# Would I get a better lumen output and improved thermal characteristics for the same wattage if I get a higher rated LED? [closed]

I'm planning on building a bright DIY high CRI LED video/photo floodlight out of the following components and considerations:

• High-power Neutral White (4000K?) LED rated at 95 CRI
• No add-on lens so I get the most uniform and wide-angled light output
• ARCTIC Alpine 11 Passive (capable of passively cooling Intel CPUs up to 47 watts)
• Boost/step-up converter with current-limiting ability
• Miniature wattage meter (maybe)
• An target maximum drive power target of ~40W

I don't know what thermal adhesive to get yet for the most ideal thermal conductivity, whether that'd be a one-piece silicone based, a two-piece Arctic Silver, or something similar.

My LED Chip research has been done exclusively on Cree LEDs and I'm confident that they are the best brand for me to go with, but I'm open to other suggestions if there are any.

I've narrowed down my options to these:

CMA:

• CMA1516-0000-000N0Z0AL5A (41W)
• CMA1825-0000-000N0Z0AL5A (61W)
• CMA1840-0000-000N0Z0AL5A (87W)

CMT:

• CMT1420-0000-000N0Z0AL5A (49W)
• CMT1922-0000-000N0Z0AL5A (57W)
• CMT1925-0000-000N0Z0AL5A (64W)
• CMT1930-0000-000N0Z0AL5A (77W)

From what I see, their CMA series LEDs were released in Q4 2017 while their CMT series came out in Q1 2018. I'm leaning more toward a CMT chip considering their prices are about the same while having potentially better lumen density and efficiency characteristics (I'm not entirely sure though).

How will a higher wattage LED driven at 40W scale in terms of lumens, thermals and heat tolerance/durability? Does CPU TDP-dissipation apply equally to heat-dissipation of an LED?

• What is your goal? High powered LED's for the sake of high power, or high efficiency LED's that are super bright at low power levels? They also have a narrow field of view which greatly increases brightness down the center. Great for spotlights and flashlights, but too harsh for a reading light. If going for high power consider a copper mounting plate. Copper is 83% more efficient at heat transfer than aluminum. – user105652 Nov 14 '18 at 4:32
• @Sparky256 Heck with copper. Natural diamond is 5.5 times more conductive than copper. And CVD is perhaps 6 times more conductive. I'd go for the CVD mounting plate every time. ;) There is the problem of mounting to it with any chance of using anywhere near all that capacity, though. – jonk Nov 14 '18 at 5:30
• @Sparky256 My goal is have a low-cost yet high quality adjustable light for photography and the occasional videography, I just want it to be optimized to make the most of 40W for those times I'd need it. My constraint is in place to ensure compatibility with that heatsink (assuming my TDP theory is correct) and allow it to be occasionally powered by a portable 12V battery pack. And yes, 40W will more than likely be overkill in most cases – user3125996 Nov 14 '18 at 5:38
• @junk I know about diamond having the best natural heat transfer, but did not think the OP would buy into that... – user105652 Nov 14 '18 at 5:38
• So three of the cheap LED 12W temperature/lumen adjustable LED floodlight panels from eBay are not good enough? – Dirk Bruere Nov 14 '18 at 15:22

Would I get a better lumen output and improved thermal characteristics for the same wattage if I get a higher rated LED?

The cost of thermal management is high for CoBs. More and lower wattage LEDs are usually most efficient. Efficacy usually drops when you exceed the "test current".

What I do is implement the best thermal management I can do then adjust the current so the PCB temperature next to the LED is 40°-50°C.

One of the most important characteristics is the efficacy specified in Lumens/Watt. Higher efficacy means more light, less heat.

Cree LEDs and I'm confident that they are the best brand for me to go with

Too general. Cree makes very good LEDs. Citizen, Samsumg, Lumileds, Luminus, and Bridgelux make very good LEDs also.

the most uniform and wide-angled light output

CoBs will have the least uniformity due to the high lumen density. They generally have the least lumen/watt efficacy.

A strip of LEDs will give best uniformity. Mid-power LEDs have the best efficacy.

I am not well versed on LEDs for photography regarding CCT and CRI. I do know higher CRI is more natural. I mention this because the strips I would be interested in if I were looking for photography lighting are 90 CRI.

I am thinking that a variety of CCTs would be desirable. And a tunable CCT would be a big plus. Dial in the mood.

The Bridgelux Vesta Series Tunable White Linear Strips are very reasonably priced and versatile. Each strip has two rows of mid-powered LEDs. One row of 2700K and one row of 5000K. You can use two LED drivers, one for each row, and "tune" the CCT in any combination.

The higher CRI is difficult to achieve as it requires more red than most LEDs can produce. White LEDs use phosphor wavelength converters to convert 450 nm deep blue (near black light) to blue, green, yellow, orange and red. Red being the least efficient.

If we look at the spectrum for a 4000K we can see the amount of red and its peak wavelength.

Notice the "Premium Color" peak wavelength is 630 nm and the 90 CRI peak is about 615 nm. 615 nm is a red-orange.

Cree CMT1922

Notice the 2700K 90 CRI red peak is 630 nm.

Bridgelux Vesta

ARCTIC Alpine 11 Passive

With strips thermal management is much easier as the heat is distributed over a larger area and the efficacy is better. You would need a heatsink only if you were pushing both rows hard.

If I were to use a heatsink with these strips I'd use a $5 HeasinkUSA's 12.000" Wide Extruded Aluminum Heatsink cut to 1". I would apply it using the thinnest 3M thermal tape I could find. Vesta vs. Cree CMT1922 500 mA vs. 600 mA 25V vs. 34V 24W vs. 20W 3272 lm vs. 2385 lm 136 vs. 116 lm/W$5 vs. \$8

You need a high quality LED driver if you are going to use these for video. You need continuous conduction with low ripple current.

I would use two (one for 2700K and one for 5000K) Mean Well HLG-60H-C700B drivers (5% ripple current). I would drive two BXEB-TL-2750G-1000-A-13 in series.

I would mount the strips about 6-8 inches apart for best uniformity.

I used seven strips mounted on aluminum angle brackets.

I made a PCB for power distribution and use a dip switch to select currents. The Mean Well HGL type B can use resistors to set the current. I have a pot to fine tune.

CRI does make a difference

My goal is have a low-cost yet high quality adjustable light for photography and the occasional videography,

Short-life high-power incandescent bulb. Or use a standard bulb and overvoltage it.

The light is for sure better than that from any LED, CFL or similar. The only thing even cheaper and also much much better is a reflector panel for sunlight. And sunlight. It's free.

All LEDs have reduced luminous efficacy at high temperatures. A higher rated LED may have lower $$\\theta_{JC}\$$ allowing you to run it at a lower junction temperature for the same heat sink and ambient temperature.