Let's talk about Lighting

All about lighting. LED, CFL, Halogen, Other? Questions and info about lighting go here.

Re: Let's talk about Lighting

Postby Koyaanisqatsi » 31 Mar 2011, 03:05

If you're triggering the camera electronically, you could sync the LEDs and the camera so that you don't have to change the brightness of the LEDs to shoot. LEDs are dimmed via pulse width modulation (PWM) in many cases. If the PWM frequency and duty cycle were based on the shutter speed, the LED would be on for the same duration as the shutter is open, effectively full brightness, even though the LEDs look dim to our eyes.

For example, you decide that 25% is a nice working brightness, and you have enough light at 100% brightness to shoot with a 1/250 sec shutter speed. That means you want the LEDs to be on for 1/250 sec and off for 3/250 sec. 4/250 sec = 62.5Hz. So you need a 62.5Hz PWM frequency (about the lowest that won't give you a headache). At 25% brightness, trigger the camera when the LEDs turn on and the shutter will close when they turn off. This would be a good Arduino or other microcontroller project.

I created a concept circuit, but I need to verify a couple significant details before I post it. I'll try to put that up in the next few days.
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Re: Let's talk about Lighting

Postby daniel_reetz » 31 Mar 2011, 10:32

Koyaanisqatsi, can you send me an email (my email is in my profile)?
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Re: Let's talk about Lighting

Postby anvit2a » 05 Aug 2011, 18:13

Anyone that can inform me a bit more about the Cree XP-G R5 Cool White ?

What is the "turn on" values? how much voltage to just turn on the led?
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Re: Let's talk about Lighting

Postby stevede » 07 Aug 2011, 13:53

Heat sinks. Finally, at a decent price, if you have patience.

http://cgi.ebay.com/Aluminum-Heatsinks- ... 0678603414
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Re: Let's talk about Lighting

Postby Koyaanisqatsi » 15 Aug 2011, 01:53

@anvit2a: LEDs are "different" from other light sources as they are not dependent on voltage but rather the current flowing through them. They usually operate around 3.2-3.5v or so per LED, but you'll burn it out if you apply voltage without current regulation. LED drivers are current-regulating devices that adjust the voltage to whatever level is necessary to maintain a specific current level through the LED. The Cree XP-G can handle up to 1500mA of current. Its ratings and specifications, however are based on driving it at 350mA.

Take a look at the Cree data sheet for more information:
http://www.cree.com/products/pdf/XLampXP-G.pdf
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Re: Let's talk about Lighting

Postby Turtle91 » 21 Aug 2011, 02:39

Hi all - First time posting becase I've been studying all the info on here for the last couple of months. It's amazing all the different areas that building a scanner can take you - stuff I haven't looked at since college 20+ years ago - electrical circuits/programming/light waves & optics/mechanical engineering/pulleys. It's been an adventure!

At first I was surfing how to properly format ebooks to meet the ePub "standard" and found a video of Daniel and his instructible and said "that looks cool", then I skimmed a couple builds and printed out the new standard and went to the store with that shopping list. Ended up not building it - yet - because I got caught up studying all the great ideas that everyone has been putting up here. I decided to steal an idea here and there and come up with my own. I hope to post it on here soon.

I noticed the new Cree datasheet (http://www.cree.com/products/pdf/XLampXP-G.pdf) says they did some more testing and have validated ALL their LED's (including older ones) can be run up to 1.5 amps. I assume that means you can get brighter light... Although from what I understand the Buckpucks still only put out 1 amp so you are limited if you are using those.

I also noticed that Cree has the XP G U1 (XPGWHT-U1-0000-00AE7) which provides a CRI of 90+. I was planning on ordering a few of those and playing with them - that is, if I can find anyone who actually has them - Cree doesn't seem to have the most user friendly product ordering process! Has anyone used the XP G U1? Or do you think that the DX Cree Q5 gets good enough results when scanning color images? - I haven't been able to find what the CRI value is for the Q5.

