# Noob guide to DIY Lights



## wmac (Sep 29, 2010)

Here's a first stab at it. I figure I can post this in the beginner section and write another for this section as a follow up that is more detailed and comprehensive about the building process itself.

Riding your bike doesn't have to stop when the sun goes down - get a light! There are a lot of great lights for sale, but some prefer to build their own light*system. Although building your own won't necessarily save you money, there is a sense of pride and satisfaction that comes from building your own light system. Before you can start building your own light, you need to understand the different parts of a light system. A light system can be broken down to: light source, optics, power source and housing.

Most modern lights use an LED instead of an incandescent bulb. LEDs are a specific type of semiconductor, light emitting diodes. The reasons are that they are more durable and use less battery power to emit the same or more light compared to traditional bulbs. Light output is measured in "Lumens." LEDs are designed to handle a specific number of watts, so, an emitter that can handle more watts is one that can potentially output more lumens.









Modern LEDs with an emitter inside a hemispherical lens
Photo by odtexas

Building a light with an LED is a little more complex when compared to a traditional incandescent bulb. Remember doing an experiment with a battery and a light bulb back in science class? It was simple. Touch a positive wire to the bulb and positive pole of the battery and a negative wire to the bulb and negative battery pole and you have light.

Well, that doesn't always work with LEDs because they are directional, meaning, the current only flows one way. They also only operate within a specific current range or else: they will emit light inconsistently, they could get too hot or even burn out immediately. The reason is LEDs are current controlled devices and you must deliver a consistent current to the LEDs over a range of load voltages to maximize their potential. To accomplish this, modern LED lights use "drivers" instead of resistors.









Modern drivers are used to regulate current to LEDs
Photo by odtexas

The reason resistors aren't used is because the current and voltage in resistors are linearly related whereas the current flowing in an LED is an exponential function of voltage across the LED. In other words, a small change in voltage can produce a huge change in current. This is important because you want your light to deliver a consistent beam regardless of battery power. With a resistor, it would only limit the maximum current delivered, but would get exponentially more dim as the battery delivers power.*Therefore,*you need to take the driver into consideration when purchasing the LED because overdriving an LED a little will degrade it substantially.

When buying a driver, it should come with a rating that looks like this:*

- Current: 3000mA
- Voltage: 6-18V
- 3-Modes: high, low, fast strobe
- Designed for XM-LT60 emitters

That means it can deliver a maximum of 3,000 milliamperes with a voltage range between 6 and 18 volts. It also has the ability to deliver a low beam, a high beam and a strobe. Notice it says it is designed for a specific type of emitter? The*rating for that emitter looks like this:

280 lm @ 700mA
1500mA - Energy Star Max Drive Current
3000mA - Max Drive Current
6500K - Color Temperature
Lambertian Radiation Pattern
20mm Diameter PCB

This means it will deliver 280 lumens when supplied with 700 milliamperes of current. It can still operate efficiently at 1,500 milliamperes and should be able to handle 3,000 milliamperes before it burns out. So, why not just run it at 3,000 milliamperes?*In most cases, driving the LED at a higher current will not produce substantial additional light. Instead, the junction (the working parts of the LED) has to dissipate the excess power as heat. Heating the junction will decrease its useful life, and can reduce the output of the LED substantially. Heating it enough will cause catastrophic failure (producing a dark emitting diode).

Some may give a rating in volts, like 5V.*These are really not rated to operate continuously at 5V in most cases. It is better to spec your LED in terms of current, not volts.

The "6,500K - color temperature" is a rating to give an idea of where it is on a scale from how white to how yellow, or more natural (like sunlight), the light appears. This is only a matter of preference.

Most modern LEDs are a square emitter embedded in a hemispherical lens. This configuration will emit the light in a fairly even, hemispherical, 180 degree pattern. For the purposes of riding a bike at night, we want to reform the light into a desired pattern using a reflector and optics, also known as a*collimating system.









