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Thread: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

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    Flashaholic jeffosborne's Avatar
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    Default Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    For a while now I have been using neutral-white Rebel LEDs to build small portable lights to use for photography. They tend to be used for table top photography or as fill-in lights for existing lighting, with 500 to 1000 lumen output. When the new high-CRI Rebel emitters became available recently, I was inspired to build a light bright enough to use with a diffuser or umbrella as a primary studio light. I made use of a suggestion made by CPF forum member JTR1962 to add cyan and red emitters to increase the CRI. Thanks, JTR1962!

    This new light uses 15 of the Rebel high-CRI (color rendition index) emitters, part LXM3-PW51, which have a typical CRI of 85. It also has two red and one cyan emitter to further boost the CRI. A toggle switch on top of the light sets the output to either 15 white emitters only, or 12 white with 2 red and one cyan emitter. I wanted to compare the difference that the color LEDs would render. The top panel includes a power on-off switch, rotary brightness dial, and four 3mm indicator LEDs: yellow power on, blue fan on, red battery low, and red overheat. The all-aluminum enclosure is 4.5” long, 2.5” wide, and 2.625” tall, less the feet and handle. It weighs 1.1 pounds. A lexan window covers and protects the emitters. All are hand made with simple tools. I did get a bench top drill press for Christmas last year (thanks Jim!) and that has improved my results over using a hand drill.

    In all-white mode the lamp produces 2500 lumens at the emitters, according to the manufacturer’s specs. With 12 white, 2 red, and 1 cyan, that drops to about 2250 lumens. I do not notice the brightness difference, and the color shift is slight but noticeable. The cyan and red LEDs are driven at 500ma maximum, all the others are driven at 850ma at full brightness. The light contains no batteries. It has a 6’ power cord that plugs into either a battery pack or 12 volt DC power supply. At full brightness it draws 4 amps. The output is continuously variable with the potentiometer, but I tend to use it on full.

    Both side panels have openings that allow air to exit when the fan is on. You can see the sides of the P4 heat sink fins there. The rear panel has several vent holes, and 3 small tapped holes used to mount the driver printed circuit board inside.

    The bottom and top panels also have vent holes for incoming air. The hole near the bottom center has a threaded ¼” female light-stand fitting inside. My primary use of this light has been on a light stand, with a reflector attached. The clear rubber feet are 3M self-adhesive bumpers.

    The emitters are wired as six sets of three in series. The cyan and red emitters are at the bottom row.

    The first reflector I used with the light was an 18x18” sheet of textured Epson Heavyweight Matte paper mounted to foam core board. It made a pleasing soft light, but was not too efficient

    Next I tried a light weight 48” umbrella reflector made by Paul C. Buff Co. with very good results.

    Here’s a portrait made with only the high-CRI light. The shadows are very soft, and the skin tones look natural. The light is set to include the red and cyan emitters for this shot.

    Building the light was fun, and a challenge. With about 40 watts to dissipate, I decided to use a large CPU heat sink and a 50mm, 12 volt cooling fan. Light-stand mounting is a must for studio lights, so a round aluminum adapter with the proper fitting is secured to the bottom. It is next to the fan below. My on-off switch and dimming potentiometer would need to be accommodated, as well as the control electronics, fuse holder, and some wiring. The handle was left over from a previous project, and it is included to keep the top side controls from being inadvertently reset. The plan is to use a ¼” thick aluminum rear panel, cut to the same dimensions as the heat sink, so I can drill and tap holes in each to mount the side panels.

    This is 30-06 aluminum, recommended by the salesman at the local sheet metal shop. Not too soft, but not too brittle either. It was easy to work with. I used 1/16” thick pieces for the side panels, and 1/8” thick pieces for the top and bottom panels.

    The heavier 1/8” thick pieces at the top and bottom help to make a sturdy enclosure. Once the holes are located and marked, I like to use a center punch to keep my drilling on track. Lots of filing is required after the pieces are cut and drilled, to smooth edges and adjust dimensions.

