Lab lighting (for video recording) - Page 1
Forum section: electronics / general

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 12, 2017, 11:48:31 am
content: So, about two months ago, I decided to start a youtube channel. And it has been nothing but problems! From the overhead light washing out my face with it's awesome brightness - to the DC coupler in my camera dying and taking the camera with it - and then a business trip taking me away from my lab - and now...Flicker and banding.My overhead main lab light flickers at 100Hz. That was fine with my last camera before it died (720p @ 25fps) - but with my fancy new camera recording at it's fixed 30fps for both 1080p and 720p - and as a result there is pretty bad banding in the recording.Outstanding.The universe is trying to stop me making youtube videos! It's pretty funny when you think about itNow youcanget plugins to remove the banding/flicker in post-production - but they all cost money, and most don't work with Lightworks - so that's probably not the best route to go down.With that in mind, fixing or replacing the lighting would seem to be the way to go: what might you folks think?While I can get a pair of 135W studio lights for £50 - I'd be concerned about how cumbersome they are, and whether they would be bright enough to light the bench behind me when I'm doing a standing shot - but at the same time, if they work - then I certainly won't complainAnybody have any other other suggestions on how to rid myself of this flicker? Are the studio lights the way to go? Should I modify the existing LED baton light? (Bearing in mind that the baton light is a sealed unit that takes 220-240VAC- that's not to say I can't tear it down and modify it - just that it'd be a nuisance)

author: EEVblog
author_rank: Unknown
timestamp: November 12, 2017, 12:13:09 pm
content: Studio lights are tricky.Great if you have a fixed setup and tweak them to get them right, but if you are always moving around changing angles etc then the last thing you want is to have to re-setup your lights each time.I use my overhead ceiling LED light panels:They do an adequate job. Not perfect, but generally good in most scenarios I shoot.I do have studio lights on stands but they get in the way, and I only use them on special occasions.

author: Brumby
author_rank: Unknown
timestamp: November 12, 2017, 12:20:31 pm
content: Quote from: cprobertson1 on November 12, 2017, 11:48:31 amI'm going to jump straight in on this one .... DON'T plan post production processes like this into your workflow!!!Do WHATEVER IT TAKES (within your capabilities) to get as close to the ideal in the camera as you possibly can. Lighting, sound, flicker, shadows, focus ... whatever.There are two fundamental reasons for doing this.The first is that you will always achieve the best quality result by capturing the best quality raw footage.The second is the time you will save - not to mention the anguish and frustration from post production faffing around.

author: nctnico
author_rank: Super Contributor
timestamp: November 12, 2017, 12:23:25 pm
content: CFL with an electronic ballast flicker at a much higher frequency which also solves the flickering problem. Besides that you'll get much more life out of a CFL tube.

author: Brumby
author_rank: Unknown
timestamp: November 12, 2017, 12:24:28 pm
content: Quote from: cprobertson1 on November 12, 2017, 11:48:31 amGet some LED lighting (pay attention to colour temperature and CRI) and feed them with DC. No flicker. No banding.

author: coppice
author_rank: Super Contributor
timestamp: November 12, 2017, 12:29:26 pm
content: Quote from: nctnico on November 12, 2017, 12:23:25 pmA lot of CFLs chop the mains at high frequency, to avoid large magnetics, but still rise and fall in brightness 100/120 times a second. Take care what you buy.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 12, 2017, 03:15:24 pm
content: Quote from: EEVblog on November 12, 2017, 12:13:09 pmI forgot you done that video! Aye - the overhead lighting seem like the best option - as you said, much less hassle! Not too expensive either - I was expecting them to be moderately expensive - even the local prices aren't too bad (see below).Quote from: Brumby on November 12, 2017, 12:20:31 pmAh, definitely the case - I believe you mentioned something to that effect my my original post back in September when I was trying to figure out what camera I wantedQuote from: Brumby on November 12, 2017, 12:24:28 pmThat seems like the way to go - I've been looking at LED panels similar to what Dave has - the local prices aren't too bad:1200x300mm @ 4000lm w/ driver = £38 each1200x600mm @ 5600lm w/ driver = £75 eachChoice of 4000/5000/6000kDrivers are LiFud constant current drivers in 40 or 70W depending on the size of the panel.Given the size of the lab I'll need two of whichever size I go with - reckon I can get away with the 2x 4000lm 300mm wide panel lights?The next question is: which colour temp should I go with? My current light is 4000k (which I'm comfortable with) - but I wonder if the higher 5000k might make the lab look better at the expense of colour acuity?Many thanks for all the tips from everybody! Very much appreciated

author: nctnico
author_rank: Super Contributor
timestamp: November 12, 2017, 04:38:09 pm
content: Quote from: cprobertson1 on November 12, 2017, 03:15:24 pmIMHO 5000k is a neutral white. Less than 5000k becomes yellow and more than 5000k becomes blue.I have 5000k CFL tubes with the best color spectrum Philips offers (900 series) and I think my pictures look better than with the old tubes. It is worth checking the color spectrum as well because this is also an important factor. Not just for taking pictures but also when looking at whatever you are working on.

