How do they do it? (adjust light output)

UFO

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I looked for a thread on this but was unsuccessful, so I hope you don't mind if this has been asked before.

LED Brightness: How do manufacturers "make" a flashlight burn at a specific brightness level?

What I mean is, if my flashlight has a Lumen rating of 750, how do companies "make" the bulb/diode burn at that level? Do they use specific bulbs or is there some type of regulator that drives power from the battery to make it burn at that specific setting?

I would liken this to BHP on a car. I have a basic understanding on how they make an engine that will produce 450 BHP, but don't understand the electronics part for the flashlight. Does this make any sense?
 

bykfixer

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Re: How do they do it?

Well, since you mention engines the LED is like an engine. Matter of fact it is even referred to as engine at times. But like an engine has to be assembled to work the LED engine is similar. As in it's not just a chip hooked to a battery but there are parts that are assembled and when electricity is applied a chemical reaction occurs within the LED that causes it to glow. Some add turbo too.

Others can elaborate or correct me where I went wrong.
 

idleprocess

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Re: How do they do it?

Disclaimer: I am by no mean an electrical engineer

Short answer
Pick a LED for your application that best hits your desired output - and other requirements - then control the drive current to hit your desired lumen output, adjusting for factors that reduce LED output or reduce net light output.

Long answer
Let's say you've picked the Cree XHP50.3 (3.0V) LED 5000K, 80CRI. Looking at the spec sheet, some basic facts emerge: maximum drive current (If) of 6A, 3.1V max forward voltage (Vf) at 2.8A If, maximum junction temperature 150C (pg 3), typical lumens 1040 @ 85C / 2.8A If (pg 10).

Let's say we're trying to achieve about 1500 lumens. We'll fudge the math a little and say that's 150% of of our baseline 1040 lumens. Page 20 shows our output vs current curve - looks like about 4.75A. But we know that we're going to produce heat in the process - especially driving the LED so hard. Thus we need to consider page 18 - relative flux vs junction temperature and evaluate what our physical design parameters are - how much heat management does our design have and do we intend to run 1500 lumens indefinitely? Knowing the overall thermal resistance will determine how long the light can operate at 1500 lumens as well as how much you'll need to adjust the drive current to compensate for output sag.

Another factor to consider is optical loss. A typical reflector + lens combination will subtract something like a third of output; an excellent combination will cut that closer to 10%. Thus, you'll need to adjust drive current up to achieve your desired level of output to compensate for light loss.
 

UFO

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Re: How do they do it?

Wow. That sounds like a very technical process. I wasn't aware of all the details, (Math) needed to produce a quality light. Many things to consider. Thank you both for your detailed answers. I'm starting to understand how this works now. Many thanks.
 

idleprocess

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Re: How do they do it?

Wow. That sounds like a very technical process. I wasn't aware of all the details, (Math) needed to produce a quality light. Many things to consider. Thank you both for your detailed answers. I'm starting to understand how this works now. Many thanks.

Yup.

Dishonest companies will quote values off the LED spec sheet that may or may not have anything to do with how the light internals operate even on a bench with no optical losses and infinite cooling. More honest companies will see something close to their claimed output at switch-on for a second or two with fresh cells and the light at ambient temperatures. Honest manufacturers will quote actual output values under real-world conditions.

Take a guess how the claimed output values stack up, high to low.
 

UFO

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Re: How do they do it?

Take a guess how the claimed output values stack up, high to low.[/QUOTE]

I'm not sure I understand.
 

idleprocess

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Re: How do they do it?

Take a guess how the claimed output values stack up, high to low.

I'm not sure I understand.

They will be in descending order. The "spec sheet value" claim accounts for nothing that cuts output in reality and will be highest (this is typical of no-name brands on the 'Bay and the 'Zon). The "gamed testing" regime will be in the middle since it will at least account for optical losses (companies that adhere to the FL1 Standard are generally within this bracket). The final regime will be the lowest since it will be real-world measurement that accounts for all routine factors (there are few within this space since they cannot compete on lumens claims).
 

KITROBASKIN

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Re: How do they do it?

How do manufacturers "make" a flashlight burn at a specific brightness level?

Seems like HDS is the only maker that does this, right?
(Probably) Everyone else decides to use some emitter with a fuel source, body, and electronics then hopefully engineers it with a mind towards efficiency but most likely looks to see how much it will cost to fabricate in a heavily competitive market, seems like. Then the marketing people use words and pictures to make it sell as much as possible.

Hopefully another member will elaborate, possibly describing how HDS works.

On a side note; here's hoping we get a more specific title to a thread next time, rather than "Gee Whiz This Is Something"
 
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archimedes

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I looked for a thread on this but was unsuccessful, so I hope you don't mind if this has been asked before.

LED Brightness: How do manufacturers "make" a flashlight burn at a specific brightness level?

What I mean is, if my flashlight has a Lumen rating of 750, how do companies "make" the bulb/diode burn at that level? Do they use specific bulbs or is there some type of regulator that drives power from the battery to make it burn at that specific setting? ....

Yes ... so I've moved this to the Flashlight Electronics subforum for you...

.... On a side note; here's hoping we get a more specific title to a thread next time, rather than "Gee Whiz This Is Something"

... and added a more helpful title[emoji106]
 
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UFO

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Re: How do they do it?

They will be in descending order. The "spec sheet value" claim accounts for nothing that cuts output in reality and will be highest (this is typical of no-name brands on the 'Bay and the 'Zon). The "gamed testing" regime will be in the middle since it will at least account for optical losses (companies that adhere to the FL1 Standard are generally within this bracket). The final regime will be the lowest since it will be real-world measurement that accounts for all routine factors (there are few within this space since they cannot compete on lumens claims).
Thank you idleprocess. This information is very helpful. I think I would equate this measurement system to stated MPG ratings on new cars. In a perfect world, the car will get 32 MPG. In the real world it's more like 24. I appreciate you taking the time to explain this in a language I can understand. Many thanks.

UFO
 

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