COB Ringlight

Miljenko · Post by **Miljenko** » Wed Sep 18, 2019 1:16 am

This 30mm variety could be nice fit between half of ping pong ball and objective front surface. If glued together it steals less than 1 millimeter from the working distance. In case of excessive heat, one could use this heatsink mounted reversed and fan removed: https://www.aliexpress.com/item/3305390 ... 2e0eS0Ih9o
It is only 55x55x12mm size, small enough not to be in the way on macro rails.

ray_parkhurst · Post by **ray_parkhurst** » Wed Sep 18, 2019 5:39 am

I've been using COB lighting for a while with no overheating issue. I don't run them super bright though. Maybe you'd need to do better heatsinking if you use them at or beyond their limits.

ray_parkhurst · Post by **ray_parkhurst** » Wed Sep 18, 2019 8:18 am

I looked back and realize I stated the ID was same between the 30mm ringlight and the Headlight COB I posted earlier. However, this is not the case. The Headlight COB has 17.5mm ID, and no metal flanges. The 30mm ringlight has metal flanges at 18mm, with the phosphor region starting at 20mm, and outer phosphor dimension of 27mm.

I added the outer dimension to the earlier image, see below:

Miljenko · Post by **Miljenko** » Fri Sep 20, 2019 12:34 am

Obviously we'll have to buy and test them all!

ray_parkhurst · Post by **ray_parkhurst** » Fri Sep 20, 2019 3:04 pm

Miljenko wrote:Obviously we'll have to buy and test them all!

The specific diameter is indeed important to me. For one of my applications, I'm trying for a specific range of illumination angles (45-55deg) with several objectives having a range of WD. I have a good solution using the 20XMM objective and the 40mm Angel Eye COB ringlight, but I'd like to figure out how to use the Beck 36x for the same application.

For my other applications, I want the angle to be as high as possible. the Headlight COB seems to fit this bill well for the 20XMM, and indeed I now have one 20XMM with the Angel Eye COB mounted, and a second 20XMM with the Headlight COB mounted! The Headlight COB ID is slightly smaller than the front element but it does not seem to compromise performance.

What I believe I need is a COB ringlight that has an ID of ~13-14mm with OD of 18-20mm, basically a 20mm Angel Eye (or AliExpress type). This would work for the Beck 36x with the nose piece in place and offer the correct lighting angle.

I may be able to modify an UltraFire to do this, but have been hesitant since they are not readily available. If all else fails I may need to try it.

mawyatt · Post by **mawyatt** » Fri Sep 20, 2019 3:41 pm

Interesting.

How do you mount these?

Best,

ray_parkhurst · Post by **ray_parkhurst** » Fri Sep 20, 2019 5:11 pm

mawyatt wrote:Interesting.

How do you mount these?

Best,

3M mounting tape.

Edited to add:

Here are (bad) pics of the two 20XMMs. Headlight COB on left, 40mm Angel Eyes on the right.

And here's another bad pic showing the mounting of the Headlight COB. Angel Eyes is similar:

dolmadis · Post by **dolmadis** » Tue Oct 01, 2019 8:57 pm

grgh wrote:Be interesting to see how you get on with that feedback,
looks ok but ill pass.

Just arrived....................

John

ray_parkhurst · Post by **ray_parkhurst** » Wed Oct 02, 2019 2:26 pm

dolmadis wrote:
grgh wrote:Be interesting to see how you get on with that feedback,
looks ok but ill pass.
Just arrived....................

John

I'm still waiting for the AliExpress 30mm COBs.

Any feedback so far on the headlamp types? I ended up purchasing a few different types on eBay that looked to have a variety of COB diameters and such, but turns out they all use the same COB. So I have ~12 of them in various case types! Some are actually quite nice headlamps, while others are very cheap and low quality, but they all use the same COB type.