Diagram of a collimating system for an LED light system

Collimating systems enable you to focus the light in a specific pattern. They are the combination of the interaction of the lens (the glass bubble over the emitter) and the reflector (the concave, reflective, surface that focuses the light) and optics (any magnification of the beam emitting from the emitter, lens and reflector).*A good collimating system will distribute the light efficiently and evenly with the right amount of throw, hotspot and coma for your application.*

The distance the light travels is often referred to as "throw." (For you math nerds, throw is the luminious intensity calculated as the square of luminous intensity divided by .25.)*When you shine a light on a wall, the inner most point should be the brightest spot, known as "the hotspot." The diffused, "soft," light emitting outward from the hot spot is often referred to as "coma," while the light that is lost outside the coma due to diffusion is called the "spill."*

The amount of throw, coma and spill will be determined by the intensity of the emitter and the configuration of the collimating system. *Changing the throw, hotspot and coma is quite simple. To *increase throw, choose an emitter with higher luminance and/or increase the diameter of the collimating system. The depth of the reflector will determine the size of the hotspot and coma. When comparing two reflectors of the same diameter, a deeper reflector has a smaller hotspot and larger coma. Conversely, a shallow reflector has a larger hotspot and a smaller coma.

Reflectors come in various levels of quality. Higher quality reflectors are coated in materials that reflect the light more efficiently. Efficiency is measured in terms of how much light is absorbed into the reflector instead of being emitted forward into the beam. At the bottom of the quality spectrum are aluminum coated reflectors with 70%-80% efficiency. Next are silver coated reflectors with 90%-95% efficiency and at the top are the dielectric coated reflectors with 99%+ efficiency.

Some reflectors are smooth on the inside and others are rippled. A smooth reflector has more throw than rippled one, but, ripple reflectors have a more uniform beam.

The final piece of the collimating system is the protective lens. This is usually a flat piece of plastic or glass that can sometimes have a magnification "bubble" above the LED. This is usually designed to help maximize luminescence and minimize spill.

The next consideration is a power source. The important factors in choosing a battery pack are milliamperes per hour and volts.*Milliamps Hour (mAh) is important because it's the easiest way to distinguish the strength or capacity of a battery. The higher the mAh, the longer the battery will last. Batteries with different mAh ratings are interchangeable. If your battery is rechargeable then the mAh rating is how long the battery will last per charge.

Milliamps Hour is 1/1000th of a Amp Hour, so a 1000mAh = 1.0Ah

Think of a car. Voltage is how much power is being output by the gas and mAh is the size of the gas tank. *The bigger the gas tank (mAh) rating the longer the device will run. If your battery is rechargeable, then think of the gas tank as refillable (rechargeable).

Most modern light systems use Lithium Ion batteries, the same battery technology used in personal computers. They are typically rated something like, 2,500 mAh/3.7V. This means it will output a maximum of 3.7 volts for 2,500 milliamperes hours. The voltage of this battery will drop as the power is being consumed, so, that means the battery power is not linear. If you look closely at the spec sheet, it will say something like: "The voltage of full charge and cut-off discharge is 4.2V and 2.75V."

This is exactly why we use a driver, because, without it, we would have a really bright light at full charge and a really dim light as it nears full discharge. However, using the example driver above, it requires at least 6 volts. In order to increase the voltage of the battery pack, you would put the batteries in a "series" and it means exactly like it sounds. You would line them up positive pole to negative pole. Two batteries would yield *2,500 mAh/7.4 volts (actually it would be 8.4 at full charge). Three batteries would yield *2,500 mAh/11.1 volts (12.6V) and four batteries would give *2,500 mAh/14.8V (16.8V).

Notice the mAh did not change. If you put them in parallel, a different way of wiring them, two batteries would yield 5,000 mAh/3.7V, three would yield 7,500/3.7 mAh, and four would give 10,000/3.7 mAh.

For our use, we would want to put four batteries in a series.*If you don't want a long skinny battery, you can turn them sideways and wire them into a rectangular battery pack, or, any number of configurations to make them fit your housing.

Which brings us to the final section - housing. Without it, you would just have a bunch of stuff flopping around. When constructing the housing, you need to remember lights create heat and you need a way to dissipate the heat. A lot of light systems use "fins" to increase the surface area of the housing to allow the air to touch more places and cool the housing more efficiently. You can also minimize the heat by under-driving your LED or using multiple, smaller, LEDs.

With this information, you should be able to venture into the numerous DIY light threads and at least have an understanding of a light system and how the components work together and why. Now, venture over to the DIY Lights Forum and see if there's a project you'd like to give a try. Good luck!


