DIY LED Lamp project

[Rikki]

Idea:

[_gl]

Thanks for posting these Rikki, I might try one one of their bulbs. I've just been looking at the traditional lights (VL3,7,35 etc), but the LEDs will last far longer, won't get hot, plus you don't need to buy expensive replacement bulbs. The output seems pretty good too (at that level of lighting).

I think I would buy the colder lights though, that 2700-3000k seems too warm - if you're not concerned about matching other lighting, a colder light will give you a better colour balance, ie. more to work with in post.

I'm also looking at the 3W luxeon 12V bulbs, but haven't found any pictures of their spread or hotspotting - anybody familiar with these?

Another idea was to buy a cheap traditional light for the hotshoe, and powering LEDs off it. Shame those bulbs are only available in 12V - but you could wire an LED matrix easily enough. Anybody have recommendations for good LEDs for that?

[_gl]

I think I would buy the colder lights though, that 2700-3000k seems too warm - if you're not concerned about matching other lighting, a colder light will give you a better colour balance, ie. more to work with in post.

For example, their non-warm version is listed as 6000-6400k, that's a very close match to the 6500k used for PC monitors & TVs.

[_gl]

... while I'm brainstorming on this, isn't there a problem with running two lithiums? From memory (and I may be wrong), without any control circuitry, one battery will drain before the other, and may drain below it's safe threshold, leaving it unchargeable. Although it would be nice if it worked...

[jackhughes]

Im really intrested in a DIY LED light too,
I was thinking of powering the LEDs by a battery pack (something that can be mounted to a shoulder rig mount, or a belt pack).
Maybe a drill battery and use a buck converter to get the right voltage.
Also include a variable resistor to dim it.

Im an electrician so wiring this would be easy.

Im mostly worried about the size and design.
I want to mount it to a bracket like Taky'shttp://www.hv20.com/showthread.php?t=1401
Run the wires along the bracket and use some connectors.

Also, if i want to film a wedding reception, what is the color/temp that i should use?

If someone tells me which LED set/temp i should get, i could finish it in a weekend. (except for the housing)
Hopefully the LEDs cost less than $10 and battery cost less than $30

[mattias]

without any control circuitry, one battery will drain before the other, and may drain below it's safe threshold, leaving it unchargeable

actually a led, like any diode, is a control circuitry. once the voltage drops below a threshold the current stops. i don't know if this is enough to protect the battery though, i'm not sure how they work specifically.


/matt

[RicanJoe]

Yah. Uh Huh! "- Cyan (or Green) high power/high efficiency LED's"
Not for me thanks!

Use gels?

[_gl]

Use gels?

Won't work - if the light was only lightly cyan-tinted you could compensate, but LEDs produce strong colours.

[_gl]

Did you do any more work on this Rikki?

I'm still tending towards powering from the hot shoe for convenience & one-handed operation, which rules out the 12V bulbs... but no sign of a cheap VL-3 to hack so far.

Powering off the HV20 lions would be great if it worked too, and would allow you to draw more juice - but wouldn't it be tricky to connect the contacts in a removable way? Nimh AAs would be OK too (but I wouldn't want to use 10 to power a 12V!).

I was originally thinking about wiring a 20,000mcd 5mm LED matrix. This Ebay seller can supply ~3000Ks and ~5000Ks (the 5000s are what you get from the listing). You could intermingle them and dial in a temp with two pots. It's a lot of wiring though.

A pre-wired alternative I've just looked at are these 100 LED flashlights on Ebay:



There's a YouTube video of one in action here. You wouldn't have colour temp control (except with lossy gels), but two of those side-by-side would give a decent spread.

Or for max. power (but probably not as even a spread), how about a 3 Cree 7090 XR-E 500 lumen torch?



Could be diffused I guess.

[_gl]

Actually these 10mm LEDs are mind-blowingly bright: 140,000 mcd/25deg @ just 20ma ! According to this calculator that's an incredible 20.85 lumens.

A 50 LED panel would produce ~1043 lumens and draw only 1amp @ 3.6V. That's 2+ hours runtime for every 3 NimH AAs. You could probably run more than half direct from the hot shoe.

(I also spotted these 255K mcd ones, but they run at 100ma (made up of 5 chips), so are in effect only 51K mcd per 20ma).


Edit: The mcd rating is meaningless without the angle of the beam, the 100ma's are of similar brightness when you take it into account.

[mattias]

they are most likely mind blowingly blue as well, and don't believe the no heat argument too easily. many leds need to be attached to a heat sink to work well. they don't radiate so much heat but the led itself gets really really hot.

/matt

[_gl]

they are most likely mind blowingly blue as well

Probably (I'm waiting on their colour temp.) - especially when driven at their max. rated 3.6V. But you could mix them with their warm 85K mcd ones.

and don't believe the no heat argument too easily. many leds need to be attached to a heat sink to work well. they don't radiate so much heat but the led itself gets really really hot.

Yes, I expect those puppies do get warm - but as they're standard plastic packages, I wouldn't expect them to need heatsinks... although in a matrix, and with some kind of plastic cover, it could be a problem (EDIT: it's not, they only get warm to the touch at full blast).

[Tõnis]

I have tried that 3 Cree led MR11 bulb and first it gets really hot but is enclosed so it will not burn you secondly it has a really narrow and not diffuseable angle. Also warm Crees are still quite cold.
But if anyone needs to neatly power MR11 or MR16 led bulbs that 12V lithium ion battery and charger from the ebay will run those at least for three hours and that`s for $15 incl shipping.