author: rstofer
author_rank: Super Contributor
timestamp: November 12, 2017, 04:44:20 pm
content: Regular overhead lights MIGHT do a good job under some circumstance but, basically, they are made to deliver horizontal footcandles (down on a horizontal surface) rather than vertical footcandles (at some angle to the subject, probably not actually perpendicular).Note the picture of Dave in the link above (I didn't watch the video). His face is entirely in shadows.If you Google for 'lighting for video conferencing', you will get some pictures of ceiling mounted fixtures for video conferencing. Note that they are all aimed, in one way or another, to provide vertical footcandles and eliminate shadows.Light fixtures for video conferencing tend to be pretty expensive (small market).You certainly don't have to use specialty fixtures but it is important to consider where the vertical footcandles will come from.I doubt that you can get the tested photometry curves for Home Depot fixtures but a fixture like this throws a LOT of the light at a 45 degree angle:http://www.visual-3d.com/tools/photometricviewer/default.aspx?id=15227Compare that with this fixture which throws the vast majority of light straight down:http://www.visual-3d.com/tools/photometricviewer/default.aspx?id=15216There's no reason you couldn't just hang a couple of fixtures at a 45 degree angle. They won't be in the picture so nobody will know how it is done.

author: rstofer
author_rank: Super Contributor
timestamp: November 12, 2017, 04:53:20 pm
content: I would spend less time wondering about lamp color temperature and more time worrying about Color Rendering Index (CRI). You want something over 90. Higher is better!http://lowel.tiffen.com/edu/color_temperature_and_rendering_demystified.htmlThe difference between Cool White and something with a 90+ CRI is DRAMATIC!

author: Benta
author_rank: Super Contributor
timestamp: November 12, 2017, 05:29:02 pm
content: For a perfect continuous spectrum, halogen is the way to go, preferably running on DC. Experiment with a number of spots around the object to keep shadows under control.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 12, 2017, 10:45:27 pm
content: @rstofer - no CRI listed for the lights I was looking at - I suspect they're in the 80-90 region based on similar panels. To be honest, I'm nottooconcerned about the CRI - the majority of shots in the lab will be of circuit boards and teardowns; with the next most common shots being standing shots in front of the bench, or beside a whiteboard - so if the colours are washed out it won't be the end of the world. Obviously, not an ideal situation - but I need to compromise due to the cost.The balance of vertical/horizontal intensity is an interesting one - I actually encountered issues with the current overhead light being far too bright relative to the reflected light from the rest of the lab. I ended up compensating for it with some fill lights or a reflector - more of a workaround than getting it right in the first place though. If I do end up going for the panels and I end up requiring them to be tilted, I'll see if I can put them on brackets that allow it to rotate down from the ceiling when I'm recording - or sit flat when I'm not.I've also just discovered that regular incandescent bulbs also flicker at 100Hz - huh - I've never noticed before; makes sense if you think about it though.Interestingly, I've also noticed that my led bulbs with the artificial filaments don't have visible flicker on the camera - if I recall correctly, the yellow material on them is luminescent - and the LEDs in them cause it to glow - making me think that it is flickering but the overall luminescence is being averaged out by that luminescent material.Butif that's the case - I would have thought the thermal mass in a tungsten bulb would also average out the flicker a bit... unless they have less thermal mass than I thought they did...?I think I'll go for the panel lights in a week or two once I get the funds together.Video quality isn't paramount for the first few videos. While I refuse to put out something flickery, I can certainly make do with smaller (flicker-free) lights for bench shots - and make best use of daylight in combination with a fill light for the standing/intro shots until I can upgrade the ceiling lights.