    The large heat sink and rear panel are drilled and tapped to accept #4-40 screws, which secure the top, bottom, and side panels.

    I use a grit impregnated nylon brush on my hand drill to smooth and finish the pieces. Here are all the enclosure pieces, which have been washed to remove any aluminum dust.

    The bottom panel has 5 MOSFET transistors mounted with arctic alumina epoxy. Each transistor is part of a circuit driving 3 LEDs in series. The round aluminum piece in the center is the light-stand fitting.

    The LEDs are mounted directly to the heat sink with thermal epoxy. Near to the center a 50K ohm thermistor is also mounted. When the temperature reaches 140 degrees, the cooling fan comes on. If the thermistor reaches 210 degrees, the control circuitry shuts off the lights. If the fan were to fail this would protect the LEDs from overheating. The threaded spacers mounted to the corners are used to secure the lexan window.

    Oh, I know it looks like a lot of wires, but it is all manageable. The 6 white wires with red ends will all be cut as short as possible and connected to one fat 16 gauge wire that connects directly to the power on-off switch. The other white wires attach to either the toggle switch or one of the transistors below. The braided wire set is the thermistor leads.

    With additional assembly completed, we still have lots of wires. We added wires from the indicator LEDs and the potentiometer, and now all of these conductors will attach to the control PC board.

    The control circuitry resides on a small piece of prototyping board with plated through holes at .1” spacing. The board slides into two nylon fittings at one end, and is secured with a single screw into a threaded spacer at the other end. This arrangement makes it easy to get to the PC board - I need only to remove one side panel and one screw to slide it out.

    Laying out and soldering the components to the PC board is made easier by having the schematic for the circuit drawn around a physical layout of the two comparator ICs. These quad comparators ICs are LM239N.

    Five of the eight comparators are used for the linear current regulators driving the LEDs. Two comparators are used with the thermistor to turn on the fan as needed, and shut the light off if overheated. And one comparator looks at the incoming supply voltage and lights the ‘low battery’ indicator if it drops below 10 volts. My previous lights have used a small signal transistor across the sense resistor to regulate the MOSFET, which requires a .5 volt drop across the sense resistor – not very efficient. Here the small signal transistor is replaced with a comparator, so my sense resistor can be very low ohm - .05 ohm 1% is used. The voltage drop across this resistor is only .045 volts with the maximum 850ma current flow – much more efficient. The blue components at the top are trim potentiometers for the adjustment of low voltage, fan on, and overheat detection.

    This is the completed unit with one side panel removed. The enclosure size worked out well for the space required. After making initial adjustments, it has worked without a hitch.

    The quality of light is improved over my other standard neutral-white lights, for most subjects. I really notice the skin tones, lips, and any warm or brown tone to be improved. This has been a worthwhile project!

    Before I built the light, I knew I would need a larger battery pack for portable use, so I built one in a Bud Industries NEMA rated, waterproof transparent enclosure, with nine 18650 Li-Ion calls in a 3S-3P configuration. It powers the new light for almost 2 hours on full brightness.

    This pack has 3 switched battery outputs and two variable regulated outputs for 0 to 850ma. I will post this project separately in the batteries section of the forum.

    Keep your batteries charged!
    Jeff O.


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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Holy crap!

    Excellent work, I can't imagine how much time you've put into this one & your others. I always enjoy your extraordinary extreme builds. Hope to see more.
    -Will-

    Sorry, I have retired from flashlight modding & I do not make custom flashlights. Thank you for your understanding.

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    super nice and clean build!
    My lightsWTB: Surefire: New/Used/Rare. Currently looking for everything Crosshairs + D2. Interesting trades available.Everybody, just send your lights directly to James - he'll end up with them anyhow, lol. -Kestrel

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Very well done!

