Still in the process to design my DIY video light...Thanks to this forum things are going on, I think that I finally choose how to do a couple of things:
The driver will be a Taskled H6Flex driving 6 XML (3s2p), it's able to give them up to 3A that is the max current for them. The point is that with just 4 li-ion cells may be I'll need to lower a bit the current to have a decent runtime.
I'm drawing the components of the head and got this:
I'm planning to use a thin glass lens reinforced by the one-piece diffuser that its in contact with the heat-sink.
The idea is that heat will heat-sink also through the glass while being "supported" by the diffuser.
I wouldnt use thin glass but the thickest you can get. Or PC or Acrylic. Dont be so concerned about transmittance index of either its pretty minimal in relation to the water and a diffuser! Also dont worry about scratching it. I havet really put any significant scratches on any of my lens's and on a video light it will make no difference.
The heat will not very readily transfer through the glass. Make sure you use a decent sized heat sink that has an excellent contact path to the water for cooling or the who lot will cook very quickly.
I agree with packhorse. plastic lenses have very similar transmission characteristics. those few % won't make much difference. I doubt scratches would be a big concern, since it would only diffuse the light a bit more.
I agree with other comments. Woul also recommend 9 xmls at lower current, than 6 at 3amp. Eg 9 @ 2200ma give more light than 6 @ 3000ma, and with the h6flex you have more usable medium and low power levels (depending on how you configure driver). This will help with you battery constraints.
I'm not sure what you're expecting to get out of a diffuser, or do you mean optic? I wouldn't be diffusing bare LEDs as they are already matte and don't have enough punch as it it.
I'm also concerned that your screw in heatsink will make assembly more hassle than it needs to be. Ie wiring is a pain, though hard to tell from pic.
As I told you on a PM that is more or less what I'm trying to build, I saw that you pass form 6 to 9 XML on you device...Is not too much light? I'm absolutely novice in this field so I was trying to "imitate" what is on the market. I read a lot of very good reports about Sola 1200 lights telling that they give amazing amount of light, so I'm hesitating. I know that you are a professional in video sub, I visit your web and I've seen your videos and see that you're recording really deep wrecks. I'm a recreational diver looking for a device able to give color to my poormen photo/video camera recordings. I mostly dive in places with really good visibility.
Thats why I'm not sure about building a light with so many lumen. I'm not sure if I'll take advance of the extra money invested in more leds more batteries and end up setting the super-light to low power all the time not to burn the footage.
Here is a paragraph on one of this articles I was referring; "So, with all other elements of the two models of lights being the same, what is the significant difference between the Flux and CRI models? To begin with the Flux model shines with 5,000 lumens at 5,000 kelvin while the CRI model produces 3,000 lumens at 5,000 kelvin. Just how important a difference is this? In my opinion, after using the CRI lights on my Nauticam housing, the lumen level difference was not as great a factor as one might think. In fact, long before I ever tried out the Keldan lights it was becoming a personal opinion that too many manufacturers of underwater video lights were making too much of a big deal when advertising their light’s lumens ability. For close up or medium shots, too much power would blow out an image anyway forcing you to move to a lower setting. How colors are rendered underwater is a much more important consideration in my opinion."
A change from 3000 lumens to 5000 isn't huge, but it isn't quite trivial either. The color rendition may make the CRI model a better choice. The high flux LEDs have a color band where there is hardly any light. If something in your shot has those colors, they will look funny.
9 LEDs at 2200 mA is about the same power as 6 at 3000 mA, (because the voltage is a little lower) but you get more light because the LEDs are more efficient.
I did some quick calculations, and for 5% more power you get 13% more light. Or almost 8% improvement in efficiency. Or drop back to 2A and get a bit more light for less power. You'd have to decide if the extra cost is worth it.
All this assumes you keep the LEDs really cool. In real life, at 3A they are likely to be hotter than at 2A. This makes the difference even larger, but you have to make some thermal assumptions before you can estimate how much.
Sorry, I got mess up with my doubts about how many lumen do I need that I didn't comment the rest of your post.
First of all, I made a mistake of "direct translation" again, Damien you are right, I was meaning optics not diffusers. I'm planning to "imitate" Sola design as far as I can appreciate in the photos of their product. It seems to be a quite simple polished counterbore, I guess with and angle on 90º.
The idea is to make a "sandwich" with the glass lens and the aluminum reflector so that the part of the lens unsupported is just the 6 (or may be 9) counterbored holes for the leds. That's about 13mm diameter. I've try to find the modulus of rupture of the lenses I was planning to use but no way. I made some calculations based on other glass lenses and it seems to me that all of you are right and may be is too thin.
May be I should try to find a plastic seller in Zaragoza 6mm will be enough?
About screwing the heatsink...It's the idea I got trying to make it as light as possible. Secure the lens with screws as in Damien design imply a thick tube to have room for the screws. The other option I saw is an outside ring like maglites and other candles have. That involves making the treads is the lathe in a way I feel is a bit more complicated.
The wiring will be no problem (I hope) as I'll mount leds to the heatsink and then the driver in the opposite side. I'm planing to have room for them.
I'll post different draws as I can have time for making them.
Ok!! nice arguments DIWdiver, I did'n think on efficiency so deep.
I set a mail order for 6 leds already so I'll wait to have them at home and see how much room they will need. I bought ones on a 16mm star, a little bit big now so I need to find out if I can trim it anyway without breaking it.
I'll keep you updated with my design as soon as I can.