Is there a general FAQ?

Short time lurker first time poster. I’ve recently gotten interested in the world of LED flashlights and found your forum which seems excellent.

I’ve recently gotten into mountinbiking and am looking for the perfect MTB light now that fall and winter is upon us. I’ve read quite a few threads here and on other forums trying to get a general understanding of the topic but haven’t found a good FAQ that explains how you go about finding things out. There’s so much I’m wondering. So, if you know of a good introduction FAQ please point me in the right direction.

I also have a few general questions.

- How do you know how hard a LED ought to be driven to not overheat the case?

- In general, is it better to have more LEDS with less amps or fewer LEDS with more amps? Is there a formula?

- In general, is it better to have more reflectors or more LEDS, ie a 1 LED per reflector in a 2 reflector setting or a 2 LED single reflector lamp?

- Is it important to know how much current a lamp draws (or is it pulls)? Most lamps on fasttech don’t have an amp rating, some do, do you always mail and check before you buy?

- How do you know if you can change the driver in a lamp?

  • Do most lamps have undervoltage protection or is it rare in cheaper lamps, is there a way to find out or do you have to mail the seller?

  1. That depends on the heat-sinking of the host you are using. Some hosts have a lot of mass and good thermal contact via a pill, while some have a very limited heat-transfer path. Using the cheap P60 hosts as a reference, the 501b has poor heat-sinking potential due to a large amount of empty space in the head and relatively little mass around the drop-in, so as a rule of thumb, I only use that host with drop-ins drawing about 1A or less. With a better heat-sinked host, I'll use a higher-powered drop-in with a 3A-driven XM-L.
  2. LEDs are more efficient at lower temperatures and run cooler at lower amperage so it would technically be more effiecient to run more emitters at lower current. Multi-emitter lights can be limted by a number of factors, including driver design, and reflector design. The majority of multi-emitter lights have very shallow reflectors which limits the throw potential of the light. Generally speaking, multi-emitter lights will be more floody while a single emitter will produce a much tighter and throwier beam.
  3. Yes, current draw is important. Read reviews, and familarize yourself with Ohm's Law. Power(Watts) = Voltage(Volts) x Current(Amps). If a lamp is rated at 10w, and it runs from a single-cell, you can calculate the amperage easily using Ohm's Law (10W = 3.7V x ?A -> 2.7A). Keep in mind that the numbers won't be exactly what an emitter will see since you will have loss in the circuit and the driver, but it will get you close to what to expect. And that's all assuming that the specifications listed on the seller's site are correct. It may have a 10W emitter but that doesn't mean it's driven at full power...
  4. The most common driver size used is 17mm, but many lights used larger or smaller drivers. Many of these are replaceable, but it can sometimes be difficult to find drivers that fit while meeting the voltage/current requirements of the host. The best bet to know for sure is to read reviews and see what others report. In some cases though, designs may change between variants so a light may look like the same design on the outside but have a different pill design and different driver.
  5. Most of the cheaper ones I have don't, but a lot do. I've been surprised by a couple of my lights before when they did automatically drop to a lower mode due to low voltage. In most cases, I wouldn't trust the seller to know for certain if their lights do have low-voltage protection. I generally keep my cells charged up without running them low enough to trip the low-voltage protection. Most of my lights have had drivers replaced with drivers that do have low-voltage protection...

Oh, and Welcome! Laughing

The very excellent "Flashlight Wiki" ( has a LOT of very useful information in it. Be sure to check it out!

Be sure to read (link to the left on BLF) (Ah, Keltex edited his post and added this!). Basically you'll want to grow in knowledge by following reviews and such. Don't trust Chinese sellers unless BLF'ers have vouched for them (that goes for buying from them or trusting their specs). Read reviews! Search for reviews on lights that interest you. Don't be afraid to post asking if anyone has the light you want and to provide input on it.


Thank you, I’ll start by reading the wiki and then som more threads. I feel more questions are incoming. :slight_smile:

If you have questions, then this is the place to ask them! 8)

Hmm , perfect MTB light….
Well I use a LEDLENSER MT7 , mainly as I can adjust the light to suit the trails, as it is a zooming light you can adjust the lens for more throw vs floody side light, some guys use two lights, one on the handle bars , and a head light so the beam ideally is we’re you look , this is helpfull with twisty trials , next is how long you intend riding as this affects run times, and the type of battery to be used, cold temp affect certain batteries.
I’m going to be testing a Roche F12 with my LL Mt7 soon, ie the Roche for flood and LL for throw.
Fasttech is a decent source for budget bike lights., you may want to consider a light that has an external battery pack like These

I do mods based on the Vistalite nightstick sets but other brands work well also such as Marwi. In a bike light mass needs to be minimized to keep weight down while having good surface area to take advantage of the airflow. The use of low out put at low speeds and higher output at higher speeds goes hand in hand with this concept. The choice of emitters in both number and type will relate to the battery and driver combination you choose. The more emitters you use the smaller the optics you’ll have room for making for a more floody beam. One emitter allows for a deeper optic that can throw farther. I use both, a floody beam on the handlebars that can light the width of a single track at 2-3m or the whole road at 10m and a medium spot beam on my helmet that is 3-4m wide at 20-25m and lights where I’m looking. Today’s LEDs are capable of doing either with a single led and different optic. A larger led like an XML would make a good bar light and the xp-g2 a good helmet light. Both driven at 2-3A would produce enough light for most off road situations but for really serious night shredding I’d reccommend two bar lights with either triple xp-g2’s or single XML’s and another on the helmet. Power down on the ascents and power up on the descents. 8) My favorite optic is the Ledil 35mm cute-3 that mates with 3-up boards from Cutter or with PilotPtk’s led driver combo using med and spot lenses but that preference is largely based on how it fits the Vistalite lamps I use.