Thinking of a new light ..
- Thread starter stardustsailor
- Start date
stardustsailor
Well-Known Member
Probably yes ....
But I'm afraid of the "sticky" smoke residues ,fuming onto the silicone LES of CXAs ,to try it ...
But I'm afraid of the "sticky" smoke residues ,fuming onto the silicone LES of CXAs ,to try it ...
Last edited:
stardustsailor
Well-Known Member
Nope ...
I did not notice anything like that ....
stardustsailor
Well-Known Member
....Hm...No electronics smell like vacuum tubes? I love that smell
Well...
The bakelite tube sockets heating up ...
The dust on the tubes ,heating up ...
The oily/greasy/waxy linen paper used as ...pcb ...
Yeap...
Nice smells of the past ...
Sometimes ,still there in an old 'forgotten' Mesa ,Orange or Marshall..
Or in an old ,'grannie's' radio ....
" Leftovers " ...
..
Reminders ...
hm...
Yeah...
..
stardustsailor
Well-Known Member
...And in some forgotten Fenders ...Yes ..LOL ...
guod
Well-Known Member
http://www.advancedaquarist.com/2014/4/lighting? utm_source=nivoslider&utm_medium=slider&utm_campaign=clickthru
posting this in COBLAND, hmm....maybe not my best idea.
stardustsailor
Well-Known Member
On the contrary Guod.
Very good idea.
(Sometimes is needed a rather 'rough' landing ! ...LOL ... )
Very informative article ...
Still,there's one thing that is not quite clear to me ,even after reading this article ...
Ok ...
If indeed "Even Cree declares about 34% less efficiency for their best COBs today, compared with individual LEDs. "
How come Cree claims that CXA COBs are the most efficient of all the rest phosphor conversion whites ?
(At least regarding the 'top bins " of CXA series ...)
Isn't that kinda weird ?
Anyway ...
It really has gotten my attention ,the 'algae' thing and the 660 nm reds ...
Myself I've noticed something that might have a relation to that ...
Since I was using the Oslons 660 nm ,I've noticed (most of times ) a thin ,green (lime bright green )
' layer ' of some sort ..(looked really something like algae ...) ..on top of the soil ..(peat-perlite ,actually ..),
specially when canopy was not large enough ,to 'shade' the pot soil ....
And I've always wondered ,if that can be harmful to the plants ..
(Although ,it seemed not to affect plant growth or harming directly the plant itself...)
Maybe algae formation on top-soil ,isn't that 'dangerous' like if formed in aquatic environments ..
(like aquariums or hydroponics ...There ,I think can be devastating ..)
Great and very informative article.
Don't have much time ,right now ,to look it through ,more carefully ,but it's put on 'favourites' to be studied later .
Nice find ,Guod !
Cheers !
stardustsailor
Well-Known Member
Guod...
....
Something else ....
I've found an old CRT tv at the 'recycle trash bin' ....
'LOEWE '
......
Quite old ..(looks from late 70's / early 80's ... ) ...
Inside ...( I gutted it ,'in situ' ...) ..WoW !!!
Every single component is of highest quality ! ...
Lots of WIMA (red and light blue ones ) caps !!!
Are they worthy ?
I mean ,is it worthy to spend sometime and unsolder them one by one ?
Does age affect those caps ?
Can they be re-used ?
(Without great failure risk,I mean ...)
(I'm pretty amazed ..
I do not see that often so high quality of components !
No matter if of-quite- older tech ...)
....
Something else ....
I've found an old CRT tv at the 'recycle trash bin' ....
'LOEWE '
......
Quite old ..(looks from late 70's / early 80's ... ) ...
Inside ...( I gutted it ,'in situ' ...) ..WoW !!!
Every single component is of highest quality ! ...
Lots of WIMA (red and light blue ones ) caps !!!
Are they worthy ?
I mean ,is it worthy to spend sometime and unsolder them one by one ?
Does age affect those caps ?
Can they be re-used ?
(Without great failure risk,I mean ...)
(I'm pretty amazed ..
I do not see that often so high quality of components !
No matter if of-quite- older tech ...)
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PSUAGRO.
Well-Known Member
Uh oh........thanks for raining on our parade
stardustsailor
Well-Known Member
Fault #1 :
(...)A shorter thermal path in COBs is usually listed as an advantage(=>Fault #3), however, this is not as simple as it seems. As an example, let us consider Cree’s newest COBs. As one of World’s top leaders in LED technologies, this company pays closest attention to improving the thermal characteristics of their products. According to the datasheets, thermal resistance of Cree’s COBs varies from 2.5°C/W for CXA1507 to an impressive 0.8°C/W for CXA2530.