Miljenko · Post by **Miljenko** » Mon Oct 14, 2019 11:32 am

Here is another one, just arrived today in a form of carabiner keychain flashlight. Built-in cob element has 23mm o.d and 12mm i.d., sounded great for microscope objectives lighting. Although there are 6 LED elements only, they emit huge amount of nicely spread light, drawing 0.53A at full power or 0.125A at lower power setting from 2 x CR2032 batteries (6V total). Quality of light seems to be pretty balanced and measures 6050K. And all of that for less than $2, including batteries. So far only the good news.

But here comes the bad news: central part of the printed circuit board with the on/off/mode switch can't be cut out in order for the lens to peek through. There are circuit traces on both sides that can't be reconected if cut out. Or somebody very skilful with soldering iron might do the trick?
For those, here is the Ebay link: https://www.ebay.com/itm/Waterproof-por ... 7qYAd0DNVg

ray_parkhurst · Post by **ray_parkhurst** » Mon Oct 14, 2019 1:08 pm

It's a nice, really small looking ringlight. might be possible to modify it to work with a hole in it. I may pick one up and give it a try...

Miljenko · Post by **Miljenko** » Tue Oct 15, 2019 11:49 am

Another pleasant surprise today from my postman: 30, 40 and 45mm COB ring lights arrived so I immediately did (guess what) measuring and testing!

They contain 16, 20 and 24 led elements behind layer of phosphor. I measured 5600K with slight tint shift to +15. Color accuracy is not very close to daylight or even flash light but no colors are missing. Both Delta C and Delta E color errors are acceptable:

And here are dimensions I measured on all three rings. The smallest dimension, alu plate i.d. can be easily enlarged to COB i.d. with Dremel or round file.

So far so good. But here comes the ugly part: only the smallest COB ring is properly designed concerning the max permissible dissipation. When connected to 12.0V power supply it draws 0.23A so dissipation is within 3W specs and temperature raise is acceptable. This is not the case with 40 and 45mm rings: the larger stays close to 0.5A absorbing 6W which is above rated power (5W) and heat buildup is excessive. Inserting 1 ohm resistor in series cuts the current to acceptable 350 - 400mA. Much worse situation appears with 40mm unit which starts at 0.5A when cold but very soon gets over 0.6A because of led negative temperature coefficient. Of course, I didn't wait to see how far would it go but such excessive current would soon bring the light to burnout. I suggest adding 2.2 ohm resistor in series which cuts max current to below safe 300mA limit. I'm having high hopes for those ring lights combined with ping pong ball halfs and varios LED bulb dispersion domes.

viktor j nilsson · Post by **viktor j nilsson** » Tue Oct 15, 2019 12:02 pm

Why don't you run them using a constant current power supply? I thought most LEDs behaved that way when fed a constant (high-ish) voltage.

Miljenko · Post by **Miljenko** » Tue Oct 15, 2019 12:15 pm

Because those do have internal current limiting resistors which work ok when properly calculated and manufactured. Stable voltage power supply plus precise resistor are usually precise enough to keep leds within permissible dissipation.
In this case, obviously only 30mm units are properly tailored. Missdesigned led bulbs are very common practice with Chinese manufacturers. I have whitnessed dozens of dead led bulbs on my car so I eventually gave up and switched to established bulb manufacturers!

mawyatt · Post by **mawyatt** » Tue Oct 15, 2019 12:34 pm

Hi Mike,

I agree with Viktor, run these LEDs with a CC source and you can regulate the current without fiddling with resistors. The negative (or positive) TC won't affect your results either.

I just got a cheap eBay supply for $35 to supplement my older lab supply. This has CC and CV with 5A and 30V max output.

https://www.ebay.com/itm/30V-5A-DC-Powe ... 2749.l2649

BTW these Circular LEDs do look interesting, I'll probably play with some after I get my Precision Piezo Stage Controller wrapped up, hopefully soon!

If you need a CC source for your use with your setup, let me know I'll design one for you (have all parts also).

Best,