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## troutie-mtb (Sep 20, 2007)

wmac said:


> Is there a Noob Guide to DIY Lights? I've been lurking and I'm a pretty capable guy in that I have built R/C planes and cars, but for some reason, the DIY light builds seem a little esoteric. I get the builds, I just don't get why one way over the other, etc.
> 
> Any good existing threads or new write-ups greatly appreciated!


one way over another is why its a great forum and brings out the creative spirit in folks .

lots of good threads to look at then decide what would be best for your needs or wants.

Best way is to search for yourself and pick something you fancy than to get others to say which is the best thread for noobs . 
Then if / when you need / want help then folks on here will willingly help out

Yes there are diy guides but most written a few years ago and leds / drivers have moved on in leaps and bounds since .


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## odtexas (Oct 2, 2008)

Just matters what you want. Diy yourself lets you customize beam patterns, color rendition, runt times, size, etc.

If you like multiple light settings, over heat monitoring, battery reserve monitoring, then a driver from url=taskled.com] Taskled[/url] would be needed.

Personally I build with cheap drivers. The ones using the 7135 chips do have built in overheat protection, the chips shut down if the light get too hot. I have never had one shut down though while biking. Crawling around the the attic - yes, biking - no.

Drivers some in boost and buck flavors. So figure leds at around 3.5 volts resistance. Two wired in series gives you a circuit of 7 volts resistance. A 7.4 volt or higher battery would need a buck driver. A 3.7 volt battery would need a boost driver. Buck drivers are more efficient and more common. Not too many boost drivers out there by comparison.

Here is a general how too. It is from the  diy database thread , page 3.



odtexas said:


> Aluminum Square Tubing, 1" SQ {A} x 3/4" ID {B} x .125" Wall Sq. Tube , from  Speedymetals.
> 
> Aluminum Rectangular Tubing, 1" {A} x 2" {B} x .125" Wall {C} Rect. Tube  Speedymetals.
> 
> ...


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## Vancbiker (May 25, 2005)

You are there. There is all the info one would ever need and 10x more that isn't needed but might be nice to know in these threads. 

First thing you need to assess is what you need your lights for. What experience do you currently have with night riding? Access to machinery? Understanding of electricity? Budget? That should narrow your search some. It would be silly for people here to point you to some DIY mega light when you are looking for a commuter light. 

LEDs are changing so quickly that specifics for LED and optic configuration more than a couple years old are mostly obsolete.


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## wmac (Sep 29, 2010)

Cool, thanks guys. I wrote the http://forums.mtbr.com/beginners-corner/noob-buyers-guide-811009.html and the http://forums.mtbr.com/beginners-corner/noob-guide-geometry-bike-fit-handling-826673.html and didn't know if there was something similar. Basically, I know nothing other than very basic things like the difference between parallel and in a series. Red is + and black is -. That a circuit board is a bunch of wires on a board. Mah is the size of the gas tank and volts is the power output. Putting batteries in a series increases power. There is a difference between NiCad and LiPo/LiIon.

But when you start talking about drivers and lenses and batteries, I get lost. Don't get me wrong, I could blindly order the parts and put it together, I just wouldn't really know what I was doing.


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## Knight511 (Nov 26, 2010)

http://forums.mtbr.com/lights-diy-do-yourself/very-easy-xm-l-build-805894.html

After a lot of reading and such on this forum, the thread above finally put the period on my learning. As so far as design goes, the sky is the limit. At first, the amount of info hurts the head because not a whole lot of it is sorted out for the VERY beginner.

I am going to Home Depot later to pick up a few things to start my build (finally), but ultimately, I am going to use the Copperhead design linked below for my "influence." Not copying it exactly, but I like the copper tube look, so I am using some of the info here:

Copperhead


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## wmac (Sep 29, 2010)

Okay, we'll, I'm willing to write a Noob guide if you guys are willing to answer these questions:

Why would anyone want to build their own light vs buying?

What are the different types of lights?

What makes a good light?

What makes a good battery? Different types?

What is a good beginner project? What housing, what LED, lense, driver, battery?

What would be a good second light to build?

What would the Mack Daddy of lights look like?

I'll think of other questions as these are answered. Thanks for the help!


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## bikeabuser (Aug 12, 2012)

wmac said:


> Okay, we'll, I'm willing to write a Noob guide if you guys are willing to answer these questions:
> 
> Why would anyone want to build their own light vs buying?