T

[_gl]

I have tried that 3 Cree led MR11 bulb and first it gets really hot but is enclosed so it will not burn you secondly it has a really narrow and not diffuseable angle.

Isn't it usually the reflectors that narrow their output? I've seen quite a few Cree style ones with wide angles.

But if anyone needs to neatly power MR11 or MR16 led bulbs that 12V lithium ion battery and charger from the ebay will run those at least for three hours and that`s for $15 incl shipping.

That's another option, do you have a link? (I can only find ones at double the price).

You could use them with this single 900 lumen LED - 130deg angle, 900ma @ 12V, 6500k. Less hassle than wiring a matrix, but needs a heatsink & driver (or some way to limit current) & around twice as expensive as a similar matrix with the 10mm's... and no colour temp. control.

[_gl]

After more research, I've decided against the single 6500k 890lm light (driver circuitry too complex for my limited electronics skills & fixed colour temp), or the 144kmcd lights (beam too narrow, too much wiring).

Instead I've ordered wider-angle LEDs in 210kmcd warm (100ma 40deg), 95kmcd warm (20ma 60deg) and 280kmcd normal (100ma 40deg) (which looks pretty blue in the pic). Much fewer required, good spread, and colour temp. can be dialed in to suit.

[_gl]

[RicanJoe]

Its seems like you mixed color temperatures. Did you? So far so good.

[_gl]

Its seems like you mixed color temperatures. Did you?

Yeah, it's a mixture of all 3 LEDs I bought (post #40). It's incredibly bright, a little less so now that I've added a diffuser, but the light is smoother for it.

The LEDs are drawing 2amps worth of juice from 8 rechargeable 2100ma AA batteries (Hybrios). Lasts about 2 hours at full brightness. I'll post a comparison with the HV20 built-in light in darkness when I get time, here's another pic (pre-diffuser):



(it's blindingly bright on full *actually even at the lowest setting *, this was exposed at the lowest to show the LEDs).

BTW, as you can see in the pic the cooler whites aren't blue, but neutral. Many LED sellers on Ebay call 6400K 'neutral', that's probably what these are.

[Rikki]

Just read through this thread again.

Sorry for the delay.

I disappeared for a few months in Feb and march hence no response then but now back and still interested in pursuing this avenue.

I found this new Sima product - http://www.thetwistergroup.com/produ...%20D41007.html - but am not impressed as it uses a bespoke 3.7v Li-ion pack built in that you cant remove. If it was 3x AA's you could pop in life would be far sweeter. Also not sure on the output power or colour balance.

[Rikki]

Just disassembled the LED unit I got in January and was wondering if anyone with any electronics know how could tell me if it would be easy/possible to make the unit work on 6v instead of the 12v it runs on just now.

It fits the Jessops lamp I have here perfectly size wise so just need a way of dropping it to accept 6v and it should be an easy install.

[_gl]

As promised, here's a video of my (now diffused) LED light vs the HV20 built-in LED. I was approx 2.5m from the wall, exposure was locked on the HV20 light.

Here's the final version with the diffuser, mounted on a camera clamp. The diffuser is just a piece of flexible clear plastic (actually a part cut from a rectangular Asda cotton-bud container that happened to fit perfectly) roughed up with fine sand paper. Unfortunately it does loose some brightness with it on, but it really smoothes out the light:



Without diffuser:

[_gl]

Just disassembled the LED unit I got in January and was wondering if anyone with any electronics know how could tell me if it would be easy/possible to make the unit work on 6v instead of the 12v it runs on just now.

One solution is to find a 'boost' power converter/switch. This is an electronics part which can boost a lower voltage to a higher one (there are also 'buck' converters that work the other way). I've never used them though so I can't help with details.

You might also be able to modify the circuit driving the LEDs, if it's dropping the voltage. But if they drop the voltage (to the ~3.4V that white LEDs usually need) by connecting several of them in series directly on the board, then you'd have to modify it which may be tricky.

EDIT: Looking more closely at the board, it seems that 3 LEDs are connected in series, so that's 12V / 3 = 4V per LED. That's a bit high, but the driving circuit probably drops the voltage a bit, likely closer to 3.6-3.8V per LED (which is reasonable for whites). You can't easily change that without a lot of board hacking IMO, so try the boost converter.

[Rikki]

Right well today I made some progress too fella

I decided to test the voltage going from the PCB to the LED array and it was putting out 9.4v DC. So I am now thinking that the top PCB is just some kind of DC control and step down circuit (as it would take 12v DC with any polarity you threw at it and stepped it from 12VDC to 9.4VDC).

Ive now ripped the PCB off and binned it so only need to power the main LED array with 9.4v or 7 x AA rechargeable cells (rated at 1.2 but really 1.4v).

My hack is now almost complete, all I need to do is head in to Maplins tomorrow, pick up some AA battery holders and a variable pot so I can control brightness too.

Which one did you end up buying as Ill probably need something similar.

Once I've finished all that then I'll build it up, make a video guide to it all and see how it performs

[mattias]

the voltage over 3 leds will always be three times the led voltage, which is constant. the rest of the voltage ends up over any resistors in the circuit and becomes heat. a led driver controls the current flowing through the leds, not the voltage, which again is always constant.

/matt

[_gl]

My hack is now almost complete, all I need to do is head in to Maplins tomorrow, pick up some AA battery holders and a variable pot so I can control brightness too.

Which one did you end up buying as Ill probably need something similar.

I bought a pot with rotary switch, expensive but worth it for me, single control for everything.

BTW, what I didn't mention is that my light is actually software controlled, that will eventually allow me variable colour temp & special effects (strobing, flame flicker simulation etc), but that will have to wait till after my upcoming shoot.