Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



LED strips with very monochromatic lights

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,113
Points
113
I got this led strip some time ago: WS2811 RGB LED Strip Light Addressable Digital Tube DC5V 30LED M White Black US | eBay

Putting it to use it found it very difficult to get a warm white light out of it. Regardless of how i tweaked the balance between red, green and blue it never got to a really nice color. Looking at the output through a grating i found the colors to be very narrow band.

Is there a way to tell which led strips will have that issue? I have some other adressable led strips that seem to use much more broadband leds. They are totally different though, running of 5 volts instead of 12 and adressing each led individually instead of in clumps of 3.

The first strip is very good for producing strong primary colors obviously, i wonder if that is intentional. The listing really doesn't mention it specifically, but it almost looks like these leds were designed for tv backlights rather than general purpose. They are cheap and pretty bright though, so some people might really like them as long as it's not for general lighting.
 



Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,113
Points
113
RGBY leds seem like a good solution, but it does not explain why some strips are very monochromatic and others are not.

Getting a replacement strip or two is not a problem, but perhaps these strps are good for people that actually want strong colors ;)
 

ElectricPlasma

Super Moderator
Staff member
Joined
Dec 11, 2015
Messages
1,628
Points
113
I've never really seen good RGB LED strip lights that give off a nice white light, even those standard single RGB LEDs do a better job than the flat mounted ones IMO. The RGB ratios just don't cut it for me no matter what, I always see at least a little bit of the separated colours. Also with some drivers, having those LEDs on white can cause terrible flicker, enough to be noticeable by your eyes and almost obstructive on a camera. I'd take a look at those very condensed/compact RGB LEDs, maybe those would do a difference but I'm not too sure.
 

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,113
Points
113
It varies a bit. Flicker is no problem with these leds, they are WS2811 driven, pwm should be at least a few 100 hertz. To the naked eye its completely invisibe, filming at 240 fps shows some beading.

As for the color: I have set the rgb ratio to about 4:2:1 (experimented to see what looks best). I used a IR remote dimmer on an arduino, it ramps the power up in this ratio until red is at 255 and then just keeps going until all colors are maxed out.

By the time you get to full power the light is quite bluish (and bloody bright), but that's okay - it's intended as background/orientation lighting, full power is just there in case i want it sometimes.

Perhaps i'll give it a try with the RGBW ones. I'd like to use them in more places, and make it such that dimming gives a warmer color temperature on lower settings. Software seems to be the easy part now, kinda cool what you can do with IR or even wifi control :)
 

Bionic-Badger

Well-known member
Joined
Oct 26, 2007
Messages
5,463
Points
83
There are those RGBW LEDs that are pretty nice. Have you also done some gamma correction and possibly used a library that does dithering (e.g. FastLED)?

The dithering seems to work better for LEDs like the APA102-based LEDs and their higher PWM frequency. They seem have better color reproduction in general.
 

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,113
Points
113
I have not tried dithering, for now the 255 levels are enough, unless at very low brightness levels. These leds are the individually addressable ones (neopixels) so i don't have much control beyond their internal pwm unless i update that really quickly (can be done).

I might look at the RGBW strips though, seems useful to have that broadband orange-yellow output of the typical white led in the mix.

Another thing i might try is to use some diffuser material (like the stuff they put around small diameter TL in bathroom fixtures on the top of the mirror and such). Up close you can actually make out the individual color points from the dies now.
 

Bionic-Badger

Well-known member
Joined
Oct 26, 2007
Messages
5,463
Points
83
Yeah, some those IP67 strips have a small bit of diffusion. They certainly don't look as sharp as the IP-65 type
 

Benm

Well-known member
Joined
Aug 16, 2007
Messages
8,113
Points
113
I have some other ones that are waterproofed by a rubbery enclosure (not bonded to the strip, just a sleeve that you could remove), but that is pretty transparent. They are different leds though (individually adressable, 5v supply instead of the other strip that addresses by clumps of 3 and takes 12v).

One downside of the 5v stuff is current draw - i have 2 meters of the stuff, 60 leds/meter, and powering that takes 3.6 amps at full brightness.

This is doable, but if i want to do something like a 8 meter run along the living room it might get problematic (in terms of cabling), or i'd have to limit the power in software.
 

Bionic-Badger

Well-known member
Joined
Oct 26, 2007
Messages
5,463
Points
83
Yeah, it is kind of a pain that way. I usually limit my strips to about 50 led (mine are 30/m) so that there isn't a huge variation in LED intensity due to voltage drop. That makes it about 300W per 20x 50-LED strips (30LED/strip). You can usually get away with less though, since that's for full-on. I often assume I'll only be lighting up about 50%-66% of max power at any given time.

For long distances, a friend of mine put DC-DC converters along the way with a 24V trunkline to tap off. It cost a bit more, but seemed to work pretty well.

For dithering and such, I've had pretty good luck with LEDscape on the Beaglebone Black, and to some extent the FastLED library with a Teensy. The LEDscape on the BBB can push about 400-500 fps on 48 50-LED strips so it has a lot of room to do temporal dithering. It also does gamma-curve adjustments. I'm generally pleased with the color reproduction using that.
 




Top