Myself,
I like to tinker, and such things stimulate the mind, while keeping me out of the bars


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## adrenalnjunky (Jul 28, 2007)

Answered in red below:



wmac said:


> Okay, we'll, I'm willing to write a Noob guide if you guys are willing to answer these questions:
> 
> Why would anyone want to build their own light vs buying?
> Same reason anyone does anything themselves instead of having someone else do it. For most of us, this isn't a necessity - we could all go out and buy nice lights, it is a hobby just like frame building, or R/C planes or cars.
> ...


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## wquiles (Aug 22, 2010)

A little bit dated, but probably worth reading:
Introduction to modifying flashlights ...

Will


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## random walk (Jan 12, 2010)

wmac said:


> Okay, we'll, I'm willing to write a Noob guide if you guys are willing to answer these questions:
> 
> - Why would anyone want to build their own light vs buying?
> - What are the different types of lights?
> ...


In addition to this list, the guide could include sections on:

- Electrical principles (relevant to light circuits)
- LED configurations and current/voltage needs (single, multiple in parallel or serial)
- Battery configurations (incl. pack construction)
- Battery charging, protection & maintenance
- Drivers
- Optics
- Housing material and machining
- Thermal control
- Assembly
- Mounting

All of this is covered in detail but is spread around in various threads within this subforum. A one-stop-shop (thread) would be nice.


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## wmac (Sep 29, 2010)

Good stuff Will! I'll take a lot of that information into consideration!


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## wquiles (Aug 22, 2010)

wmac said:


> Good stuff Will! I'll take a lot of that information into consideration!


You are welcome. Please feel free to use/borrow/copy whatever you feel might be useful - we learn by sharing 

Will


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## troutie-mtb (Sep 20, 2007)

Some very good answers given :thumbsup:
and Wills guide is excellent and got some good points in for your Noobs Guide .

However DIY bike lights have changed a heap over the years just as the leds have .
for a truly comprehensive guide you need to decide do you go back to the start of the led revolution or take it up from now .
Be easier to start afresh and probably more helpful to noobs and experienced alike to maybe do a prologue of the early stuff and then a current guide using the popular XP-E / G leds and the XMLs as they are the ones most used at the moment . 

Leds and drivers I see a guide and jargon buster section as its the techie bits that confuse most new builders .

Optics and reflectors must feature in this guide too 

Housings and materials is where the most imagination has been in the past with quite bizarre things getting used in very imaginative ways . its also a stumbling block which puts a lot off as they dont wish to invest in complex tools .

Heat sinking and thermal compounds of course will feature strongly and lots of experiments have been done in this field but it also varies in where you live .
I can get away with a lot less heat management in the UK due to much lower ambient temperatures than say a builder in the warmer climes .

Cables/ connectors/ switches and power entry is another section of importance
as are the Batteries and chargers 

Waterproofing from JB weld / Orings / rubber gaskets / Silicon sealants and probably other methods I have missed .

Next Light and battery mounting solutions of which there are many .

Tools from basic to complex and of course a soldering section would be most helpful

All the above plus what is happening a fair bit now that the mainstream bike light makers have embraced leds it the glut of old lights which still have good batteries that make good hosts for LED upgrades or conversions this is a field which I see getting a bit more popular as the old Hids and halogens die .

And as mentioned in other posts its not now a way to get a cheaper kick ass light as it was a few years ago .its more a hobby for the compulsive tinkerer.

Good luck with your guide and I look forward to seeing it in the future and I think I speak for most on here that we will help all the way if you need tips


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## Ofroad'bent (Jul 10, 2010)

Here's a link to an easy build with the Easy2DIY body
http://forums.mtbr.com/lights-diy-do-yourself/easy2led-xm-l-build-737057.html.

Later builds were done with better optics by reversing the housing and using a deeper back cap.


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## wmac (Sep 29, 2010)

Okay, so the main parts are:

Optics/reflectors, LEDs, drivers, housing/heat sink and battery

Is that correct?


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## wquiles (Aug 22, 2010)

wmac said:


> Okay, so the main parts are:
> 
> Optics/reflectors, LEDs, drivers, housing/heat sink and battery
> 
> Is that correct?