Seems to be pretty good, huh? Only until we notice that, say, CXA2520 may consume up to 50W of power. According to the datasheet (see the picture below), this will add a significant 40С to junction temperature above the temperature of the LED case.
For CXA2530, with 61W power consumption, junction temperature will be even higher.(...)
(And for CXA3070 ,even higher ,I may add ... )
Anyway ...
I'm for sure, not good at math ...
And I'm an 'underground' stoner-grower ,not an 'exceptional' fish-watcher-breeder ...
But hey ...
WTF ?
What kind of math is this ?
50 Watt x 0.8 °C /Watt = 40°C ....
At Tc=85°C ,Vf of CXA2520 is 40 VDC ,when If =1250 mA .
Total electrical power = 50 Watts .
I 'm not aware of the exact efficiency of this case ,but I roughly guess that it is around ~30% ...
30% of the 50 Watts are light ....
70 % of 50 Watts are heat .
.7 * 50 = 35
35 Watts of heat * 0.8 °C /Watt( of heat ) = 28°C
85+28=113 °C
Tj =113 °C
And that's about the max operating limit Cree suggests ,anyway ....
I do not see any 'case' made against the 'thermal path /resistance ' of COBS vs 'individual crystals ' ..
Absolutely none .
(...)A shorter thermal path in COBs is usually listed as an advantage(=>Fault #3), however, this is not as simple as it seems. As an example, let us consider Cree’s newest COBs. As one of World’s top leaders in LED technologies, this company pays closest attention to improving the thermal characteristics of their products. According to the datasheets, thermal resistance of Cree’s COBs varies from 2.5°C/W for CXA1507 to an impressive 0.8°C/W for CXA2530.
Seems to be pretty good, huh? Only until we notice that, say, CXA2520 may consume up to 50W of power. According to the datasheet (see the picture below), this will add a significant 40С to junction temperature above the temperature of the LED case.
For CXA2530, with 61W power consumption, junction temperature will be even higher.(...)
(And for CXA3070 ,even higher ,I may add ... )
Anyway ...
I'm for sure, not good at math ...
And I'm an 'underground' stoner-grower ,not an 'exceptional' fish-watcher-breeder ...
But hey ...
WTF ?
What kind of math is this ?
50 Watt x 0.8 °C /Watt = 40°C ....
At Tc=85°C ,Vf of CXA2520 is 40 VDC ,when If =1250 mA .
Total electrical power = 50 Watts .
I 'm not aware of the exact efficiency of this case ,but I roughly guess that it is around ~30% ...
30% of the 50 Watts are light ....
70 % of 50 Watts are heat .
.7 * 50 = 35
35 Watts of heat * 0.8 °C /Watt( of heat ) = 28°C
85+28=113 °C
Tj =113 °C
And that's about the max operating limit Cree suggests ,anyway ....
I do not see any 'case' made against the 'thermal path /resistance ' of COBS vs 'individual crystals ' ..
Absolutely none .
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stardustsailor
Well-Known Member
Fault #2 :
(...)
A better approach would be, instead of COBs, to use carefully selected individual LED emitters (the ones with most efficient bins, to minimize heat generation), then mounted on an advanced MCPCB to provide the best heat dissipation from the crystal. This can yield less than a 10°C temperature difference between the junction and the MCPCB, and about 12°C between junction and heatsink (see our thermal vision study, Fig 9).
Therefore, we believe that the best approach to avoid the Disco effect is through the use of individual LEDs packed tightly on a custom MCPCB. This way the light beams from differently colored LEDs will mix up well, without forming color shadows. The smaller is the distance between individual LEDs, and the better it will be able to overcome the color shade effect.
The distance between individual LEDs, however, cannot be smaller than the size of secondary optics. Fortunately, compact and efficient LED lenses are available today. The best effect is achieved through the use of hybrid optics, combining a TIR lens and a special light diffusing material.
Challenge number two: Battling the heat
Modern LEDs are quite efficient at the conversion of electric energy into light. However, even the most efficient LEDs today waste about half of the consumed energy in the form of heat. Since the crystal is quite small (a power LED’s crystal usually has the surface of only 1-2mm2 or 0.0015-0.003in2), its generated heat density is quite large. In fact, it is about 30 times as large as the heat density through the soleplate of a household iron! (...)
