my phone 1m under my normal lamp and got ~110 lux.
My LIFX smart bulb has 180 lux.
A 1m WS2812B strip with 60 leds got 120 lux with an opaque casing and 150 lux without any interference.
So I guess I can use that as a starting point and build a prototype where I can test and measure the brightness before I mount the final lamp to the ceiling. 
But thanks anyway!!
Be careful with full white RGB leds, they can get really hot. You don’t want to burn them out!
For reference, I made a ceiling light with about 300 LEDs (SK6812 WWA), and it was not bright enough to be the main light in the room. Somewhat of a guesstimate, but I think you’d need 1000+ LEDs to really provide the primary lighting for an entire room. And definitely look into the SK6812 WWA for variable white / amber color, if you want to light a room, since the “white” produced by typical RGB WS2812s is very blue, and not so pleasing as a main light source.
@Mike_Clifford
Thanks for your reference.
That is a lot of LEDs. 
I think I will build a prototype to get some experience with the brightness.
I was thinking about RGBWW, too.
But FastLED does not support this yet, as far as I know.
@Christoph_Wempe I went down the same path of thinking regarding use of RBGWW lights so that you could get the best of both both worlds (pleasant white light and RGB fun), but decided against it due to lack of FastLED support. I ended up going with the SK6812 WWA (since they program just like WS2812s and have only 3 LEDs per cluster, warm white, cool white, and amber). If interested, you can see it in action here: https://youtu.be/g7A8h72RwdY
Great video and beautiful lamp!
But now I see, why 300 LEDs were not enough for you.
My Room is much smaller than yours. ^^
Thanks! And yes, it is a pretty big room. Best bet is to just get some LEDs, test them and see if they give out enough light for your liking. If not, can always add more 
That’s the plan…