Yes, but "little" things like thermal paste and/or two-part thermal epoxy (which can be re-used for more than one project) are important to have on hand prior to start the project. Also keep in mind that depending on the LED driver, you might need to provide a thermal path from the driver to the heatsink/housing, without shorting the driver to the housing (typically sitting at GND potential). George (TaskLED) often includes a stickie two-sided thermal pad just just this exact purpose 

PTFE wire is also great as it the outer layer does not melt away while soldering - lots of places sell it:
PTFE High Temperature Stranded Wire

Will


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## Ofroad'bent (Jul 10, 2010)

wmac said:


> Okay, so the main parts are:
> 
> Optics/reflectors, LEDs, drivers, housing/heat sink and battery
> 
> Is that correct?


Other things that are important are waterproof cable glands and waterproof switches and connectors, and also the mounting system.
The battery needs a protection circuit of some sort, either included in the cells or mounted in line, and needs to be well waterproofed too with decent connectors and a system for mounting to frame or helmet.

I also include headband and mount in my builds for running/skiing.


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## wmac (Sep 29, 2010)

Here's a first stab at it. I figure I can post this in the beginner section and write another for this section as a follow up that is more detailed and comprehensive about the building process itself.

Riding your bike doesn't have to stop when the sun goes down - get a light! There are a lot of great lights for sale, but some prefer to build their own light*system. Although building your own won't necessarily save you money, there is a sense of pride and satisfaction that comes from building your own light system. Before you can start building your own light, you need to understand the different parts of a light system. A light system can be broken down to: light source, optics, power source and housing.

Most modern lights use an LED instead of an incandescent bulb. LEDs are a specific type of semiconductor, light emitting diodes. The reasons are that they are more durable and use less battery power to emit the same or more light compared to traditional bulbs. Light output is measured in "Lumens." LEDs are designed to handle a specific number of watts, so, an emitter that can handle more watts is one that can potentially output more lumens.









Modern LEDs with an emitter inside a hemispherical lens
Photo by odtexas

Building a light with an LED is a little more complex when compared to a traditional incandescent bulb. Remember doing an experiment with a battery and a light bulb back in science class? It was simple. Touch a positive wire to the bulb and positive pole of the battery and a negative wire to the bulb and negative battery pole and you have light.

Well, that doesn't always work with LEDs because they are directional, meaning, the current only flows one way. They also only operate within a specific current range or else: they will emit light inconsistently, they could get too hot or even burn out immediately. The reason is LEDs are current controlled devices and you must deliver a consistent current to the LEDs over a range of load voltages to maximize their potential. To accomplish this, modern LED lights use "drivers" instead of resistors.









Modern drivers are used to regulate current to LEDs
Photo by odtexas

The reason resistors aren't used is because the current and voltage in resistors are linearly related whereas the current flowing in an LED is an exponential function of voltage across the LED. In other words, a small change in voltage can produce a huge change in current. This is important because you want your light to deliver a consistent beam regardless of battery power. With a resistor, it would only limit the maximum current delivered, but would get exponentially more dim as the battery delivers power.*Therefore,*you need to take the driver into consideration when purchasing the LED because overdriving an LED a little will degrade it substantially.

When buying a driver, it should come with a rating that looks like this:*

- Current: 3000mA
- Voltage: 6-18V
- 3-Modes: high, low, fast strobe
- Designed for XM-LT60 emitters

That means it can deliver a maximum of 3,000 milliamperes with a voltage range between 6 and 18 volts. It also has the ability to deliver a low beam, a high beam and a strobe. Notice it says it is designed for a specific type of emitter? The*rating for that emitter looks like this:

280 lm @ 700mA
1500mA - Energy Star Max Drive Current
3000mA - Max Drive Current
6500K - Color Temperature
Lambertian Radiation Pattern
20mm Diameter PCB

This means it will deliver 280 lumens when supplied with 700 milliamperes of current. It can still operate efficiently at 1,500 milliamperes and should be able to handle 3,000 milliamperes before it burns out. So, why not just run it at 3,000 milliamperes?*In most cases, driving the LED at a higher current will not produce substantial additional light. Instead, the junction (the working parts of the LED) has to dissipate the excess power as heat. Heating the junction will decrease its useful life, and can reduce the output of the LED substantially. Heating it enough will cause catastrophic failure (producing a dark emitting diode).

Some may give a rating in volts, like 5V.*These are really not rated to operate continuously at 5V in most cases. It is better to spec your LED in terms of current, not volts.

The "6,500K - color temperature" is a rating to give an idea of where it is on a scale from how white to how yellow, or more natural (like sunlight), the light appears. This is only a matter of preference.

