Been reading a bit on de-doming and from what I read, it tightens the beam angle, it reduces the flood angle by about 13 degrees.
But I thought I also read de doming was done to make a wider flood.
What am I missing here?
dedoming also warms up the LED tint color (usually)
I have no experience in dedoming any cree led but I’ve experimented with flat chinese LEDs by dropping water droplets on the LED and always turns the tint cooler
I’ve never heard dedoming widens the flood
Yes, that is what I had read,
Colour temp is of no great worry. I am not after any perfect or matched colour rendition.
Simple explanation,
Dedoming widens the spread of light from the emitter, when using a reflector this means more light hits the reflector and is thrown forward, so more lumins out of the front and less to the side of the light.
Overall you lose lumens, but if you want max throw and not worried about spill, dedoming is the way to go.
Cheers David
From TEEJ:
Throw is mostly a function of putting as much lux as possible on a distant target…and that means lumens per square meter, or, more simply, the most lumens possible on the smallest area possible.
To focus a beam, ideally, it would be a “point source”, a single point, so that the collimation would be theoretically perfect…all the “rays” from one point WOULD focus right where you want them.
So far at least, we have no devices that emit light from a single point…even a laser beam has 3 dimensions.
So, the compromise is to make the “point source” as small as possible…so more of what is emitted can be focused BETTER.
The dome over an LED magnifies the emitter if you look down into your light. A magnified image looks larger, so, it makes the apparent emitter surface look larger, and, therefore, have less of a tight focus (A larger source).
When you remove the dome, the system “sees” a smaller emitter, and, therefore, throws what is emitted farther.
So, for a given LED, dedoming it, or making it w/o a dome, etc, produces a smaller source which can be focused tighter and produce more throw.
The dome, which magnified the LED, improved the lumen output, but not necessarily the hot spot output more than the corona out put, etc…typically, it made the corona or hot spot fatter. (The same light across a fatter area is less intense)
IE: A “normal” beam has a central hot spot (The ONLY part measured when looking at “throw”), a donut of somewhat dimmer light around the hotspot, called the corona, and, light that missed the reflector/focus system altogether, called spill (It spills out, unfocused…).
The dome is a way to control the relative size and lumen distribution in the 3 above parts of the beam. Removing it changes that proportion, typically stealing some corona and adding it to the hotspot.
So, if the light normally used a dome and produced a total of 1,000 L OTF, for example, maybe 40% of that was hotspot, 50% was corona and 10% was spill. That means the throw is limited to ~ 400 L of the total.
If dedomed, it might take another 400 L or so from the corona, and maybe some of the splill, and about double the lumens now going into the throw.
If you remember that throw is in lux, and lux is lumens per square meter, doubling the lumens doubles the lux right off the bat.
So, dedoming can often double the lumens re-proportioned into the throw, by emitting them from a smaller surface area for the system to focus…so it focuses more light into the hot spot, where its thrown. It can also make the hot spot smaller, which means the same lumens are now concentrated into a smaller area, which is more intense (More lux).
Some people lock into “smaller emitter = more throw”, and forget that a larger emitter, if producing more lumens per square millimeter of that LED, can out throw the smaller emitter…as its getting its concentration of lumens higher by simply making more of them than the smaller emitter can.
So, depending on what’s focusing the light, while a smaller emitter/de-domed emitter will have more throw all else being equal….all else are not always equal.
The other issue is tint shift….which touches on another aspect of the dome, which is that the dome has a refractive index and will tend to have an impact on the light shined through it. When you remove the dome, you remove whatever that influence was.
In MOST cases, the dome made the light passing through it less warm…so, removing the dome allows the removed warmth to remain, so, the beam tends to get warmer in tint when dedomed.
1 Thank
It does neither widen nor narrow the beam of the LED itself significantly.
It reduces the total output (luminous flux) a bit, since the dome helps to get the light out of the die.
However that reduced output is coming from a smaller apparent area (since the dome created a magnified image of the die), so the illuminance (surface brightness, some kind of brightness density) is higher, and that allows a more intense focusing of the beam with a reflector or lens, thus gives a narrower beam with more luminous intensity (candela) and throw.
Edit: I'm afraid that TEEJ quote has some flaws.
It sounds like the issue of if the de doming increases or decreases the emitted light angle is one now one is sure of.
I have definitely seen it written in another post or write up on how to de-dome, that removing the dome decreases the angle of the light emitted by 13 degrees. I am still confused by how removing the dome decreases lumen output, It may alter its angle of emittance, but removing something that is in the light path, effectively blocking some lumens, I can’t see how it decreases lumens by removing it.
I can see that by removing the dome, I can get a lens closer to the emitter surface. Maybe that explains the greater angle output.
But if it works and I can get a wider beam by de doming and getting the lens closer then it has to be worth a shot.
Thanks
…but one thing I’ve learned on here about LED domes: The phosphor layer tends to have some amount of total internal reflection. The index of refraction of the dome is somewhere between that of the phosphor and of the air, so it allows more of the light to escape. The LED is usually a blue emitter, and the phosphor layer is yellow. Together, they make a white light. In order to make the light white, some of the blue still has to come through. By staying inside longer, more of the blue is made into yellow before exiting in a de-domed emitter. That’s why the tint is warmer. This is all very simplified and maybe not exactly how it all works together, but close enough.
The photo in the op of this thread shows a good side-by-side comparison of domed/dedomed in a reflectored light.