    Nice and clean, you should be very proud of it.
    Finning does help dissipate heat. This is why the fins are removed before cooking fish. Otherwise it will throw off the heat and not reach the proper cooking temperature. --Duglite

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    Flashaholic* Icarus's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jamesmtl514 View Post
    super nice and clean build!
    +1

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    Flashaholic* griff's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    shizzle.........
    Sometimes, when I'm feeling down because nothing seems to be going right, I like to take a home pregnancy test. Then I can say, "Hey, at least I'm not pregnant

  7. #7
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    As soon as I saw the words "High CRI Rebel", I knew who wrote this thread. Nice work Jeff - very nice.

    I was curious if you can enlighten me a bit more on the visual results, for the obvious reason that I am doing a build with the same rebel p/n in a flash light, but haven't tested it as far along as you have.

    One of the criticisms often put on LED lights is that the light is "flat". I am still trying to define this, but suspect it is mostly an attempt to describe that the light lacks broad color spectal distribution. (in other words, a lot of missing spectra in the light).

    It is also possible that it refers to how the light is somehow partially polarized, collimnated, or diffused, but I am not at all sure.

    I was wondering if you could comment or help me visualize a few things:

    a) How do photos actually come out with just the high CRI LEDs vs the additional red and cyan? Would this show up on a monitor, or just with a printed picture?

    b) Any comments on the "flat" aspect, regarding if it is from spectral distribution or is this solved with the umbrella reflector / diffuser?

    c) Are the added colors really for skin tones or do they affect other aspects?

    Thanks for posting about the project. It is such a great photography tool.

    HarryN
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Very nice build. I have a Sherline miniature mill in my garage and your results with a drill press make my best efforts look poor by comparison!

    My only criticism is that you used a polycarbonate lens (polycarbonate is the class of material, Lexan is a trade-name polycarbonate product). Acrylic sheeting offers 95% light transmission compared to UCL (98%). Polycarbonate is less, at about 90%. Acrylic is cheaper, too.

  9. #9

    Christo Pull Hair Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Hi: This was an amazing piece of work!!

    I have a queton for you and the rest of the forumn: I am looking for a small LED light for a portable Tabletop studio thta will be used for taking high resolution photos of coins. I would wnat the lights to have a High CRI of >90 and color temperature of 5500 - 5600 Kelvins. I would like for the lights to be fully controlable via computer, just like the camera is going to be.

    I envisoin these lights being on a gooseneck tht will allow flexible placement but rigid enough to support th elighht weights. I would prever to have the power source to be from a centralized UPS/ Battery pack that will be in the transportable case that the table top studionwill be in.

    Any ideas and suggestions would be greatly appreciated.

    Also, i am not a DIYer, so I need to find a commerical product or get very detailed instructions on how to build these lights. I envsion have four of 5 of the lights in the case. One a base/backlight and the other four on each side of the base. The area that the lights would need to cover would be no more that a4" x 4" area.

    Thanks,

    G.E.

  10. #10

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Man, the craftmanship of that light is extraordinary!

    Where did you get your red LED's? I am looking for some to make a night vision light of sorts. Thanks!

  11. #11
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    That is such a great idea, beautifully made! The design is fantastic - it looks so completely professional. I bet you could sell plenty of these to professional studio photographers.
    Resistance is futile...

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Comparators have very high gain, so you really need the capacitor across input and output, as well as a 10uF from +ve battery to earth (-ve).

    Especially if you have open wiring, rather than a Circuit Board.

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    Flashaholic jeffosborne's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Sorry to leave the schematic yet undone, so many things to do it seems.

    Anyway thanks MikeAusC for your insightful observations. I did go over the spec sheet for the LM393 part, and saw that it does have an open-collector output, which is required here. It also operates well with low voltage inputs, which is also needed. So the part should be fine for this regulator. Jason, I wonder about the second comparator on this IC. If it is not being used, you should tie it's inputs to ground, so they are not open to making an oscillator. The output of the unused comparator can remain unconnected. Also, what is the value of the sense resistor you are using? And, do you have the 100K pull-up resistor on the output of the comparator?

    Thanks again for all the encouraging words regarding my light! It is a handy tool. It was used to shoot some baby photos lately, Noah is 6 months old:

    Jeff O.