Most modern LEDs are a square emitter embedded in a hemispherical lens. This configuration will emit the light in a fairly even, hemispherical, 180 degree pattern. For the purposes of riding a bike at night, we want to reform the light into a desired pattern using a reflector and optics, also known as a*collimating system.









Diagram of a collimating system for an LED light system

Collimating systems enable you to focus the light in a specific pattern. They are the combination of the interaction of the lens (the glass bubble over the emitter) and the reflector (the concave, reflective, surface that focuses the light) and optics (any magnification of the beam emitting from the emitter, lens and reflector).*A good collimating system will distribute the light efficiently and evenly with the right amount of throw, hotspot and coma for your application.*

The distance the light travels is often referred to as "throw." (For you math nerds, throw is the luminious intensity calculated as the square of luminous intensity divided by .25.)*When you shine a light on a wall, the inner most point should be the brightest spot, known as "the hotspot." The diffused, "soft," light emitting outward from the hot spot is often referred to as "coma," while the light that is lost outside the coma due to diffusion is called the "spill."*

The amount of throw, coma and spill will be determined by the intensity of the emitter and the configuration of the collimating system. *Changing the throw, hotspot and coma is quite simple. To *increase throw, choose an emitter with higher luminance and/or increase the diameter of the collimating system. The depth of the reflector will determine the size of the hotspot and coma. When comparing two reflectors of the same diameter, a deeper reflector has a smaller hotspot and larger coma. Conversely, a shallow reflector has a larger hotspot and a smaller coma.

Reflectors come in various levels of quality. Higher quality reflectors are coated in materials that reflect the light more efficiently. Efficiency is measured in terms of how much light is absorbed into the reflector instead of being emitted forward into the beam. At the bottom of the quality spectrum are aluminum coated reflectors with 70%-80% efficiency. Next are silver coated reflectors with 90%-95% efficiency and at the top are the dielectric coated reflectors with 99%+ efficiency.

Some reflectors are smooth on the inside and others are rippled. A smooth reflector has more throw than rippled one, but, ripple reflectors have a more uniform beam.

The final piece of the collimating system is the protective lens. This is usually a flat piece of plastic or glass that can sometimes have a magnification "bubble" above the LED. This is usually designed to help maximize luminescence and minimize spill.

The next consideration is a power source. The important factors in choosing a battery pack are milliamperes per hour and volts.*Milliamps Hour (mAh) is important because it's the easiest way to distinguish the strength or capacity of a battery. The higher the mAh, the longer the battery will last. Batteries with different mAh ratings are interchangeable. If your battery is rechargeable then the mAh rating is how long the battery will last per charge.

Milliamps Hour is 1/1000th of a Amp Hour, so a 1000mAh = 1.0Ah

Think of a car. Voltage is how much power is being output by the gas and mAh is the size of the gas tank. *The bigger the gas tank (mAh) rating the longer the device will run. If your battery is rechargeable, then think of the gas tank as refillable (rechargeable).

Most modern light systems use Lithium Ion batteries, the same battery technology used in personal computers. They are typically rated something like, 2,500 mAh/3.7V. This means it will output a maximum of 3.7 volts for 2,500 milliamperes hours. The voltage of this battery will drop as the power is being consumed, so, that means the battery power is not linear. If you look closely at the spec sheet, it will say something like: "The voltage of full charge and cut-off discharge is 4.2V and 2.75V."

This is exactly why we use a driver, because, without it, we would have a really bright light at full charge and a really dim light as it nears full discharge. However, using the example driver above, it requires at least 6 volts. In order to increase the voltage of the battery pack, you would put the batteries in a "series" and it means exactly like it sounds. You would line them up positive pole to negative pole. Two batteries would yield *2,500 mAh/7.4 volts (actually it would be 8.4 at full charge). Three batteries would yield *2,500 mAh/11.1 volts (12.6V) and four batteries would give *2,500 mAh/14.8V (16.8V).

Notice the mAh did not change. If you put them in parallel, a different way of wiring them, two batteries would yield 5,000 mAh/3.7V, three would yield 7,500/3.7 mAh, and four would give 10,000/3.7 mAh.

For our use, we would want to put four batteries in a series.*If you don't want a long skinny battery, you can turn them sideways and wire them into a rectangular battery pack, or, any number of configurations to make them fit your housing.

