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Old 12-17-2008, 01:20 AM #1
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Default Burning:  PHR-803T blu-ray vs LG 20x red

OK I've built two nice compact lasers so far, with the Viclight 3-AAA host & heatsink from Jayrob.
They work great, I'm really happy with them. I'm using Dr. Lava's FlexDrive v3 for both of them.

Blu-ray is running at 150mA.
Red is running at 420mA.

The blu-ray lights matches INSTANTLY, the same matches at the same distance with the red are rather difficult comparatively.

I guess I chalk it up to the differences in 405nm and 635/650nm light. I'm sure there are some physics that explain it.

Anyone care to elaborate a bit for me?

Thanks!


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Old 12-17-2008, 02:54 AM #2
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

The matches you have... do they have red tips?

I'll bet you if you take a black marker and color the tips of two matches, the red will light it faster... Problem with matches with red tips is that they absorb every color except red... They reflect red light, which is why they appear red to your eye. This also means most of your laser's energy is reflected off it rather than absorbed.
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Old 12-17-2008, 02:59 AM #3
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Aye, red ones and white ones. The blu-ray diode burns them both equally well.

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Old 12-17-2008, 06:59 AM #4
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

I got a box of matches that are multi color today, blue, yellow, green, purple, very odd. I hardly ever get red matches, normally brownish and all my strongest lasers light them instantly.
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Old 12-18-2008, 04:06 AM #5
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Keep in mind you have listed current to the LDs and not the power to them. The forward voltage of the Bluray is probably around double that of the red LD. That brings the power going into both a little closer. The rest can likely be explained by the ability to focus the beams and the energy absorption rate for the different light wavelengths.
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Old 12-18-2008, 11:53 AM #6
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

A red at 420 mA will still have more power than a bluray at 150, though the ratio is not 42:15 but a fair bit smaller. Given similar efficiency, the number of mA corresponds to the number of fotons produced, but a 405 nm foton carries more energy than a 650 nm one (about 60%).
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Old 12-18-2008, 02:24 PM #7
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Originally Posted by chimo
Keep in mind you have listed current to the LDs and not the power to them. *The forward voltage of the Bluray is probably around double that of the red LD. *That brings the power going into both a little closer. *The rest can likely be explained by the ability to focus the beams and the energy absorption rate for the different light wavelengths.
I do not have a Laser Power Meter - so current is the only relevant known variable that I've got to go on.
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Old 12-18-2008, 09:26 PM #8
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Originally Posted by Ironbar
[quote author=chimo link=1229480441/0#4 date=1229576777]Keep in mind you have listed current to the LDs and not the power to them. *The forward voltage of the Bluray is probably around double that of the red LD. *That brings the power going into both a little closer. *The rest can likely be explained by the ability to focus the beams and the energy absorption rate for the different light wavelengths.
I do not have a Laser Power Meter - so current is the only relevant known variable that I've got to go on. *
[/quote]

I was referring to the power going into the LDs. The power in = Voltage x Current. *Both are measurable with a multimeter. *Blurays have a much higher forward voltage than red LDs for a given current.

For example:
Let's say the forward voltage of the red LD is 2.5V at 420mA. *Power in = 1.05Watts
Let's say the forward voltage of the Bluray LD is 5.4V at 150mA. *Power in = 0.81Watts

In this example, the current ratio going to the diodes is 2.8:1, but the power ratio only 1.3:1 *

Another factor is each LD's efficiency at converting electrical energy to photons. *Optical power out is a fraction of the electrical power in. (IIRC it is roughly in the range of 1/4 to 1/2 - others feel free to chime in and add additional data). Manufacturers are continually striving to make more efficient LEDs.


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Old 12-18-2008, 11:48 PM #9
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Originally Posted by chimo
Another factor is each LD's efficiency at converting electrical energy to photons. *Optical power out is a fraction of the electrical power in. (IIRC it is roughly in the range of 1/4 to 1/2 - others feel free to chime in and add additional data).
Well, to complicate things, there are 2 efficiencies (or losses) at work:

First of all, not every passing electron releases a foton. Emission efficiency is in the order of 25-50% or so, which is one thing that can be optimized further.