author: rstofer
author_rank: Super Contributor
timestamp: November 12, 2017, 11:41:46 pm
content: FWIW, incandescent is the 100 CRI standard. It is considered perfect. Everything else is something less.I know exactly nothing about making videos. I do know a bit about lighting and CRI - just a bit. If you are going to take a video of a PCB, I would think CRI would be the number 1 criteria. You can always adjust for brightness with the camera.Around here (US), the lamps at Home Depot and Lowes do have the CRI on the sleeve. Especially if it is a good number. High CRI lamps cost a bit more so they have to justify it somehow.Philips makes a bunch of 90 CRI fluorescent lamps and, as you can see, color temperature can vary all over the map. Pick one! It's the CRI that's important.Here is a selection:http://www.bulbs.com/90+/Fluorescent_Bulbs/results.aspxHere is the one I would buy:http://www.bulbs.com/product/F32T8-TL950-32WAnything with a CRI of 98 is going to have correct colors. You might even be able to read resistor colors in the video.I'm pretty sure Philips builds lamps somewhere in Europe.I'm also sure I don't understand what the EU is doing with respect to fluorescent lamps.It looks like you have a plan. Have fun!

author: StillTrying
author_rank: Super Contributor
timestamp: November 13, 2017, 12:49:18 am
content: Quote from: cprobertson1 on November 12, 2017, 10:45:27 pmWhere've you bin!The first image here is the light output of a 20W 12V halogen switching on, as you can see the 100Hz light ripple is about 12%. A 60W 230V incandescent was the same.They have enough thermal mass that the peak in light output is well passed the peak in V/I/W.https://www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 12:56:16 am
content: Quote from: StillTrying on November 13, 2017, 12:49:18 amIt should be obvious that an incandescent lamp will show some amount of flickering, but the extent takes a lot of people by surprise when they look into the issue in detail. The resistance of an incandescent lamp filament goes up and down so much with the cycling of its temperature that it results in something like 10% to 20% THD in the current waveform.

author: StillTrying
author_rank: Super Contributor
timestamp: November 13, 2017, 01:16:22 am
content: Quote from: coppice on November 13, 2017, 12:56:16 amUsing the scopes (simple)math to do V/I, I tried a few times to detect any 100Hz change in resistance, although the cold to hot resistance change is a large 0.4R to 6.4R, I never managed to detect any 100Hz change in resistance, I don't think the resistance change is all that big when the filament is hot.This post shows V, I and W. If you can think of a way to detect the 100Hz change in resistance post it there and I'll have a go!https://www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1318658/#msg1318658

author: Brumby
author_rank: Unknown
timestamp: November 13, 2017, 04:01:41 am
content: Quote from: rstofer on November 12, 2017, 11:41:46 pmI would lean the other way. Certainly the higher the CRI, the better, but for general photography where colour accuracy is not paramount, I would focus on colour temperature. Don't even look at anything under 4000ºK and I agree that over 5000ºK is too blue. Within that range you should be OK, especially with a camera that will allow you to set the white balance - preferably manually.QuoteYes you can, but make sure you have sufficient illumination so that camera adjustments are only 'fine tuning'. Don't skimp and find yourself trying to dig out a bright image by pushing the camera to its limits.This goes for any camera settings.

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 13, 2017, 07:54:59 am
content: Quote from: coppice on November 13, 2017, 12:56:16 amInteresting I always assumed that it stays hot enough to stay bright throughout a whole cycle. I oddly cannot notice the flickering on them but can notice on other types of lights like LEDs. How was this tested, with a photo cell? I could see the current "flicker" though because as the voltage goes up, the current will too. There is probably an interesting current usage profile as it warms up too. Now I'm curious to play with this on a scope. Throw a resistor in series then probe both ends.

author: Brumby
author_rank: Unknown
timestamp: November 13, 2017, 09:31:17 am
content: Quote from: Red Squirrel on November 13, 2017, 07:54:59 amThe flicker from incandescent light globes has been known for decades - and has been used as a frequency reference in one consumer product in particular...Remember the humble turntable? Some had their own strobe light and markings - but you could get strobe discs that sat on the platter and the flicker in the room lighting would produce the strobe effect.Typically 4 bands - for each combination of 50Hz/60Hz and 45/331/3rpm

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 09:56:48 am
content: Quote from: StillTrying on November 13, 2017, 01:16:22 amYour waveforms actually show the changing resistance effect. Why do you think some of them don't look like clean sine waves?

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 13, 2017, 10:41:41 am
content: @Coppic/StillTrying: aye, the extent of the flicker certainly caught me off guard - as you mentioned, that they flicker is to some extent obvious - I just never bothered thinking about it before - didn't even cross my mind actually!@Brumby: Aye, getting it right the start is definitely the way to go - only so much you can do post-production - as I see it, things like deflicker and brightness correction are solely for fixing blunders - not an excuse for sloppiness in the first place.That said, there is only so much I can do within my budget - some compromises must be made; but I draw the line at flickering footage.I'll be sure to provide before/after shots once I've attacked the ceiling and installed the new lights - I can probably put a video together of installing the lights too.Bit of a pity I'll be replacing the existing light though; excepting the flicker, it was a pretty good unit! I might move it to the kitchen (though it's probably too bright for that)Hmm... I wonder if bypassing the existing driver and wiring in an external constant current driver would fix the flickering actually... I'll try tearing that down tonight and seeing if I can do anything with it.--EDIT--In fact... would simply increasing adding some larger caps on the existing driver's output reduce the flicker? (the intensity of the flicker that is) - please note I have no idea what the existing driver topology is, nor if there is already a really large cap across the output - just throwing random ideas about as they pop into my head.