Which brings us to the final section - housing. Without it, you would just have a bunch of stuff flopping around. When constructing the housing, you need to remember lights create heat and you need a way to dissipate the heat. A lot of light systems use "fins" to increase the surface area of the housing to allow the air to touch more places and cool the housing more efficiently. You can also minimize the heat by under-driving your LED or using multiple, smaller, LEDs.

With this information, you should be able to venture into the numerous DIY light threads and at least have an understanding of a light system and how the components work together and why. Now, venture over to the DIY Lights Forum and see if there's a project you'd like to give a try. Good luck!


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## Vancbiker (May 25, 2005)

Holy spit! Either you love to type or are a masochist! 

If this does cut down on the number of "newb advice" posts, I'll be pleasantly surprised. It is too easy to throw out such a request and field the replies than to do ones own research. Good job though and let's hope that it becomes well used.


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## Toaster79 (Apr 5, 2010)

This should be a sticky. We'd avoid too many questions with all the answers in one thread.


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## wmac (Sep 29, 2010)

Any inaccuracies or necessary changes?


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## wquiles (Aug 22, 2010)

It is a great start, and it will only get better and better as more details are added over time - good job :thumbsup:

To me a few things that are important to know/learn that in my humble opinion (my 2 cents worth) "should" be part of this guide:
- It should be noted more strongly that LED's are current driven devices - you vary the output of the LED by adjusting the current going into the LED, "not" the voltage. The vast majority of power supplies and regulators are voltage regulators, which adjust the output current in order to maintain the output voltage constant. For LED's we need a current regulated circuit: it will adjust the output voltage up/down in order to maintain a constant output current.

- LED's are a lot more efficient at lower currents, and the life expectancy is also significantly longer at the lower current ranges. If the LED is "rated" for 1.5Amps, and you can get adequate output/lumens/covarage/whatever at 1.0Amps, the LED will be more efficient and your runtimes will be longer at the lower current level.

- It is very important for longevity to have proper heatsinking of the LED driver and the LED itself, and the fact that the housing/heatsink size needs to be fairly proportional to the total watts being dissipated. You can't put 3x XM-L's at 3amps in a very small housing, and expect them to last - they will self-cook to death, exactly the same way a CPU Microprocessor in a PC would die if it did not have adequate heatsinking and/or airflow. The key to remember here is that although it is true that LED's are "efficient", most of the power that goes into an LED turns into heat (80-90%) so this thermal energy has to be dissipated properly, as the lumen output of the LED decreases as its temperature increases.

- LED driver efficiency. Many of the low-cost LED drivers have very poor efficiency - you could be wasting 1/4 to 1/3 of your battery power capacity as heat within the LED driver, meaning your runtimes will be shorter, and the housing/enclosure will get hotter than necessary, which will in turn affect the life expectancy of the LED itself. Unfortunately you need two voltage measurements and two current measurements (simultaneously) to properly measure driver efficiency, which is why most/all LED drivers don't even quote efficiency - worst, they might quote the highest/theoretical value, leading you to believe that the driver is efficient thought their input voltage range. For these low efficiency drivers, typically, the larger the difference between the input voltage (at the battery) and the sum of the vf's (at the LED's), the worst the efficiency becomes. If your runtimes seem significantly shorter than your theoretical values based on measured battery/cell capacity, the LED driver is usually the one to blame.

- Besides the lumens/watt output of an LED, and its color temperature (like 6000K or 4500K), another "very" important parameter in terms of color accuracy is the CRI rating. Right now, it is the oppinion of most folks who have tried/used it, that the Nichia 219 with its 4500K and 92 CRI is one of the most accurate/color rendition LED's available today. BUT, this color accuracy comes at the cost of slightly lower efficiency - less lumens per input watt, compared to most "bluish" white LED's in the 6000K range (which might have a much lower CRI).

Will


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## wmac (Sep 29, 2010)

Thanks Will! I'll work it into the one above over the next couple of days. I posted the version above in the Beginner section to drive some traffic over here. Too bad we don't have a wiki


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## yetibetty (Dec 24, 2007)

wmac said:


> Any inaccuracies or necessary changes?


It might be an idea to explain the three main types of driver (buck, boost & linear) as it's a constantly asked noooob question. Oh and the bit of extra battery voltage over LED forward voltage required for buck and a bit less battery voltage than LED forward voltage required for boost etc.