..........................................................................................
a)
Oslon SSL (total and not only the pads !! ) case bottom surface : 3.1 mm x 3.1 mm = 9.61 mm^2 ....
to dissipate ~1.5 Watt of heat (maxed out )....
Available heat conducting surface area per watt of heat : 9.61 / 1.5 =6.4 mm^2 / Watt
CXA3070 case bottom surface: 27.3 x 27.3 = 745,3 mm^2....4
to dissipate ~60 Watts of heat (maxed out )
Available heat conducting surface area per watt of heat : 745.3 / 60 =12.42 mm^2 / Watt
Double available conducting area per watt of heat on a Cree CXA3070 COB versus an Osram Oslon SSL individual "crystal " ..From the smallest ones ..
To be easily packed tightly .......
To avoid disco effect ....
On a mcpcb ....!!!!!
( See next fault ...)
.....
b)
I want a thermal vision study of some COBs also ....
Cause this ,by itself ,ain't telling shit ...
Nothing to reference ,nothing to compare to ....
c)
Talking about light output efficiency ?
Light Diffusers....
????
Ok ......Later,this one ...
(...)
A better approach would be, instead of COBs, to use carefully selected individual LED emitters (the ones with most efficient bins, to minimize heat generation), then mounted on an advanced MCPCB to provide the best heat dissipation from the crystal. This can yield less than a 10°C temperature difference between the junction and the MCPCB, and about 12°C between junction and heatsink (see our thermal vision study, Fig 9).
Therefore, we believe that the best approach to avoid the Disco effect is through the use of individual LEDs packed tightly on a custom MCPCB. This way the light beams from differently colored LEDs will mix up well, without forming color shadows. The smaller is the distance between individual LEDs, and the better it will be able to overcome the color shade effect.
The distance between individual LEDs, however, cannot be smaller than the size of secondary optics. Fortunately, compact and efficient LED lenses are available today. The best effect is achieved through the use of hybrid optics, combining a TIR lens and a special light diffusing material.
Challenge number two: Battling the heat
Modern LEDs are quite efficient at the conversion of electric energy into light. However, even the most efficient LEDs today waste about half of the consumed energy in the form of heat. Since the crystal is quite small (a power LED’s crystal usually has the surface of only 1-2mm2 or 0.0015-0.003in2), its generated heat density is quite large. In fact, it is about 30 times as large as the heat density through the soleplate of a household iron! (...)
..........................................................................................
a)
Oslon SSL (total and not only the pads !! ) case bottom surface : 3.1 mm x 3.1 mm = 9.61 mm^2 ....
to dissipate ~1.5 Watt of heat (maxed out )....
Available heat conducting surface area per watt of heat : 9.61 / 1.5 =6.4 mm^2 / Watt
CXA3070 case bottom surface: 27.3 x 27.3 = 745,3 mm^2....4
to dissipate ~60 Watts of heat (maxed out )
Available heat conducting surface area per watt of heat : 745.3 / 60 =12.42 mm^2 / Watt
Double available conducting area per watt of heat on a Cree CXA3070 COB versus an Osram Oslon SSL individual "crystal " ..From the smallest ones ..
To be easily packed tightly .......
To avoid disco effect ....
On a mcpcb ....!!!!!
( See next fault ...)
.....b)
I want a thermal vision study of some COBs also ....
Cause this ,by itself ,ain't telling shit ...
Nothing to reference ,nothing to compare to ....
c)
Talking about light output efficiency ?
Light Diffusers....
????
Ok ...
...Later,this one ...
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stardustsailor
Well-Known Member
Fault #3:
(...)
Heat removal from LEDs is very important since their lifespan and performance depend on the operating temperature. When the temperature of the crystal increases from 25 to 100C the performance of the most heat tolerant LEDs (Luxeon Rebel ES royal blue) decreases by 10%. In the same time, less heat tolerant LEDs may lose up to 75% of their efficiency (Luxeon Rebel amber). This drop of efficiency is even more pronounced in cheap LEDs of Asian make.
Unfortunately, commonly known technologies today do not permit mounting the LED crystal directly on the heatsink. The crystal requires a special package, and its heat transferring capability is described by a parameter called thermal resistance, usually measured in the degrees of temperature increase per watt of generated heat (C/W). The thermal resistance of the best individual LEDs is about 2.5C/W today.