author: StillTrying
author_rank: Super Contributor
timestamp: November 13, 2017, 06:30:23 pm
content: For those interested... A photocell, LDR, or phototransistor are all probably too slow even at 100Hz, andnon-linearto capture an accurate view of a bulb's light ripple level.Probably the simplest and quickest way to look at an incandescent bulb's light and ripple is just a SFH213 photodiode(271226770355), in parallel with about 1k and a X1 scope probe.But you'll have to get the photodiode close enough to the bulb to give a DC photo output of about 50-100mV, and by then switching the bulb on and off you can get the 0% light level and the 100% level on the same scope capture, and estimate the %age of the light ripple level around the 100% level from there.That should be sensitive enough to capture the light from mains LED sources, or the IR from a remote - at a few mm distance, but will struggle with the diffuse light from a CFL.If you need more bandwidth and/or sensitivity you have to do it differently."Your waveforms actually show the changing resistance effect."Only very indirectly. They show the 100Hz 12% variation inlightlevel."Why do you think some of them don't look like clean sine waves."The peaks in light are always sharper than the peak dips in light, and the rising and falling slopes in between are different, spread out a bit it looks like a water wave.I've just posted one of the attempts to detect the 100Hz change in resistance using math V/I.https://www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1348515/#msg1348515

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 14, 2017, 03:30:31 am
content: Actually, how fast are solar cells? That could maybe be another way too. Never even crossed my mind to hookup a solar panel to the scope. I want to play with that when I get home now.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 14, 2017, 08:34:14 am
content: Quote from: Red Squirrel on November 14, 2017, 03:30:31 amAt a guess, I would reckon they would make poor sensors (in this application) - solar cells are optimised to collect energy from light, rather than quickly responding to it. I also seem to recall that solar cells have a relatively high capacitance - making me think one would struggle to get decent readings of flickering light.Perhaps one more versed in solar cells/photodiodes can expand on the subject?Regardless, I'm going to be shoving some probes into my USB-solar charger once I get in from work - you've piqued my curiosity on the subject xD

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 16, 2017, 10:17:06 am
content: I tried measuring the flicker with my USB solar panel last night - I gotsomethingbut didn't bother finding out if it was noise from the PSU or not; I did however notice that there seemed to be a higher-frequency square wave overlaid on it though (as if the power to the light was being chopped as well as flickering at 2x AC)I didn't bother investigating as I was in a rush to tear it down and have a look at the driver and it was getting pretty late.Once I cracked the end off the IP67 casing, the inner assembly just slid out.Just an aluminium extrusion with a driver on the back (looks decently made - if a little simple; just a buck topology if I'm not mistaken) - that passes through to the front where there are a pair of LED PCBs - each mounted in another aluminium extrusion that is riveted to the main extrusion at both ends.That works out as two strings of 160 LEDs in parallel; which will be why it's so brightBoth the PSU and the LED PCBs are labelled "T8BF3" - can't find any data on it I'm afraid. Lots of weird result and word salad, and even an offer for the domain name "www.T8BF3.com" (I'm surprised nobody has snapped it up yet!) -but nothing that doesn't make your eyes water when you try to read it.Weirder still, the top of the PSU says "43W" but on the bottom there's a box with a blob of glue in it that says "60W" - which also happens to be what the LED PCBs say on them... which I don't really get (unless it's taking 60W in total, and outputting 43W to the lights... would that not make it ~70 efficient?)Either way, before I go out and buy panels for the ceiling, I'm going to try installing a constant current supply in the existing fitting.Quick sanity check(s):a) Am I right in thinking that a constant current driver will reduce/remove visible flicker?b) Am I correct in thinking that to get the required spec for the replacement driver*, I can just measure the voltage/current of the existing fixture while it's in-use?c) Am I right in thinking that a dimmable constant current driver will cause flicker when it'snotat 0 and 100% brightness? In which case, will there be (what I shall loosely call) resonant points where the FPS in in sync with the flickering at various brightness levels and flickering/banding will be reduced near those points?*there's no specification markings on the current driver except from "43W" on the top and "60W" on the bottom.