I know some of you have purchased the Ultrafire WF-501B Flashlight from Deals Extreme: https://dx.com/p/ultrafire-wf-501b-ph...2-cr123a-20333.

It seems to be pretty inexpensive, and I wonder if it's also durable. If you have one, how long have you had it, and how has it functioned?

Also, what size lens does it take .... is it 27mm? I'd like to get a wide angle diffusing lens if I get the flashlight. I know that there are some diffuser lenses available.

Don't know about durable, but the link you posted is for a flashlight with a now discontinued Luxeon K2 red LED which I believe puts out about 75 lumens. Thats already pretty marginal and if you put a spreader on it it'll just spread those lumens over three times the area and make it even less conspicuous. Are you looking for a tail light or a headlight?

Well, I've got three of the Ultrafire WF-502B Red LED lights that are being shipped to me from another dealer then DX that haven't showed up yet in the mail. As far as I know they are the next model out where as the 501 is the previous model. I also have some diffuser lenses that are suppose to fit it on order. Also the 502 uses a Cree LED and depending on who's listing you read is rated between 140Lm and 210Lm so I'm figuring I should get an honest 100+Lm out of it.

I plan on posting my results once everything shows up in the mail and I get them mounted on the back of my bike.

turbo1889 or others: if you find a similar strong red led flashlight that can use AA/AAA batteries, please tell me here. Thanks in advance I've looked for a while and haven't found one, only mini ones.

I'd like to experiment with one of the red LED flashlights on my commuting setup as a taillight. I had read that they are 200 lumens, but those are the LED rating and not OTF lumens (and maybe I had read about the 502B instead of the 501B). According to mechBgon in this thread, post #20, he described it as "the most intense red light I've ever had. If it were aimed precisely, it could be good to have in dense fog." I'm new to thinking about these LEDs, so forgive my ignorance in not knowing the 501B had been discontinued.

Cool. I'd like to know how this works. They are about $17 on Amazon. Which lenses did you wind up purchasing?

Hi Timmy - no need to apologize - I was just trying to help out and that doesn't mean I'm always right. Just to clarify - its the EMITTER that has been discontinued by Phillips. https://www.philipslumileds.com/uploads/54/DS51-pdf
That doesn't mean there isn't stock of that LED availabe anywhere - it just means Phillips has has stopped making it and replaced it with something more effective. DX may be buying up old stock from a variety of sources. But that particular LED is available in three different BIN designations in red and DX has the annoying habit of quoting the specs for the highest BIN while using the other(s) for actual products.

I did do some comparison shots using the same camera settings and am pretty sure you're not even looking at 75 lumens. That would be pretty good on its own if aimed carefully, but its effectiveness (intensity) would drop with a spreader. That doesn't mean you might not be OK with it - hard for me to know what 'OK' is to you. For $12 it could be OK if you're looking to spend less than $20. Thing is - compared to pics I took of a $60 Serfas TL 60 (60 lumens) taken using the same settings - its very underpowered. If in doubt - why not simply drop mechBgon a line directly? He's a nice guy and could probably answer your questions with more definitely.

Thanks. I've never purchased from DX. I normally do a Amazon-to-Ebay head-to-head test on pricing to gauge the market. I will use google after that to see who has what.
I just ordered a Solas to up my "blinking" out the back. This blog review puts the Hotshot on top, and this review as well as the first Amazon review (same guy???) but the Solas above the Hotshot. I think I've got enough OTB (re: OTF?). I've got a BM Brakeline Plus back there too, and a PB Blinky 7 on my helmet. I'm just curious whether I can get something that really lights up the back for about $20. Like I said, I know little about the LED technology available, but it's there, and it's really becoming economical. If you can increase you're safety level for about $20, why not?

If I had emailed mechBgon directly, I'd lose the collective knowledge of the forum, so I'd have missed some of the points already made. While it's time consuming for everyone, I learn more as do others, and that's what BF is for.

We've use this on one of our bikes, as the primary tail light. We have a blinkie on there as well, as a back up in case it's dark and/or the Ultrafire's battery is drained.

On the road it appears distinctly brighter than car tail lights and stands out clearly in the daytime. We always have it on. No problems with it after 1+ years' occasional use.

This is the brightest tail light I have short of the Dinotte 300R.

My top recommendation for improvement would be a lower mode for the light. The switch is on-off only. You won't want to ride closely behind this after sun down.

And yes, the lens is ~27mm. (I didn't remove the lens to get the most certain measurement.)

OK - so lets see what we can do with this constructively. That Dinotte is a nice light and I think puts out about 300 lumens. I agree that high powered rear lights can be an issue at night and the other issue can be the narrowness of the beam, which can also compromise its effectiveness during the day. Which is one of the issues I'm anticipating with the flashlight. So can you post beam shots with settings to give a relative comparison?

The most effective way I found myself to use a high powered rear light at night is to point it downwards and paint the asphalt behind the bike with it. That gives a MUCH larger, more visible target for motorists to pick out than a small light source - however bright. Bigger is better - but it takes a pretty decent light to do that and while a spreader could make things even more effective - they're not specifically engineered for red LEDs and the pattern isn't quite the same as for white LEDs.

So I do have some 3 watt red spot LEDs here myself which put out 200 to 300 lumens as well as some red spreader diffusers. I also have a couple other red tail lights of lesser outputs. I'll see about posting some shots by tomorrow and lets see if any of the info is useful to the OP. Aside from the limited run time, I really have no issues with the flashlight - the output seems similar to the Hotsot and Shield TL60 which I have myself. I just have reservations about sticking a spreader on it. A second one might be more effective.