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jeffosborne View Post
    Sorry to leave the schematic yet undone, so many things to do it seems.

    Anyway thanks MikeAusC for your insightful observations. I did go over the spec sheet for the LM393 part, and saw that it does have an open-collector output, which is required here. It also operates well with low voltage inputs, which is also needed. So the part should be fine for this regulator. Jason, I wonder about the second comparator on this IC. If it is not being used, you should tie it's inputs to ground, so they are not open to making an oscillator. The output of the unused comparator can remain unconnected. Also, what is the value of the sense resistor you are using? And, do you have the 100K pull-up resistor on the output of the comparator?
    Thanks for the advice Jeff and Mike, I rebuilt the circuit again and grounded the two inputs on the second comparator that isn't being used, as well as putting the .001uF cap across the output and - input of the comparator and the 10uF cap across the + and - of the power. Unfortunately the dimming/brightening problem persists, although much less so when touching the led heat sink than before... the pot still has the same amount of it though.

    Below is a drawing I did of how I have the circuit hooked up.. Any thoughts?

  15. #15

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Aside from its functional considerations the unusually high quality of your work has created a device that is very aesthetically pleasing, even beautiful.

    Brightnorm

  16. #16

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jason 77 View Post
    Thanks for the advice Jeff and Mike, I rebuilt the circuit again and grounded the two inputs on the second comparator that isn't being used, as well as putting the .001uF cap across the output and - input of the comparator and the 10uF cap across the + and - of the power. Unfortunately the dimming/brightening problem persists, although much less so when touching the led heat sink than before... the pot still has the same amount of it though.

    Below is a drawing I did of how I have the circuit hooked up.. Any thoughts?
    It would be better to tie one input to ground and one to something else besides ground, that way it stays in the same state. If you have them both the ground, then as the ground potential changes during switching etc... it can cause the unused comparitor to change states, and add noise to the power line, etc. All it takes is a tiny change for one pin to be above the other.

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    very nice! clean and pro!

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    Flashaholic Aepoc's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    very inspiring!
    22, 47.867, [Ar] 3d2 4s2, hcp, 21.9 W/(m·K), 420 nΩ·m(at 20 °C)

  19. #19

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Beautiful work, looks like an industrial piece of art. How many lumens is that putting out? Someone needs to build something like that with a bunch of reflectors or lenses and make a cannon of a search light with high cri (ha!).

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Nice project work. I am getting the urge to built up a photo light for personal use. - I hope you don't mind if I borrow some ideas from yours.
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    Flashaholic jeffosborne's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    HarryN, I would be flattered if my ideas are borrowed! Let me know if I can assist in any way. Here's a tidbit of info: my light could have supported 21 or 24 LED's and not just 18. The heatsink and fan operate rather leisurely, and could support more heat removal. More light is often good in the studio.

    Potato42, the aluminum is type 30-06, purchased at a local sheet metal shop. The finish on the light has not changed much over time, but I will consider an enamel clear coat for a future light. I built my own driver because I can (electronic design is my occupation), and because I wanted functions that off-the-shelf varieties do not offer. No PWM was one design objective, another being a linear regulator, and not switching regulator.

    Jeff

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    Flashaholic jeffosborne's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    HarryN, I would be flattered if my ideas are borrowed! Let me know if I can assist in any way. Here's a tidbit of info: my light could have supported 21 or 24 LED's and not just 18. The heatsink and fan operate rather leisurely, and could support more heat removal. More light is often good in the studio.

    Potato42, the aluminum is type 30-06, purchased at a local sheet metal shop. The finish on the light has not changed much over time, but I will consider an enamel clear coat for a future light. I built my own driver because I can (electronic design is my occupation), and because I wanted functions that off-the-shelf varieties do not offer. No PWM was one design objective, another being a linear regulator, and not switching regulator.

    Jeff

  23. #23
    Flashaholic jeffosborne's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Once was a pile of parts...

    What fun it is to build!

    Jeff
    Last edited by jeffosborne; 04-12-2011 at 05:53 PM.

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