Let us consider the influence of thermal resistance on crystal temperature. Suppose we have two 3W LEDs of the latest-generation. Let us consider, for example, a violet LED Semileds N35L-U-A with a thermal resistance of 4.4C/W, and a Cree XP-E2 green LED with 15C/W thermal resistance. When operating at 700mA, the respective voltage drop will be, approximately, 3.3V and 3.5V, and hence their overall power consumption will be around 2.31W and 2.45W respectively. In the first case, the LED package will add 2.31*4.4=10.16С to crystal temperature, and in the second case the temperature difference is much higher: 2.45*15=36.75С.
We need to supply current to the LED and the conductors should be somehow isolated from the heatsink. Therefore, the LED emitter is first installed onto a special PCB, which is then mounted on the heatsink. Thermal resistance of least expensive PCBs can be as high as 60C/W or more (see the datasheet for Cree XLamp _PCB_Thermal.pdf). This, however, is quite unacceptable, and therefore special metal PCBs (МСРСВs) have been developed. Their structure is shown in Fig 4:
You can see that the LED thermal pad does not touch the MCPCB metal directly, but through a thin dielectric layer. Unfortunately, thermal conductivity of dielectric materials is hundreds of times less than that of aluminum or copper, and МСРСВ’s total thermal resistance is somewhere between 0.2C/W (for LEDs with large surface area) and 5.3C/W for smaller crystals. Since we are planning to pack the LEDs tightly, in order to avoid the “Disco” effect, we shall assume a larger figure, towards 5C/W. This will add another 11.5С to 12.25С to the temperature of our crystals. These calculations are valid for a traditional MCPCB, but we can improve the situation significantly by using an advanced MCPCB like SinkPAD or similar.
The МСРСВ is not a part of the heatsink and is attached to it through a layer of heat conducting compound, which is required to fill in the gaps resulting from manufacturing imperfections of the attaching surfaces. The compound’s thermal resistance depends on material but, in any case, the thinner is the layer, the less will be the resistance. As a rough approximation, for a high-quality compound it is around 2C/W. This will add 4.6С and 5С respectively to our crystals.
Once the heat from the LED has reached the heatsink, it cannot be instantly transferred to the environment. A heatsink is usually selected in such a way that its average temperature would not exceed 50C when the surrounding air temperature is 25C. Heatsink temperature at the contact point with the МСРСВ will be around 60C. Thus, the crystals temperature will be 60+10.1+11.5+4.5=86.1С and 60+37.5+12.25+5=114.75С respectively. Note that if we attach such LEDs to a cheap FR-4 PCB with thermal resistance about 60C/W, crystal temperature may reach 252С. Since LEDs are attached with a solder which melts at about 217С, the LED would probably unsolder due to its own heat!
Note that our quoted 15C/W thermal resistance isn’t the worst case scenario: many Asian manufacturers avoid indicating this parameter in their datasheets, just because the figure is even worse. Also note that real-life temperatures will be worse than we calculated above, because of mounting imperfections of the МСРСВ, an uneven layer of the heat conductive compound, etc.
As we have seen, there are two main obstacles to removing excess heat from the LED crystal: the LED package and the MCPCB. Manufacturers are constantly working to overcome the first obstacle and the best LEDs on the market are using packages with reduced thermal resistance. Overcoming the second obstacle is more of a challenge since, until recently, there was no technology that would allow engineers to get rid of the dielectric layer between the LED thermal pad and the МСРСВ metal. In 2011, however, a US company SinkPAD (www.sinkpad.com) has offered a patented technology called SinkPADTM, allowing it to dissipate the heat from LEDs thermal pad directly to МСРСВ’s metal.
The structure of the SinkPAD МСРСВ is shown in Fig 5:
You can see the raised portions of the МСРСВ metal in the picture, which touch the LED’s thermal pad directly; whereas, the electric traces are situated on a separate PCB. This approach results in a significant reduction of thermal resistance, and the more LEDs there are on the MCPCB surface, the more pronounced is the effect. Therefore, this technology is preferred for our МСРСВ which will be densely populated with power LEDs. (...)
......
Heat path of a normal mcpcb / IMS pcb and individual led :
Semiconductor junction => led case => solder=> pad => TIM => alum/copper =>TIM =>heatsink
...............................................................
Heat path of a SinkPAD mcpcb and individual led :
Semiconductor junction(2.5C/W )=> led case( y area/Wheat ) => TIM => alum/copper =>TIM =>heatsink
vs
Heat path of a COB :
Semiconductor junction(0.8C/W ) => led case( 2*y area/Wheat ) => TIM =>heatsink
Rest my case ,here ...
(...)
