Road Train !!!!!!!!!!

by Russell McMahon

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I met a friend of a friend last night who used to be a pro photographer. He had this gimmick that he said was kinda home-made by some shop owner in Singapore. I wish I took a pic of it, but I forgot. I will try to explain as best as possible.

It was basically a super bright LED, usually used for floor lighting or some such, housed in a tiny box that's about 1 inch × 0.5 inch × 0.5 inch, powered by either AA or AAA batteries, with an on-off switch, and most importantly the LED itself is diffused by a small square plate of I-don't-know-what material. Continuous lighting that's extremely portable, can fit three of them in one palm, and runs a couple hours on batteries. Is there any product like this sold anywhere, online or otherwise?

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1  
Super bright, small, and multi-hour battery life: pick two. –  Evan Krall Jul 30 '11 at 5:29
1  
ok super bright and small please :) thank you –  rabbid Jul 30 '11 at 5:52

4 Answers 4

up vote 4 down vote accepted

At that size it would probably be using a CR123 type battery. Two of them in series will light up extremely bright LEDs. Ones you can get like a surefire type body will last about 20 hours on a pair of those but are only bright enough for "seeing" and won't light up a small room for photography.

Of course you can go nuts with with a diy led driver that pushes an led module with more than 5 watts. Taking a glass plate and grinding into a makeshift lens and sandblasting will give you a diffused refractor that you can reverse for wide or narrow beam in it's most simple form or you can even make a rail with the lens in a housing so you can "zoom" the light angle. If you only want diffusion then cut out an acrylic piece and sandblast or hand sand it down.

I built something like this for a few different projects, it's not hard if you can source all the parts. A module that's less than 10 bucks can shoot out 300+ lumens which is more than most Surefire weapon lights...

The most economical power supply would be li-ion 18650 sized batteries. They look like AA size but slightly bigger; almost all laptop batteries are composed of a bunch of these stuck together in a slab.


Here's a sample diy light source

you could build- it will provide slightly less than 700 lumens at 6500k color temperature and 70 CRI quality and will probably fit in an enclosure the size of a Rubiks cube. Runtime is 8 hours This is similar to the box you described earlier; it will light up a room with no problem.

for example, this photo shows a flashlight with "only" 500 lumens, so now you know what the device is capable of.

part / description / qty / approx price / source

  • 5 watt led module / with heatsink / two of these / ~ $14 / superbrightleds.com
  • LG 2600mAh li-ion cells / 18650 size / six / ~ $45 / batteryjunction
  • 1.0 ohm 1w resistors / vishay dale or milspec / two / ~ $3 / mouser
  • diffuser / sanded or blasted acrylic, maybe glass / one / ? / hardware store
  • enclosure and switch

here is roughly what it would look like:

link to diagram


There are various ways to adjust the lighting angle and intensity.

Angle

By having the leds inside a can on a "rail" system with a parabolic reflector, you can adjust between a wide angle light or a spot light.

this photo shows what I'm talking about.

Light Intensity

There are three ways to adjust light intensity:

  1. Use paper gobo or something = waste of power, easy, free, lower intensity

  2. A switch to halve the voltage = more wiring, 7v led may not be efficient at 3.6v, lower intensity

  3. Have four 5w leds instead of two, wired to turn on 1 or 2 or 4 at a time = jungle of wires, efficient you get three intensity settings:

    • 350 lumens@ 20 hours

    • 700 lumens@ 8 hours

    • 1400 lumens@ 3.2 hours

Obviously the third is the best. It isn't very expensive because you are only adding two more leds; most of the money is in the battery and charger. Labor is another story :P


Recharge the batteries; CAUTION

You'll note that I haven't mentioned how to recharge the batteries. It depends on whether you want to use an external charger with battery slots to charge each 7.2v pair (very tedious) or will be keeping the batteries inside(convenient and safe) and using a "battery pack charger"(like a normal charger but doesn't hold batteries, it has wires instead that you have to lead to something to charge.)

Either way each pair of batteries will need a protection device attached to prevent dangerous overcharging and a damaging over-discharge when low on juice.

