wow........thanks for all the high tech imput!!.......Robb

----- Original Message -----
From: "Peter Rebaudo" <reba...@pacbell.net>
To: "Silver list" <silver-list@eskimo.com>
Sent: Wednesday, September 17, 2003 9:54 AM
Subject: CS>LEDs


> Hi:
> For LEDs of kinds :
> <www.gilway.com>
> <www.eLumexLEDs.com>
>
> Title: About LED's,Candelas and Watts.
>
> Although this is not strictly a CS subject I think it's a useful
> adjuvant to it
> If I am wrong please accept my apologies.
>
> I shall make some statements, they are at the best of my knowledge,
> today. Of course comments and corrections are most welcome.
>
> Visible LED's are usually specified in Candela units. This units are
> weighted to the human eye response.
> When LED's are used for tissue irradiation the important Item is the
> forward (Light going forward, not in all directions) radiant power,
> expressed in Watts (or milliwatts) and since Watts x seconds = to
> Joules, the dose should be expressed in Joules (watts-second).
>
> To obtain the radiant power from LED manufacturers has proven rather
> difficult. So here are some numbers: (Values are approximations)
>
> MGMicro LED clusters (from used traffic signals)
> Red probably 660nm,
> At 1.8 volts, 20 mA, 600 mCd, 0.65 mW
> 2.0 45 1000 1.37
> Approximates Gilway E168
>
> Green probably 565 nm
> At 2.2 Volts , 20mA, 300 mCd, 0.064 mW
> 2.5 45 600 0.17
> Approximates Gilway E166
>
> As can be seen from the above numbers although the red and the green
> have the same "brightness" (600 mCd) the power emitted by the red is 10
> times that of the green.
> This relationship approx. holds for all reds Vs green LED's.
> Therefore the use of the candela measure can be misleading.
>
> Also LED's with wider view angles (2 Omega1/2) and the same Candela have
> more power output than narrower ones.
>
> Infrared LED's are usually specified in milliwatts per steradian .
> A steradian is a solid angle (3D's) which having its vertex at the
> center of the sphere, cuts off a spherical surface area equal to the
> square of the sphere radius.
> So in a 1 meter radius sphere an angle of 1 steradian will encircle an
> area of one square meter.
> Here care must be exercised, when the specs said an LED has a 20 mW/sr.
> It does not mean that if the power is measured in its center steradian
> angle it will be 20 mW's, The power density will be equal to 20 mW/sr
> only in the center one hundred of a steradian.
>
> So once again the thing that counts is: The total radiant power emitted
> forward.
>
> Example: Giway IR LED # E24 specified at 20 mw/sr (typical) has the
> following total power:
>
> At 1.4 Volts, 20 mA, 3.20 mW at zero distance from LED face.
> 2.54 mW at 1.0 cm (into a 1cm detector)
> 1.21 mW at 2.5 cm (into a 1cm detector)
>
> However if the power in the center 0.01 sr is measured and then is
> multiplied by 100 it will equal to 20mW/sr.
>
> In my experience irradiation with IR(880) and Red (660nm) clusters seems
> to help in a number of maladies.
>
> To build a powerful IR (72 LED's) cluster a kit can be purchased from
> the maker <www.dalewheat.com> or from BGMicro. <www.bgmicro.com>
> Complete kit $25.95 part # LED1069, Assembled and tested $35.95 LED 1070 .
> A weather resistant enclosed version for $59.95.
>
> The PCB part # LED1070, $9.95 can be used to built a RED version using
> Gilway #E184 LED's (660nm, 2000 mCd, min., 3500 mCd max.) Its power
> output at the led face is:
> At 1.85 V, 20 mA, 2.0 mW
> 2.00 V, 36 mA 3.5 mW
> 2.30 V, 60 mA 5.3 mW
> For continuous wave Operation, 200 Ohms resistors can be used.
>
> For pulsed operation the circuit provide by Walter Cook at
> <www.seanet.com/~waltc/page43.htm> is very useful.
>
> For extensive information on LED's and Laser Diodes, use and dosages see :
> Therapeutic Lasers Theory and Practice, by G.David Baxter,.
> Churchill Livingstone, Publisher.
>
> Last Comment:, Remember that:
>
> Power Density = Irradiance = Total Incident Power / Area. [Watts / cm^2]
> Radiant Exposure = Energy Density = Total Incident Energy / Area.
> [Joules / cm^2] = [Watts-sec/cm^2]
> Radiant Exposure Also is equal to:
> Total Power Density x Total Time of Irradiation [Watts/cm^2 x Seconds]
> Walter's schematic produces a frequency of 7 Hz at 50% duty cycle.
> Baxter states that a 4Hz frequency decreases sensitivity to pain
> immediately, Walter's circuit can be easily altered by changing a couple
> of components .
>
> Sincerely
>
> Peter R
>
>
>
>
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