The other is that you put more energy per electron in than is contained in the foton in releases. This efficiency varies a bit, but is generally worse for shorter wavelength. For example, a red diode might run at 2.8 volts, at 650 nm yielding 1.9 eV foton energy (67%). A blu ray might run at 5.5 volts, giving 405 nm or 3.1 eV per foton (56%).

Both factors contribute, and the total gives electrical to optical power, resulting in something around 25% for reds and 15% for blu rays. IR laser diodes are generally more efficient, up to 33% or even more.
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Old 12-19-2008, 12:08 AM #10
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Originally Posted by Benm
[quote author=chimo link=1229480441/0#7 date=1229639203]
Another factor is each LD's efficiency at converting electrical energy to photons. *Optical power out is a fraction of the electrical power in. (IIRC it is roughly in the range of 1/4 to 1/2 - others feel free to chime in and add additional data).
Well, to complicate things, there are 2 efficiencies (or losses) at work:

First of all, not every passing electron releases a foton. Emission efficiency is in the order of 25-50% or so, which is one thing that can be optimized further.

The other is that you put more energy per electron in than is contained in the foton in releases. This efficiency varies a bit, but is generally worse for shorter wavelength. For example, a red diode might run at 2.8 volts, at 650 nm yielding 1.9 eV foton energy (67%). A blu ray might run at 5.5 volts, giving 405 nm or 3.1 eV per foton (56%).

Both factors contribute, and the total gives electrical to optical power, resulting in something around 25% for reds and 15% for blu rays. IR laser diodes are generally more efficient, up to 33% or even more.
[/quote]

Do you think we have given the OP enough info to get totally confused yet? *

There's lots of great info here for people to digest. *Cheers,

Paul
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Old 12-19-2008, 04:21 PM #11
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Do you think we have given the OP enough info to get totally confused yet?
Probably... but he started it by mentioning phyisics and elaborate in the same post
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Old 12-20-2008, 10:25 PM #12
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

I'm a little confused too. I think I'll let scientists worry about making more efficient diodes for now
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Old 12-20-2008, 11:40 PM #13
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Surely.. knowing what the cause of inefficiency is doesn't make the solution trivial at all.

Great progress has been made especially with LEDs in the last couple of years. For lasers the actual efficiency matters less, unless the heat becomes a big problem.
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Old 12-30-2008, 08:10 PM #14
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Default Re: Burning: *PHR-803T blu-ray vs LG 20x red

Quote:
Originally Posted by chimo
[quote author=Ironbar link=1229480441/0#6 date=1229613863][quote author=chimo link=1229480441/0#4 date=1229576777]Keep in mind you have listed current to the LDs and not the power to them. *The forward voltage of the Bluray is probably around double that of the red LD. *That brings the power going into both a little closer. *The rest can likely be explained by the ability to focus the beams and the energy absorption rate for the different light wavelengths.
I do not have a Laser Power Meter - so current is the only relevant known variable that I've got to go on. *
[/quote]

I was referring to the power going into the LDs. The power in = Voltage x Current. *Both are measurable with a multimeter. *Blurays have a much higher forward voltage than red LDs for a given current.

For example:
Let's say the forward voltage of the red LD is 2.5V at 420mA. *Power in = 1.05Watts
Let's say the forward voltage of the Bluray LD is 5.4V at 150mA. *Power in = 0.81Watts

In this example, the current ratio going to the diodes is 2.8:1, but the power ratio only 1.3:1 *

Another factor is each LD's efficiency at converting electrical energy to photons. *Optical power out is a fraction of the electrical power in. (IIRC it is roughly in the range of 1/4 to 1/2 - others feel free to chime in and add additional data). Manufacturers are continually striving to make more efficient LEDs.


[/quote]

Oh, I understand completely Ohm's Law and how to calculate electrical power - I learned it when we were still using E for voltage. *

Since (P=IE) =| optical power, I figured that electrical power was kind of irrelevant. *
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