Fenix store has diffuser lenses that fit some diameters and there $6 ish
If you get the 501b let me know how good it is 
The DX 501b have red XR-C at least the one I ordered did. Typically red diffuser lens used on white leds will severely deplete output.
Really appreciate getting more input. Apparently the DX reviews say something about Crees instead of the spec’d LED . . perhaps the product is slowly getting updates based on led cost and availability.
Edit - I guess the other question is if you got an XRC, did you get something worse than they spec’d? My quick review suggests the K2 might be much better than the XRC?
The DX ad IIRC states Luxeon K2. In the last year or more Cree have been sent. The Green I ordered had a Cree XRE. The Red had Cree XRC. Guess my older Cree pdfs are out of date as no Red XREs are listed. Read the newer pdfs and suprise RED XREs. Mouser or Ledsuppy doesn’t list them. Who has Red XRE stars?
Always something new and in a quad die. Where can I get one?
I picked up a PT121 red less than a month ago. 2000+lm
http://www.luminus.com/products/PT-121.html
Built a green PT120 aspherical last fall.
That thing looks just like an MCE.. havent seen them for sale anywhere tho.
I’m pretty sure they can be purchased direct from led engin. There is a phone number on that link to request quotes.
“I picked up a PT121 red less than a month ago. 2000+lm”
Nice! 2225 red lumens @ 30amps. I would love to have one of these built into a drop-in of some sort for one or any of my lights. Not in either of my Hellfighters, obviously.
Been getting my PT54 reds from DTRLPF for a while. Currently he has new pulls cheap 6@$50 on Ebay.
Mouser has LED Engin @ $36 + s&h.
I bought a red xre from goodluckbuy.com havent used it yet. I also ordered the green xre from goodluck and installed it in a small sun c10 flood to throw and its pretty sweet. It throws good, throws easy 500 feet.
Havent tested the light out in the field with a scope but should be more then bright enough. Its only driven at 1.1a but thinking of doing either direct drive or a 1.4a single mode driver i have.
Willie is the man on colored leds.
Installed that pressure switch on the small sun that you suggested to me and works good.
Posted on iphone
edited on PC
This is the brightest RED light i know of it won’t be cheap but a red SST90 should be a bright as your going to find anywhere
This is very interesting. Wouldn’t mind having one.
Lambda has inspired some of my direct drive builds. The SST90 is actually a little less powerful than the PT54 and is no match for the PT120/121 series.
This was with a 8A build.
And PT120 green build.
While that is definitely a good start, I found that my ET T20C2 MKII XML with a red filter isn’t nearly as bright as using the red LED drop-in in the same light. I use red and green frequently and have been thoroughly pleased with the red drop-in for my EagleTac. 
Some really great stuff here . . . great pics on I think it was the TR1200 build or next link, willie! Did you ever do a thread on building those feeder lights? Solar powered?
How about one of these 5 XRE lights and we swap them all for red XREs that would kick some serious ass.
Just finished soldering a triple XP-E red (in N3 bin) to a modified (so each LED is individually regulated to 700mA) 2.1A driver. From the specs it should be between 300-330 lumen. All I have left is to get a P60 drop-in shaped piece of aluminum machined out and I will have a 50m+ bunny torch. Awesomely bright for a red torch however the soldering took me many hours to get right. I will stick so photos up if I ever get it finished (I started at least 2 months back).
As far as I am aware the XP-E N3 bin is the best there is when it comes to efficiency vs red output. It is about 62 lumen per Watt. Wavelength is 620-630nm. I got mine from Cutter electronics in AU.
Really not much to build them. I used two 3up XPC (typo xre in post) & and a 1400ma buckdrive from ledsupply. Wired the 3up in parallel to each other for a conservative 700ma. Put a switch on the buckdrive to toggle a resistor to 350ma for everyday use. Only run with 700ma when hunting that stand to minimize battery drain. Lucked into the following 48w panel and 85lb large AGM battery for CHEAP. The brains and control is a solar street light controller that regulates the over or under charging of the battery and is programmable for runtime or dusk to dawn. Uses the solar panel for a light sensor. One like this.
http://www.ebay.com/itm/10A-12-24-Auto-Distinguish-Switch-PWM-Solar-Street-Light-Panel-Charge-Controller-/280882460728?pt=LH_DefaultDomain_0&hash=item4165e63838
On my smaller setup have used this
Found most of my panels and batteries used for cheap local on Ebay, Craigslist as shipping kills most deals on these items.