I have a question about the LED circit setup (ref the 20+ years since I've played with wires :oops: ). I want to have an on/off switch for the lights, and the dim working lights. When I hit the switch I want the lights to go full bright and then back to working intensity when I release the switch. Daniel mentioned
daniel_reetz wrote:...- if you connect the +5V output [ref] of the buckpuck to the control pin [ctl], it turns off. If you have a resistor on it, you can adjust the level. You can have a switch with a resistor on each pole, which will give you a medium and high level....

What I think this means - please correct me if I got it wrong - is that I put about a 350 ohm resistor in my switch which limits the current when I'm NOT pushing the button - giving me a dim working light.
When I push the button this bypasses the resistor - cuts the connection between ref and ctl completely - and the lights go full bright. In Daniel's picture - which I drew on below - it showed another resistor that I couldn't figure out the need for... :? Anyone have an idea if that is necessary??
Image

Thanks for all the great work you guys are doing!!
Turtle91
 

Re: Let's talk about Lighting

Postby daniel_reetz » 21 Aug 2011, 12:04

Turtle91 wrote:I noticed the new Cree datasheet (http://www.cree.com/products/pdf/XLampXP-G.pdf) says they did some more testing and have validated ALL their LED's (including older ones) can be run up to 1.5 amps. I assume that means you can get brighter light... Although from what I understand the Buckpucks still only put out 1 amp so you are limited if you are using those.


It is true that you can drive the Crees as hard as 1.5A or possibly more at shorter durations. But the issue then becomes heatsinking - if you haven't played with one of these LEDs yet I highly recommend getting one and seeing just how hot they get at 1A. With a good heatsink, though, it shouldn't be too hard to drive them at that current.

Turtle91 wrote:I also noticed that Cree has the XP G U1 (XPGWHT-U1-0000-00AE7) which provides a CRI of 90+. I was planning on ordering a few of those and playing with them - that is, if I can find anyone who actually has them - Cree doesn't seem to have the most user friendly product ordering process! Has anyone used the XP G U1? Or do you think that the DX Cree Q5 gets good enough results when scanning color images? - I haven't been able to find what the CRI value is for the Q5.


There are many people competing for these new emitters - high end flashlight people especially. It can be tough to find them, but there are often group buys at candlepowerforums.com. Although I've done little scientific testing, I've found Q5's to be "good enough". Higher CRI will usually produce a better image. There's a mountain of weird marketing crap surrounding CRI. I intend to write about it soon to clear the air about LEDs and color rendition, but for me, soon will be about 3 months from now.

Turtle91 wrote:I have a question about the LED circit setup (ref the 20+ years since I've played with wires :oops: ). I want to have an on/off switch for the lights, and the dim working lights. When I hit the switch I want the lights to go full bright and then back to working intensity when I release the switch. Daniel mentioned
daniel_reetz wrote:...- if you connect the +5V output [ref] of the buckpuck to the control pin [ctl], it turns off. If you have a resistor on it, you can adjust the level. You can have a switch with a resistor on each pole, which will give you a medium and high level....

What I think this means - please correct me if I got it wrong - is that I put about a 350 ohm resistor in my switch which limits the current when I'm NOT pushing the button - giving me a dim working light.


That is correct.

Turtle91 wrote: When I push the button this bypasses the resistor - cuts the connection between ref and ctl completely - and the lights go full bright. In Daniel's picture - which I drew on below - it showed another resistor that I couldn't figure out the need for... :? Anyone have an idea if that is necessary??
Image


I used it to limit the brightness somewhat so I wouldn't need to use big heatsinks. On my setup the Crees are just stuck to a piece of aluminum. Nothing wrong with going full-brightness, I just didn't want to deal with the heat issue.
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Re: Let's talk about Lighting

Postby anvit2a » 24 Aug 2011, 15:48

I'm building my own "buckpuck" or adjustable power supply that will run my 3 crees.
I already got the circuit and solder it together and it seems to be working... need to do some tests and solder the 3 crees together instead of the weak linking i had done in the testings.