The safest way to charge the system would be like this

Wall -> this charger, set to 8.4v -> the light system's three jacks -> each jack to the respective battery pair's protection board

You need three dc jacks unless which is safest method, using switches or other random ways to save on wiring may result in explosion.


The whole kit with three power settings and best charging method will cost $100 ~ $150+ including random stuff like wires, enclosure and switches.


a word on safety

This whole contraption may explode if you are not not careful, or even randomly. The 15" MacBook Pro also has six cells and it runs for 7 hours so you can sort-of imagine how big the explosion will be, lol.

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1  
Its not a problem with your design or anything, but thats a 100-150 dollars for light output thats a little less than your average inside house bulb. –  rfusca Jul 30 '11 at 15:52
    
Incredible answer! Although the price is a bit high... but this gives me a lot to think about. Thanks! –  rabbid Aug 1 '11 at 0:58
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There are reasonable-quality Chinese manual flashes on eBay for $40 and TTL flashes for a little under $100 - I find it hard to believe this DYI LED flashlight has any advantage over 2-3 real camera flashes (or for that matter over big store-bought LED flashlights in the $10-$20 price range) –  Nir Aug 1 '11 at 14:41
    
@Nir manual flashes aren't CONTINUOUS. Store bought LEDS don't even come remotely close to the power this gives. –  sauceboat Aug 1 '11 at 15:04
    
@rfusca housebulbs use ac power, are at least five times more wattage, have low CRI, unless you get halogen or special coated incandescents and then both of those use more power than anyone can carry in battery form- most of that being wasted as heat. The majority of the cost comes from the lithium ion battery and charging system- with redundant protection on the batteries. Li-ion's discharge is almost flat and is double the voltage per volume/ half the weight vs ni-mh(which aren't cheap anyway). The only other alternative is 3v lithium- except they don't recharge and are expensive.. –  sauceboat Aug 1 '11 at 15:12

This sounds like something that would get way too hot to be sold as a consumer product, all kinds of liability issues (wait until eventually the heat ruptures the batteries, good times).

But it's also the case that simply wiring an LED into a box with a power switch is about the simplest possibly kind of electronic project that could be undertaken. It seems like it would be easy to craft yourself.

Respect the level of heat a powerful LED gives off though, not to mention that the really bright ones can physically damage your eyes if you look at them (hence the diffusers I imagine). You may even want to use welders goggles if experimenting....

And consider keeping the batteries in a separate detachable pack for quick disconnect if things go south.

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Thanks for your reply. I could probably connect an LED to batteries just fine. I know nothing about making a plastic casing though. Where would I even begin on that? Also, I might need some physics lesson, but why would the heat rupture the batteries? –  rabbid Jul 30 '11 at 7:11
    
The heat could rupture the batteries because any tube filled with different materials will expand when heated, and since a battery is sealed... BOOM. Not that it would be a large explosion, but it would be a mess with many small very hot bits and some acid. Also, I would never ever put that in a plastic housing of any sort, ever. Metal all the way. –  Kendall Helmstetter Gelner Jul 30 '11 at 21:29

You haven't said exactly what you're planning to do with this, but it sounds like a flashlight might fit the bill. LED flashlights range from super cheap to super bright, but unfortunately you're not going to get both in one package.

As always when it comes to light, there's a Strobist post about some pocketable/camera-baggable options: your cell phone, and Rosco LitePads, a flat LED panel driven by an external 12v DC power source.

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You could look into normal LED torches, I have an ITP A3 EOS torch that I keep on my keyring, it's only a little larger than the AAA battery it contains. They claim 55 minutes of light on the brightest setting of 80 lumens, and 4 hours at 18 lumens. There is a large range of different torches from different manufacturers giving different trade offs in terms of brightness, battery life, and size. Given that the electronics required are fairly simple I would imagine that they are all pretty similar in terms of efficiency turning battery power into light.

I haven't tried using it for photography, but on the 80 lumen setting it's bright enough that you don't want to look straight at it.

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