Heat removal from LEDs is very important since their lifespan and performance depend on the operating temperature. When the temperature of the crystal increases from 25 to 100C the performance of the most heat tolerant LEDs (Luxeon Rebel ES royal blue) decreases by 10%. In the same time, less heat tolerant LEDs may lose up to 75% of their efficiency (Luxeon Rebel amber). This drop of efficiency is even more pronounced in cheap LEDs of Asian make.
Unfortunately, commonly known technologies today do not permit mounting the LED crystal directly on the heatsink.
The crystal requires a special package, and its heat transferring capability is described by a parameter called thermal resistance, usually measured in the degrees of temperature increase per watt of generated heat (C/W). The thermal resistance of the best individual LEDs is about 2.5C/W today.Let us consider the influence of thermal resistance on crystal temperature. Suppose we have two 3W LEDs of the latest-generation. Let us consider, for example, a violet LED Semileds N35L-U-A with a thermal resistance of 4.4C/W, and a Cree XP-E2 green LED with 15C/W thermal resistance. When operating at 700mA, the respective voltage drop will be, approximately, 3.3V and 3.5V, and hence their overall power consumption will be around 2.31W and 2.45W respectively. In the first case, the LED package will add 2.31*4.4=10.16С to crystal temperature, and in the second case the temperature difference is much higher: 2.45*15=36.75С.
We need to supply current to the LED and the conductors should be somehow isolated from the heatsink. Therefore, the LED emitter is first installed onto a special PCB, which is then mounted on the heatsink. Thermal resistance of least expensive PCBs can be as high as 60C/W or more (see the datasheet for Cree XLamp _PCB_Thermal.pdf). This, however, is quite unacceptable, and therefore special metal PCBs (МСРСВs) have been developed. Their structure is shown in Fig 4:
You can see that the LED thermal pad does not touch the MCPCB metal directly, but through a thin dielectric layer. Unfortunately, thermal conductivity of dielectric materials is hundreds of times less than that of aluminum or copper, and МСРСВ’s total thermal resistance is somewhere between 0.2C/W (for LEDs with large surface area) and 5.3C/W for smaller crystals. Since we are planning to pack the LEDs tightly, in order to avoid the “Disco” effect, we shall assume a larger figure, towards 5C/W. This will add another 11.5С to 12.25С to the temperature of our crystals. These calculations are valid for a traditional MCPCB, but we can improve the situation significantly by using an advanced MCPCB like SinkPAD or similar.
The МСРСВ is not a part of the heatsink and is attached to it through a layer of heat conducting compound, which is required to fill in the gaps resulting from manufacturing imperfections of the attaching surfaces. The compound’s thermal resistance depends on material but, in any case, the thinner is the layer, the less will be the resistance. As a rough approximation, for a high-quality compound it is around 2C/W. This will add 4.6С and 5С respectively to our crystals.
Once the heat from the LED has reached the heatsink, it cannot be instantly transferred to the environment. A heatsink is usually selected in such a way that its average temperature would not exceed 50C when the surrounding air temperature is 25C. Heatsink temperature at the contact point with the МСРСВ will be around 60C. Thus, the crystals temperature will be 60+10.1+11.5+4.5=86.1С and 60+37.5+12.25+5=114.75С respectively. Note that if we attach such LEDs to a cheap FR-4 PCB with thermal resistance about 60C/W, crystal temperature may reach 252С. Since LEDs are attached with a solder which melts at about 217С, the LED would probably unsolder due to its own heat!
Note that our quoted 15C/W thermal resistance isn’t the worst case scenario: many Asian manufacturers avoid indicating this parameter in their datasheets, just because the figure is even worse. Also note that real-life temperatures will be worse than we calculated above, because of mounting imperfections of the МСРСВ, an uneven layer of the heat conductive compound, etc.
As we have seen, there are two main obstacles to removing excess heat from the LED crystal: the LED package and the MCPCB. Manufacturers are constantly working to overcome the first obstacle and the best LEDs on the market are using packages with reduced thermal resistance. Overcoming the second obstacle is more of a challenge since, until recently, there was no technology that would allow engineers to get rid of the dielectric layer between the LED thermal pad and the МСРСВ metal. In 2011, however, a US company SinkPAD (www.sinkpad.com) has offered a patented technology called SinkPADTM, allowing it to dissipate the heat from LEDs thermal pad directly to МСРСВ’s metal.
The structure of the SinkPAD МСРСВ is shown in Fig 5:
You can see the raised portions of the МСРСВ metal in the picture, which touch the LED’s thermal pad directly; whereas, the electric traces are situated on a separate PCB. This approach results in a significant reduction of thermal resistance, and the more LEDs there are on the MCPCB surface, the more pronounced is the effect. Therefore, this technology is preferred for our МСРСВ which will be densely populated with power LEDs. (...)