Don't forget to explain what forward voltage is too

Good write up BTW keep it up.


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## wmac (Sep 29, 2010)

yetibetty said:


> It might be an idea to explain the three main types of driver (buck, boost & linear) as it's a constantly asked noooob question. Oh and the bit of extra battery voltage over LED forward voltage required for buck and a bit less battery voltage than LED forward voltage required for boost etc.
> 
> Don't forget to explain what forward voltage is too
> 
> Good write up BTW keep it up.


Thanks! I knew almost none of that stuff before last night and your suggestion is new to me. Any threads that already explain it?


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## yetibetty (Dec 24, 2007)

That's the problem, there are bits and pieces on the subject all over the forum. I'll have a search and see what I can find.


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## mattthemuppet (Jul 16, 2004)

easiest rule of thumb for number of cells is:

buck driver - no. of LEDs + 1

boost driver - no. of LEDs - 1

pretty simple


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## wmac (Sep 29, 2010)

Oh, quick research shows that you'd use a buck driver if your battery pack's voltage is higher than rated and boost driver is opposite, correct?

So, in my example, a 4-cell pack in series would yield 16.8V at max charge and the driver is rated for 6-18V. What type of driver would be appropriate?


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## mattthemuppet (Jul 16, 2004)

it's the relationship between the voltage (Vf) of the LED string and the voltage (Vin) of the battery. For a buck driver Vin>Vf and a boost driver Vin<Vf.

So the battery voltage does not dictate the driver, the no. of LEDs (and how they're wired) and the battery voltage together do.

Using your example, a 4 cell pack would happily drive a 3 series LED string using a buck driver or a 5+ series LED string using a boost driver. The voltage range of the driver merely states the voltage range within which it can work, not whether it's buck or boost or how many LEDs a given battery within that range it can drive.

Just use the rule of thumb I posted above, honest, it's really that simple. If you want to run a 2 series LED light, then you either need a 3 series cell battery and a buck driver (most likely) or a 1 series cell battery and a boost driver. If you use a buck driver it must be able to accept a Vin of up to 12.6V. If a boost driver then it will have to go down to 3V.


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## wmac (Sep 29, 2010)

Thank you for all your knowledge and patience! Yetibetty gave me access to a pic and it explains they why behind what you are saying. It seems to me that a goal of a good lighting system is to minimize heat. Using a several cell series to create high voltage in tandem with a buck driver seems like the best scenario, right?

It makes sense that you can't always get this scenario with a multiple light set up, so, a boost driver is required.


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## troutie-mtb (Sep 20, 2007)

There is a bit of a hiccup in that diagram now that XMLs are coming in at about 3 volts VF 
making is easily possible to drive 4 XMLs from a 4 cell battery pack and a Buck driver .


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## yetibetty (Dec 24, 2007)

troutie-mtb said:


> There is a bit of a hiccup in that diagram now that XMLs are coming in at about 3 volts VF
> making is easily possible to drive 4 XMLs from a 4 cell battery pack and a Buck driver .


There is more than a hiccup I wasn't expecting it to appear on here. All numbers are very approx and as usual I'm out of date


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## wmac (Sep 29, 2010)

Pic removed.


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## yetibetty (Dec 24, 2007)

You can put it back I don't mind at all. I would have spent a little more time on it if I knew it was for world wide viewing, that's all. If it's not back soon I'll sulk


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## georges80 (Jan 5, 2010)

If you want to pull some info on buck/boost linear drivers etc (direct cut/paste is fine) feel free to use my faq as a resource:

Frequently Asked Questions

cheers,
george.


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## wmac (Sep 29, 2010)

It's back Yeti. Thanks George!


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## wmac (Sep 29, 2010)

Anyone still making their own lights?


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## Vancbiker (May 25, 2005)

I have some plans bouncing around in my head for another helmet light, but nothing started yet.


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## ilium007 (Mar 31, 2015)

wmac said:


> Anyone still making their own lights?


I'm researching at the moment. I am thinking a 2 x XM-L2 light for bars and a single for helmet. Looking at easy2led housings but not sure yet.


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## scar (Jun 2, 2005)

ilium007 said:


> I'm researching at the moment. I am thinking a 2 x XM-L2 light for bars and a single for helmet. Looking at easy2led housings but not sure yet.


Yep :thumbsup:

****


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