If people are interested i can do a tutorial or DIY buckpuck guide so other can do the same :) ...

The buckpuck is build with a LM317T and a few other compontens which is very cheap and the power can be a laptop powersupply or even a Computer Power Supply (I have tried using the 12V output and it gives me atleast 10,5V at 1000mA to drive the LEDs which is insanely bright when doing that! :D adjusting the brightness is done by a potentiometer and it is good so far...)
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Re: Let's talk about Lighting

Postby Turtle91 » 25 Aug 2011, 13:07

Daniel, thanks for the confidence boost! :D

I couldn't find a seller that was willing to sell only 4, and I was too anctious to wait - so I bought 4 of the Cree Q5 XR-E and a 3023 DE 1000 buckpuck. I guess I will wait on the high CRI LED's until they become a little more common.

The lights came in yesterday!! Yay!!

Anvit2a, I would very much like to see how you have put together your lights. I like to make sure of what I'm doing before I put a hot solder gun next to some computer chips!!

I was studying the buckpuck pdf and was having problems getting my head around the point that as you INCREASE resistance to the {ctrl} pin the lights would get BRIGHTER... :shock: That seemed counter intuitive and my confusion was definitely not helped by the completely innacurate (as far as I could tell) statement under figure 16: %IOUT = R1/50

I noticed the "Output current vs. control voltage" graph.

Image

Referencing the top line for the 1000 mA buckpuck - If there is zero voltage going to the {ctrl} pin then it will be full bright, and if we tie the 5V {ref} pin to {ctrl} the output will be zero. That all falls in line with what Daniel said earlier in this thread and what he demonstrated in the video.

I finally realised that the voltage going to the {ctrl} does not directly control the output current - instead there is some hidden voodoo magic inside the buckpuck that uses that voltage to LIMIT the current. The more the voltage coming into the {ctrl} the more the current is limited. The specifications state the Control pin adjustment threshold is 1.65V, the Control pin shutoff threshold is 4.2V, and the Control pin input impedance is 1000 ohms.

All my calculations up till now didn't take into account the added resistance of the {ctrl} pin itself. Once I added that value into the equations, all the empirical evidence coincided with the numbers. I made a table if anyone cares - that should work - showing the % of current output with different resistors:

Resistor
>=2000 ohms Full Bright
1750 ohms 85%
1500 ohms 80%
1250 ohms 75%
1000 ohms 65%
750 ohms 50%
600 ohms 45%
500 ohms 35%
400 ohms 25%
300 ohms 20%
<=200 ohms Off

If you are using the 1000mA buckpuck then the percentage is roughly equivilant to the output current.


Here are the equations I used:

I'll use a 500 ohm resistor for the example. Rctrl = 1000 ohms from specifications.

1) need to find the total resistance between {ref} and {ctrl}. Assumed resistors in series Rtot = R1 + R2... + Rctrl
Rtot = 500 + 1000 = 1500 ohms

2) need to find the current between {ref} and {ctrl} with a given resistor. Ohm's Law: V = I * R; rearranged I = V/R
I = 5V / 1500 ohms
I = 0.0033333334 amps

3) need to find the voltage drop over the resistor(s) - NOT including the {ctrl} impedance. Ohm's law again V = I * R
V = 0.0033333334 * 500
V = 1.6666667 V

That is the voltage DROP so we need to subtract that from the 5V {ref} puts out.
V into {ctrl} = 5 - 1.6666667 = 3.334

If you enter the "Output current vs. control voltage" graph at the bottom with 3.334 and go up until you intersect with the top line (1000 mA) you will get approximately .35 Amps output current (or 35% illumination)


I hope I didn't bore anyone and this helps someone else who may be having "issues". I sure hope I'm not the ONLY one who had issues with this.... lol

Cheers!
Turtle91
 

Re: Let's talk about Lighting

Postby daniel_reetz » 31 Aug 2011, 18:11

That's the most complete buckpuck understanding available here on the forum - thanks for writing it up, Turtle91! It's going to be great to have as a resource for people who try this method.
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