......
Heat path of a normal mcpcb / IMS pcb and individual led :
Semiconductor junction => led case => solder=> pad => TIM => alum/copper =>TIM =>heatsink
...............................................................
Heat path of a SinkPAD mcpcb and individual led :
Semiconductor junction(2.5C/W )=> led case( y area/Wheat ) => TIM => alum/copper =>TIM =>heatsink
vs
Heat path of a COB :
Semiconductor junction(0.8C/W ) => led case( 2*y area/Wheat ) => TIM =>heatsink
Rest my case ,here ...
Last edited:
stardustsailor
Well-Known Member
To be honest and sincere ....
When I set route and start sailing to the Cobland ...
I had my doubts ..
I was pretty sceptical,about the whole 'voyage' ...
"Only warm white light ? "
"Yes ,at high irradiances " ..
" But so many diodes closely together ,under a silicone phosphor -doped 'disk' ? "
" Hot weather ! The climate there must be way hot ! ...."
Well ....
Ain't ...
I'm telling you ...
The surface is so large ,that heat conducts and is transferred way easy ...
I'm impressed as a DIYer !
The ' ease ' and 'flexibility ',the COBS offer is unmatched ...
A holder ,two screws and a tiny blob of thermal paste (TIM ) ...
These are the only things needed ,to install a COB in a heatsink !
POFC !
And as a led -grower ...
I'm also -so far- impressed !
The girl's flowering is just amazing !
(up till now,at least ... Still pretty early ,though,for 'final ' 'arguments' / 'claims' / 'results' )
...
I've been onto cheapo leds ,onto branded high quality leds and now at Cobland ..
I'm not planning to 'leave' soon ,from here ..
Amazing led "land " ...
Neither better or worse from individual leds ...
Just ..'different ' ...
In many of ways ...
Cheers .
When I set route and start sailing to the Cobland ...
I had my doubts ..
I was pretty sceptical,about the whole 'voyage' ...
"Only warm white light ? "
"Yes ,at high irradiances " ..
" But so many diodes closely together ,under a silicone phosphor -doped 'disk' ? "
" Hot weather ! The climate there must be way hot ! ...."
Well ....
Ain't ...
I'm telling you ...
The surface is so large ,that heat conducts and is transferred way easy ...
I'm impressed as a DIYer !
The ' ease ' and 'flexibility ',the COBS offer is unmatched ...
A holder ,two screws and a tiny blob of thermal paste (TIM ) ...
These are the only things needed ,to install a COB in a heatsink !
POFC !
And as a led -grower ...
I'm also -so far- impressed !
The girl's flowering is just amazing !
(up till now,at least ... Still pretty early ,though,for 'final ' 'arguments' / 'claims' / 'results' )
...
I've been onto cheapo leds ,onto branded high quality leds and now at Cobland ..
I'm not planning to 'leave' soon ,from here ..
Amazing led "land " ...
Neither better or worse from individual leds ...
Just ..'different ' ...
In many of ways ...
Cheers .
stardustsailor
Well-Known Member
.... efficiency ...
(...) Light Diffusers
We believe that proper light diffusers are very important part of a LED-based light fixture.
We applied serious efforts to address the “Disco effect” problem that was discussed earlier. We first tried to resolve the problem by designing a compact LED assembly with a very dense population of LEDs, each equipped with individual lenses[4]. Although the lenses helped significantly with the mixing of colors, the effect was not eliminated completely. Through extensive experimentation, we have found a suitable solution through the use of hybrid optical system.
The light from a densely populated LED assembly first passes through an efficient lens which is capable of concentrating about 93% of all emitted light into a narrow beam. This beam is then directed at a carefully selected light diffuser material which breaks it down into a very large number of smaller beams at slightly differing angles. These beams mix perfectly, forming an even distribution of all spectral components radiated by the LED assembly.
A microphotograph of the surface of the light diffusing material, designed by German Evonik specifically for color mixing purposes, is shown in Fig 12:
You can see on the photograph that the surface is not matte (or it would result in mere scattering and significant light loss), but consists of numerous chaotically distributed planes, providing perfect color mixing along with insignificant losses.
After passing through the diffuser, the beam becomes wider, and thus the LED fixture can be positioned comfortably at the height of 30-40cm (12-16 in) above water surface.
