Chronos => Chronos User Discussion => Topic started by: CS223 on April 04, 2020, 10:47:23 PM

Title: Lighting question
Post by: CS223 on April 04, 2020, 10:47:23 PM
Been reading the various threads on lighting and the discussion on the LED modules. I was wondering if  anyone has tried using those LED light bars that they sell for vehicles? They are obviously 12V. I have two 24Ē versions mounted on my tractors roll bar and they are blinding bright. I paid something like $55 for the pair. Iím thinking of lighting a scene where you might normally use one or more of the halogen work lights.
Title: Re: Lighting question
Post by: SergeyKashin on April 05, 2020, 01:16:00 AM
they have a very low color rendering index, you need to understand how many watts they are
Title: Re: Lighting question
Post by: Nikon1 on April 05, 2020, 03:45:48 AM
They for sure look pretty bright, but keep in mind, that most of the higher power LED-Chips can Actually MAKE YOU BLIND, because of how powerfull they are (if watched too long directly from Short distance). If i could take a guess, i would say that those Car-LEDs propably are 5 to 20 Watt each at max. that is sure bright for any light on a car, but not so bright compared to those High-Power LED-Chips.... The "classic" ones, that have been around for many Years have 100W Power, Now there are even Newer Versions with 200, 300, 500 and seemingly even higher Power Versions Like 1000 Watt! Just watch the video, which i linked in the other thread from the Beyond the Press chanel on YT. Those Lights are so bright, that they needed to wear two pairs of Sunglasses to be even able to see anything, because it just was THAT bright. Those are no joke. Pretty sure that LED-Setup they used to Light the Chronos Ring Footage would be able to overpower the sun by quite a bit at that distance....         
       However, i would seriously be impressed if any LED for Cars had more than 20 to 40 Watt. Additionaly, like SergeyKashin allready said, they most likely have pretty bad color, since they just need to make it bright, and your eye doesnt care that much about Color, but cameras do very much. Most of those cheaper LEDs, which are most likely used in those Car ones will not be a proper white color, but rather a bit green tinted. You Could Propably still use them (i did use cheap ones, but its a pain...), if you know very well about this, and how to correct for it, but as soon as you have mixed Lighting Sources (Sunlight/ tungsten), you will clearly see the green color cast from the Cheap LEDs. That is one of the Reasons, why Bright and high Quality Professinal LED-Lamps built for Cinema and Photography tend to be rather pricey, since they (mostly) use the more expensive LED-Chips with better color (higher CRI=Color rendering index)
Title: Re: Lighting question
Post by: CS223 on April 05, 2020, 05:56:13 AM
These are what I was referring to. The are 120W and 6000K color temp so that probably isnít the best for CRI. 5000K I would think would be better. My application is primarily going to be machine and mechanical diagnostics which the monochrome model would be best suited for but I donít want to limit myself so Iím planning to go with color.
Title: Re: Lighting question
Post by: NiNeff on April 05, 2020, 08:11:09 AM
Those are quite large modules (24 inches) with only 120W total, that's quite a low light-density for high-speed. Depending on your setup and conditions, it might still work or even be a good solution, but in general you might want to look into even more light packed into a smaller area. This however comes at the price of needing cooling which is noisy if you go with air.

I hade good results using a few of those modules:
 if you have the space and want it really bright, you could even stack them together:
Title: Re: Lighting question
Post by: Nikon1 on April 05, 2020, 09:19:02 AM
About the Monochrome vs. Color- Thing: There are a lot of advantages to the Monochrome version, if you dont actually need color, you should really think about getting a Mono one if you are only doing diagnostics. Main Advantages of the Monochrome: You need literally half the Amout of light, and its quite a bit sharper.   
   About the 5000K: Those Kelvin Numbers (5000K / 6000K) tell you the Color Temperature, CRI is completly independent from Color Temperature itself. Color Temperature tells you, how "Warm" or "cold" a Light is. So if you put an Light with an Color Temperature of 2500K next to an Light with 10.000K Color Temperature, you will see, that the 2500K one will look very "Warm" (Yellow/Orange) and the 10.000K one will look "Cold" or Blue next to the other one. CRI on the Other Hand doesnīt really have anything to do with The Color Temperature. It is more about the Quality of the Color, and how well the Light will Reproduce Skintones and Other Important colors. Its quite Important for any Kind of Filmmakinkg and Photography, but for Technical stuff and Diagnostics it is indeed not. So for your Application you could use even very low CRI Lamps, if you wanted to save a buck or two.   
   Now about the Power: That depends on a lot of different things.... For One, it depends a lot on Framerate. if you are only using the Chronos for 60 to a few 100 Fps (maybe even 1000) and could afford to shoot always with an wide open Lens (Background will be unsharp and only a very small Layer of the Image will be in Focus!), 120W Might be enough to Make your Image Bright enough to see what is going on. But, as NiNeff allready pointed out, if you want to use higher Framerates (way above 1000Fps), 120W LED will look like nothing pretty Quickly. Also keep in Mind Object size (Whatever you are Filming) and Lamp Size. Light will drop in intensity by Square if you double Distance. That Means, if you have a Large Scene, you need crazy amounts Of Light. Also, if you shoot very small Objects, you can get way more Brightness with an Small Chip Close to the Object, than with an Large Area Lamp (Which just from its own size cant get the same amount of power that close to you object).   
    so, in Summary: If you only want to do lower Framerate Diagnostics-Stuff with Medium Sized Objects and have enough space, 1 to 6 of those vehicle Lamps will propably work well enough for you. but for anything else, maybe think about High-Power-Single-Chip LEDs and maybe even an Monochrome Camera.
Title: Re: Lighting question
Post by: CS223 on April 05, 2020, 08:23:31 PM
Thanks all for the kind replies. I clearly have a lot to learn so I'll keep reading and watching.