Building a custom short distance, super bright, wide angle, evenly distributed light

[Night Watcher]

Hello everyone,


Been researching flashlight for the last few weeks, and I'm happy to come across this forum.


Even after a lot of research, there is a ton that I don't know, and I would appreciate if you can correct my idealistic hypothesis.


I am working on a special project where I would like to take photos with my drone (DJI Mavic 2), but I would like to attach a light bright enough that make casted sunlight neglectable.
Why brighter than casted sunlight? Because I need to take a high brightness photo, and the light will go through multiple filters making it a bit less bright, and depending on the capture conditions might need to shoot in daylight. I might be able to get away with slightly less bright, but that would be the ideal solution.


I will be taking pictures from a distance of 3-10 feet (1-3 meters), and have no intention of taking photos of distant subjects.


DJI drones do not have a way to detect when a photo is being taken to activate a strobe flash light, and since I am taking images at high shutter speed, it is hard to manually synchronize a strobe with the camera, therefore I would need a continuous light source instead.


I am looking to build a light solution as follows:

• 70-80 degrees field of view
• Light has to be evenly distributed around that area, therefore the hotspot would be covering the entire view with no dark cross in the center. As long as the hotspot covers the field of view, I do not care about falloff, though ideally, I prefer keeping it to a minimum.
• Light casted in that area would be 4 to 10 times brighter than casted sunlight.
• The Flashlight will have to continuously run for 20 minutes max
• The entire solution including battery and heat-sink, needs to be below 0.88 pounds (400g), and the smaller in size the better.

I am considering using 2-4 XHP70.2 LEDs to place on either side of the drone, or in the center below the camera.
For the power source, I am considering a 4S Lipo battery 4S 850mAH.

• Do you recommend another LED?
• Can a single driver run all LEDs or do I need a driver for each?
• Where can I buy a reflector and lens, and how to pick them?

Components budget $150-$350


I appreciate your guidance and suggestions.


Thank you in advance!

 

[devryd]

Firstly, define what you mean by "4 to 10 times brighter than cated sunlight", please. Secondly, running a flashlight on max is no problem continuosly, if you chose your max low enough. You can run a xhp70.2 up to 20A as far as I know. For that, you would need a lot more than this battery pack.

 

[DIWdiver]

Let's see...
A 3m circle is about 7m^2. In our office, we keep it about 500 lm/m^2. The production floor is about 1000 lm/m^2, and that's too bright to work at a computer for long periods. You want 4 times, minimum, so 7x1000x4 = 28,000 lm.

If you reach pretty good efficacy of 150 lm/W, you need about 28,000/150 = 187W. Unless your driver is super efficient, you will need over 200W from the battery. To run for 20 minutes, you need 200/3 = 67 W-h. Your battery can produce about 12.6 W-h, so you'd need at least 6 of them.

If you are talking about normal sunlight, you are at least ten times that number. If you are near the equator on a sunny day, it's over 100 times.

So before going any further, it's pretty important to clarify exactly what you mean by "casted sunlight". I suspect you are going to find that a synchronized flash is the only way to achieve what you want. Even that might be a challenge in 0.88 pounds.

 

[Night Watcher]

Thank you both for the reply.

I see these are not reasonable challenges.

While I can't synchronize a strobe light with the shutter, I guess I can just turn on the light, take the photo, then turn off the light, that would save a lot of power and heat.
Follow up question, does the light take time to reach full brightness?

To explain "Casted Sunlight", I am not allowed to fly a drone at night. I will need to fly the drone during the day in a open field lit by the sun. I guess if I'm on a good day it might be overcast.
The problem is that sunlight has ambient and direct shadows that I don't want. The plan is to blast the surface with light and lower the shutter speed making sunlight shadows very low.

 

[DIWdiver]

Okay, so at the very least, on an overcast day, you need ten times what I calculated, or 1870W. Even with a 20S lipo pack, where voltages are starting to get hazardous, near end of charge you'd need to pull 2000W at 60V, or 33A from your batteries. I know you can pull 20C from some cells, which means you'd need 33A/20C = 1.65A-h worth of cells. So you'd still need a 20S2P pack just to cover the current requirements, without regard to capacity or runtime. You'd get about 2-3 minutes total burn time.

If you are willing to sacrifice even more total burn time, there are techniques like charging up a capacitor gradually (requiring less current from the batteries) then discharging rapidly. This is how battery operated flash units worked before LEDs. In this case a supercap might be the thing to use. So maybe 20S1P for 60-90 seconds total burn time, or 10S1P for 30-45 seconds total. However, you still need a 2000W LED driver, 2000W (pulsed, so nothing like continuous) worth of LEDs, and some heatsinking.

These numbers are starting to look achievable with current technology. But I doubt you will find the necessary hardware available off the shelf, or within your price range. Your weight limitation makes it all the more of a challenge.

 

[Night Watcher]

For the LED there is the YUJILEDS® High CRI 95+ COB LED - 900H - 1500W one, which I think is close enough but cost 1350$
it needs like 4 massive drivers, and massive heatsink, and massive power source, which is feasible but not practical.

What about using 2 IMALENT MS18, they can deliver 100k lumen each.

 

[lightfooted]

Perhaps a more reasonable approach, rather than try to overpower the sun with a steady light source...would be to try to build a remote trigger for a camera flash or rather a way for the flash to be triggered when the built in camera takes a picture. I would suspect that this is more likely to have been attempted already or perhaps a drone related forum has developed a solution.

 

[Night Watcher]

Perhaps a more reasonable approach, rather than try to overpower the sun with a steady light source...would be to try to build a remote trigger for a camera flash or rather a way for the flash to be triggered when the built in camera takes a picture. I would suspect that this is more likely to have been attempted already or perhaps a drone related forum has developed a solution.

Thank you for the suggestion, I'm actually inspecting that solution as well on the DJI forums (feel free to recommend another), but no luck so far :/