Our light diffusers are mounted in a ring which attaches tightly over the optics. Beside their main function, they also play another important role by protecting LEDs from particles of dust which are always present in the air and would gradually accumulate on the LED’s primary optics and the adjacent part of secondary optics. Initially, this dust is negligible, but over years of fixture’s operation primary optics will start absorbing light. This, in turn, would result in the overheating of the LEDs. The attached diffuser ring can be glued to the MCPCB, thus hermetically sealing the whole assembly, Fig 13. (...)
7% losses from concentrating lens .....
93% of radiant light is 'guided' in a 'diffuser '
Diffuser material properties :
85 % transmission* .....( 400-700 nm range aka ' visible' )
85 % of 93 % is ......
79.05 % of total radiant light power is transmitted ....
The 80%.....is left ...
-20% of light power ....
- 1/5 of total output is absorbed by the lens-diffuser combo ...
Efficiency ?
What ?
Watt / Watt ?
if (and only if ....) 40% total initial efficiency ,after lens-diffuser combo : 32 % ......
if (more realistic) 35% total initial efficiency ,after lens-diffuser combo : 28% ......
Same as a bunch of (selected out ? ) 'good' chinese 'cheapos' ....
Big deal ....
Cheers ..
*
Beer–Lambert law
In equation form,
where
is the intensity of the incident radiation and
is the intensity of the radiation coming out of the sample and
and
are transmittance and absorptance respectively. In these equations, scattering and reflection are considered to be close to zero or otherwise accounted for. The transmittance of a sample is sometimes given as a percentage.
(...) Light Diffusers
We believe that proper light diffusers are very important part of a LED-based light fixture.
We applied serious efforts to address the “Disco effect” problem that was discussed earlier. We first tried to resolve the problem by designing a compact LED assembly with a very dense population of LEDs, each equipped with individual lenses[4]. Although the lenses helped significantly with the mixing of colors, the effect was not eliminated completely. Through extensive experimentation, we have found a suitable solution through the use of hybrid optical system.
The light from a densely populated LED assembly first passes through an efficient lens which is capable of concentrating about 93% of all emitted light into a narrow beam. This beam is then directed at a carefully selected light diffuser material which breaks it down into a very large number of smaller beams at slightly differing angles. These beams mix perfectly, forming an even distribution of all spectral components radiated by the LED assembly.
A microphotograph of the surface of the light diffusing material, designed by German Evonik specifically for color mixing purposes, is shown in Fig 12:
You can see on the photograph that the surface is not matte (or it would result in mere scattering and significant light loss), but consists of numerous chaotically distributed planes, providing perfect color mixing along with insignificant losses.
After passing through the diffuser, the beam becomes wider, and thus the LED fixture can be positioned comfortably at the height of 30-40cm (12-16 in) above water surface.
Our light diffusers are mounted in a ring which attaches tightly over the optics. Beside their main function, they also play another important role by protecting LEDs from particles of dust which are always present in the air and would gradually accumulate on the LED’s primary optics and the adjacent part of secondary optics. Initially, this dust is negligible, but over years of fixture’s operation primary optics will start absorbing light. This, in turn, would result in the overheating of the LEDs. The attached diffuser ring can be glued to the MCPCB, thus hermetically sealing the whole assembly, Fig 13. (...)
7% losses from concentrating lens .....
93% of radiant light is 'guided' in a 'diffuser '
Diffuser material properties :
85 % transmission* .....( 400-700 nm range aka ' visible' )
85 % of 93 % is ......
79.05 % of total radiant light power is transmitted ....
The 80%.....is left ...
-20% of light power ....
- 1/5 of total output is absorbed by the lens-diffuser combo ...
Efficiency ?
What ?
Watt / Watt ?
if (and only if ....) 40% total initial efficiency ,after lens-diffuser combo : 32 % ......
if (more realistic) 35% total initial efficiency ,after lens-diffuser combo : 28% ......
Same as a bunch of (selected out ? ) 'good' chinese 'cheapos' ....
Big deal ....
Cheers ..
*
Beer–Lambert law
In equation form,
where
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stardustsailor
Well-Known Member
So long efficiency ...
One of my main concerns ,always there regarding individual monochromatic leds ,comes
from my 'belief' (more of a religion ,after all ? ) into ' full spectrum '...
.... white light ...
( 'Full spectrum ' ....Anyway ..It's a commonly used 'compromise ' term ,I guess .
To express/mean 'easily' the PAR/visible 400-700 nm E/M radiation wl range ...)
