I have been drooling after some nice led panels for a while now, but just can't justify spending a fortune to buy them.
These LED panel give a nice soft light source for photography, saves electricity, robust and won't heat much.
I am not a professional photographer, just enthusiast that sometimes has professional justify to build silly stuff like this.

I decide to do two big ones and one smaller that i would add battery later for outside shooting.

Step 1: Planning and Ingredients

My coal was to keep budget under 100 pounds for 3 led panels. Some how a 12v strip light felt like the best way to start. Also 12v meant that its easy to find power for. car batteries, power supplies and so on. How much light I would want? Well let see 5 amp feels like maximum amount of power I want to draw and 5M 300-SMD 5730 LED strip rope light white looked like a good model. (although later found it to be too cool near 9900k) there is a warmer version also. 5730 LED where 0.5 watt each and strip light was split in group of 3 LED's, so these can be cut between these groups. That was a good start for some calculations this site came handy.

http://ledcalculator.net/

So now I know that my bigger panels would take 99 leds and smaller would have 81 and you can left only 36 on by switch, if you want to increase battery life.

So where to house them. First looked into buying some aluminium briefcases for it, but then remembered that I had previously bought some aluminium school cooking containers from 70s for possible iPad and laptop bag, but now that project would wait and these cases would get a new purpose. I think these where perfect for the task. bigger panels where built on one container lid as one panl and botom

I wanted to able to dim this led although I know that it might be a possible problem and introduce flickering specially in low power, but then I decided that I will be mostly run them full power and I just went a head with a simple premade led dimmer.
Some switches i tried to find ones with bit of a retro style.
I think aesthetics are important I can find myself enjoy something I have built more if it also looks good.

List of parts

3x Led dimmer 12/24 volt 8 amp
price of one 9£

3x power supply 5 amp
price of one 5£

Led strip
5M 300-SMD 5730 LED strip rope light white
40£

3x power switch
price of one 2£

3x power plug
price of one 2£

aluminium tape

some electric wire

total 94£

additional stuff

plexiglass
20£

mounts
14£

3x photography light stand
price of one 9£

Step 2: Led Placement

First I tested lights in groups this is important because I found out that 12 of my LEDs did not light up.
Remember to buy more than you need.
So after getting rid of non working ones I cutter the strip in smaller right length strips. And placed them pre planned position. And started to cut out wires and place switches on right places to get an idea if all would fit well.

I laid few layers of tape under led strips for isolation and then temporarely taped them in place.
clear tape works here fine as it does not block reflections from the aluminium container.

Step 3: Dimmer

I opened one of the dimmers to see what it had eaten. See if i can reduce the size of it and I was really pleasantly surprised that it was perfect layout and it even had dimming control with wire so I could place it freely.

note: Remember these kind of dimmers are very basic and works with Pulse Width Modulation principle. witch means that when led is dimmed it actually cuts the current for really short periods rapidly. You can't see this by eye, but when used for video or photography camera can pick up these cuts and it looks like a flickering or produce artefacts when shooting video.
This comes more problem when lights are dimmed a lot and high speeds for shutter time is used. Problem goes away when full power is used.

Step 4: Holes

After that I took few measurements for rest cables. Then I took the LEDs off and drilled holes for DC power input, dimmer control Knob and on/off switch. It's good to drill your holes for mounting also. If you are going to add plexiglas or gel in front it's also time to drill mounts for that. For me it was a late update so I did this in the end.

note: buy round DC plug so you can mount it easy just by drilling one hole. My power supply had DC 2.5mm male plug so i bought corresponding 2.5mm female plug.

Step 5: Testing Electronics

It was time to test electronics and see if everything would still works.

note: be careful that no electric connectors touch metal or short circuit when you test. duhh :)

Step 6: Taping to Final Position

Then I covered all connectors with electric tape for insulation and used aluminium tape to tape strips in place. So far with my tests these panels are very cool and the aluminium body displaces the heat very well.

note. I used aluminium tape to maximise reflecting surface on the panel.

Step 7: All Done

Voila everything works. I made some measurements. Light temperature 9500k too cool so for now i decided to add panel of frosted slightly brown tinted Plexiglas which works as protection, light diffuser and changes light to more workable 7700k not perfect but closer.

This is a first version of these lights. I am really happy about the results, but here are few things i might re-think or do differently for next version.

Mounting. well this didn't go as planned I first bought flashgun mounts that seemed like perfect place to start, but company that sold them could not get them delivered and returned my money. I was running out of time to enter 4th Epilog Challenge so I went a head and made them from mounts that I already owned ment for surveillance cameras.
Not ideal,flimsy and i don't recommend.

warmer leds or even adjustable color temperature

i would place every panel in own case though having two panels in one case lid and bottom takes less space. its not handy when you just need one also gives more freedom in control, switch and power plug placement. By placing them only one end can make more robust design.

Light intensity not measured with professional equipment just simple sensor.

without plexiglass

next to panel 5700 lux
1m 250 lux
2m 100 lux

with plexiglass

next to panel 2700 lux
1m 170 lux
2m 80 lux

Thanks to my girlfriend for being the best assistant ever.

Thanks to everybody for reading :)