I'll defer to mechBgon's beamshot links which include the SuperFlash and Radbot 1000 that are our best blinkies, and the DiNotte 140R, 300R and the Ultrafire red flashlight that are our "be-seen" tail lights. The Ultrafire gave us an inexpensive, third "be-seen" tail light that I happen to have a good way to mount on one bike.

Makes sense. There's also been a recommendation to use a skewer extension to mount a flashlight next to the rear hub, so the flashlight can be pointed back but be farther from eye level.

I payed $12.49 each with free shipping for mine (and they just showed up in the mail today !!! Still waiting for diffuser lenses to show up). I bought mine here because they had them in stock when DX did not and they had a higher customer experience rating then DX does on the google shopping customer experience index: https://www.focalprice.com/LFG03B/Ult...l#.ULGLEoezjsY I ordered on the 1st and they showed up on the 24th today so expect about a month shipping time.

The diffuser lenses I bought are these (from DX because couldn't find the same thing at a better place to buy) because on another flashlight forum people said they will fit the UltraFire 500 series light units if you put them in the recess in the head in front of the existing lens: https://dx.com/p/23-0mm-optics-light-...ss-5-pack-1918 They haven't shown up yet so I can't confirm that completely but the inside diameter of the recess in the front of the head in front of the existing lens in the 502B units I have in hand appears to be about a inch in diameter as best as I can measure with just a measuring tape and not a set of calipers and an inch is 25.4mm and the outside diameter of those diffusers lenses are 24.11mm according to the picture so if anything they will be just slightly loose which is no problem since I intend to glue them in place.

As far as brightness goes, in a dark room the 502B is definitely brighter then my Pelican brand name (white light) LED flashlight which is rated at 100Lm output and considering the brand name reputation of Pelican I think I can safely assume that their output ratings are not exaggerated. Looks to be just slightly more then one and a half times brighter so that would be like 150+Lm in a side by side comparison if we assume that the Pelican light is a true actual factual 100Lm output.

I also need to pick up a 123A blank spacer battery so I can test to see if they will run on a single lower 3.2V LiFePO4 cell. They run fine on two 123A cells either 3.0V disposable primary cells or two of my 123A rechargeable 3.2V LiFePO4 cells or a single 3.7V protected Li-Ion 18650 cell. Don’t have any 18650 cells in LiFePO4 chemistry just 123A size so need to pick up a spacer to test to see if they will run on the lower 3.2V level on a single LiFePO4 cell which is safer, cheaper, more ecologically friendly, and has a longer service life then conventional 3.7V Li-Ion cells. Reason being is because if they will run off of a single cell at the lower voltage level then I want to hardwire them in to a single common LFP-G20 prismatic cell which would give me extremely long run time (that’s a 20,000mAh cell) with the simplicity and rugged reliability that a large single cell with no balancing issues provides as a power supply.

That looks like a better bet for a number of reasons. A higher output AND a much longer runtime!

Ultrafire WF-502b VS Ultrafire WF-501b: what's the difference? one?

The bodies are slightly different; does this make a difference on the bike?

If they have the same LED and the same battery, will the performance be substantially different?

I thought to search, and Google turned up this at Flashlight Wiki:

Do these have different beam patterns?

They claim 120 lumens for the 140r, & 240 lumens for the 400r.
The 300r is advertised as brighter than the 140r, not quite as bright as the 400r.

The answer was not obvious, but in the stuff you referenced.
All of these are UltraFire WF-501B flashlights. Each one has a different emitter, output, and beam pattern. Note that some are red and some are white. The beam pattern is a combination of the emitter used and the reflector or collimator.
https://www.focalprice.com/LFF94B/Ult...l#.ULJNeYl5nTo
https://dx.com/p/ultrafire-wf-501b-ph...2-cr123a-20333
https://www.everbuying.com/UltraFire-...p-p-24295.html
https://www.amazon.com/gp/aw/d/B0050DX6VM

So the 'WF-501B' is more a description of the packaging format than anything else.

You somewhat answered your own question but as I understood the situation from researching what was available in an UltraFire red light LED flashlight the 501B red LED unit is the older model and comes standard with a drop in emitter unit that uses a non-Cree LED unit which puts out less then 100Lm actual real life output. Where as the 502B red LED unit although only cosmetically different on the outside comes standard with a drop in emitter unit that uses a Cree LED that puts out more then 100Lm actual real life output. In conclusion I chose the 502 rather then the 501 because as I understand it the drop in unit that comes in the red light LED version uses a brighter higher quality LED in the newer 502 model. That made the decision for me.

Basically for the red light LED versions the 502B came with a better P60 drop in installed in it in "stock configuration" then the equivalent "stock configuration" of the 501B. It should be noted that from time to time other red light LED drop in emitter units are available that can be installed in most UltraFire 500 series bodies that do offer other options for a red light LED. Here is a five mode 80Lm one that was available but is currently sold out: https://dx.com/p/cree-xlamp-xp-c-r2-5...8-4v-max-26345

I have 5 of these, and they work flawlessly. Also, I've bought 6 of them for family and friends, and they're still in working condition after about 2 years of use. DX shipped the latest lights with this LED, which is brighter than the original Philips one.
On a fresh 18650 battery, the run time is more than 3 hours. I tried fitting a diffuser on one of them, but it just made it less bright, and didn't seem to diffuse the light much.
I should point out that I always wrap the p60 module with Aluminium foil to improve the heat dissipation. https://www.youtube.com/watch?v=0icJvLm5l14
I mount two of them on my rear rack using an old inner tube (see attached photo) and rotating mounts like this one: https://www.ebay.com/itm/250889423307
If you use a regular mount that can't be rotated, the flashlight might be directed too low/high.
You might want to use a thick elastic band to prevent the light from getting lost on bumpy roads! I tie balloons and use them as elastic bands (better than any elastic band I've ever seen! ). Balloons like these: https://www.ebay.com/itm/370694619706