I've started in my first 'led world baby steps ' from/with monochromatics ...
Soon to realise their pros ..
Of their high efficiency ...
Of 'targeted' wls (desired in many of cases ) ...
And their cons ...
Very difficult to 'blend' the light ...( aka 'disco effect ' )
Plenty of electrical design difficulties due to different Vf / If ....
'Un -even efficiencies/ intensities ' made things ,even worse ...
( many reds vs few blues ...for example...
Blue are way powerful ...Underneath them, is way 'too much' ...
Away from them ,blue light disperses a lot ....
Way difficult to make light 'blend ' ...
Red light dominating parts at canopy here , blue light dominating spots there ... )
Plus ,the fact that in order to create 'a full ' white light from monochromatics ,they can
not just be used the red-green-blue ones ...The more wls the ..." better " ....
Regarding the quality of light ....only ...
Because the design and efficiency go to hell ........
Green / yellow / violet leds are way unefficient ...
If you add cyan ,amber ,FR ,UV ,etc ...
I just want to see how you're going to install /place all these and have a nice ,blended light ...
There's no -efficient -way ....
You can 've a blended light ,like those two aquarists ,but then ..efficiency suffers ,quite a lot ...
So ,what';s left ....?
Aaa!!!!!
Phosphor conversion whites ! (And quantum -dot ones ....Nowdays ! )
Ok ..
They are not (used to ......) so efficient like the monos ....
But ....
They have so muxh 'pros' to balance or even 'make up for' the efficiency losses due to
phosphor conversion losses & absorption ...
Way many 'pros' ,nowdays ...
Specially the COB tech ,gave a serious "kick" ,
a 'boost' in those desired characteristics of pc /qd
white leds ....
To some (like me ) they 've become 'one-way' ....
The only way ...
(At least for the moment being .........Until further notice ...LOL )
Cheers .
One of my main concerns ,always there regarding individual monochromatic leds ,comes
from my 'belief' (more of a religion ,after all ? ) into ' full spectrum '...
.... white light ...( 'Full spectrum ' ....Anyway ..It's a commonly used 'compromise ' term ,I guess .
To express/mean 'easily' the PAR/visible 400-700 nm E/M radiation wl range ...)
I've started in my first 'led world baby steps ' from/with monochromatics ...
Soon to realise their pros ..
Of their high efficiency ...
Of 'targeted' wls (desired in many of cases ) ...
And their cons ...
Very difficult to 'blend' the light ...( aka 'disco effect ' )
Plenty of electrical design difficulties due to different Vf / If ....
'Un -even efficiencies/ intensities ' made things ,even worse ...
( many reds vs few blues ...for example...
Blue are way powerful ...Underneath them, is way 'too much' ...
Away from them ,blue light disperses a lot ....
Way difficult to make light 'blend ' ...
Red light dominating parts at canopy here , blue light dominating spots there ... )
Plus ,the fact that in order to create 'a full ' white light from monochromatics ,they can
not just be used the red-green-blue ones ...The more wls the ..." better " ....
Regarding the quality of light ....only ...
Because the design and efficiency go to hell ...
.....Green / yellow / violet leds are way unefficient ...
If you add cyan ,amber ,FR ,UV ,etc ...
I just want to see how you're going to install /place all these and have a nice ,blended light ...
There's no -efficient -way ....
You can 've a blended light ,like those two aquarists ,but then ..efficiency suffers ,quite a lot ...
So ,what';s left ....?
Aaa!!!!!
Phosphor conversion whites ! (And quantum -dot ones ....Nowdays ! )
Ok ..
They are not (used to ...
...) so efficient like the monos ....But ....
They have so muxh 'pros' to balance or even 'make up for' the efficiency losses due to
phosphor conversion losses & absorption ...
Way many 'pros' ,nowdays ...
Specially the COB tech ,gave a serious "kick" ,
a 'boost' in those desired characteristics of pc /qd
white leds ....
To some (like me ) they 've become 'one-way' ....
The only way ...
(At least for the moment being .....
....Until further notice ...LOL )Cheers .
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PetFlora
Well-Known Member
Yeah, when I read the article the thing that jumped out at me was the MC. (In fairness the tech is moving at warp speed) Don't they know about the different voltages/heat? They did say they put something on the board so when individual diodes fail, they don't all turn off. HELLO. Also some o those will lose efficiency a lot sooner
But how about a bunch of 10-20w COBs spread out on a bar type heat sink with passive cooling?
But how about a bunch of 10-20w COBs spread out on a bar type heat sink with passive cooling?