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How Bright is Bright?
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Tim Wescott
Nov 15, 2012, 5:17:03 PM11/15/12
to
I'm not calibrated here.
I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
DigiKey had. At 4mcd per, they're just barely bright enough on the bench
but not when I put the board into a case and look through windows at the
LEDs.
I have used 0603 LEDs that are so bright at rated current it hurts to
look at them, but (@#$%) I can't find the part numbers.
I'm wondering what sort of brightness I should be aiming for in the
replacement devices -- if 4mcd is barely visible in a bright room, is
20mcd going to be enough, or should I be looking at 100mcd, or what?
(I guess that boils down to: are my eyeballs logarithmic the same as my
ears, or are they roughly linear?).
I'm assuming that I have some room for adjustment by changing the current
into the things, but I also assume that running one way dimmer than rated
is going to make strange things happen. So I'd kind of like to come
close with whatever I get.
TIA.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
DigiKey had. At 4mcd per, they're just barely bright enough on the bench
but not when I put the board into a case and look through windows at the
LEDs.
I have used 0603 LEDs that are so bright at rated current it hurts to
look at them, but (@#$%) I can't find the part numbers.
I'm wondering what sort of brightness I should be aiming for in the
replacement devices -- if 4mcd is barely visible in a bright room, is
20mcd going to be enough, or should I be looking at 100mcd, or what?
(I guess that boils down to: are my eyeballs logarithmic the same as my
ears, or are they roughly linear?).
I'm assuming that I have some room for adjustment by changing the current
into the things, but I also assume that running one way dimmer than rated
is going to make strange things happen. So I'd kind of like to come
close with whatever I get.
TIA.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
alie...@gmail.com
Nov 15, 2012, 5:46:19 PM11/15/12
to
On Nov 15, 2:17 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
I know this one!
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
http://en.wikipedia.org/wiki/Stevens%27_power_law
See table at right.
> I'm assuming that I have some room for adjustment by changing the current
> into the things, but I also assume that running one way dimmer than rated
> is going to make strange things happen. So I'd kind of like to come
> close with whatever I get.
>
> TIA.
Mark L. Fergerson
Simon Stroud
Nov 15, 2012, 6:14:55 PM11/15/12
to
"nu...@bid.nes" <alie...@gmail.com> wrote in message
news:3a4d5b68-1699-402b...@jj5g2000pbc.googlegroups.com...
On Nov 15, 2:17 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
> I'm assuming that I have some room for adjustment by changing the current
> into the things, but I also assume that running one way dimmer than rated
> is going to make strange things happen. So I'd kind of like to come
> close with whatever I get.
>
> TIA.
I know this one!
http://en.wikipedia.org/wiki/Stevens%27_power_law
See table at right.
You're welcome.
Mark L. Fergerson
This page has some pictures of experiments involving varying the LED current
> into the things, but I also assume that running one way dimmer than rated
> is going to make strange things happen. So I'd kind of like to come
> close with whatever I get.
>
> TIA.
I know this one!
http://en.wikipedia.org/wiki/Stevens%27_power_law
See table at right.
You're welcome.
Mark L. Fergerson
and getting different perceived brightness:
http://led.linear1.org/how-is-led-brightness-related-to-current/
The relationship between LED current and perceived brightness is VERY
non-linear. I recently had to implement a PWM LED brightness controller in
an FPGA. For my application I only needed 16 brightness steps, but my FPGA
needs a timing resolution of at least 256 steps. The first non-zero
brightness level (i.e. step 1 in the range 0-15) only needs the LED to be on
with a duty cycle of 1 in 256. The last step before fully-on (i.e.
brightness 14 in the range 0-15) has a duty cycle of 217 in 256. Values in
between are suitably spaced in a non-linear way using a look-up-table. This
gives 16 brightness steps that "appear" pretty equal.
In another recent bit of design work, I needed to pass a tiny current
through an LED even when "off" to allow detection of LED failure. Even at
the lowest current that I could detect with my monitoring circuit (just over
1uA) there was still a visible glow that was deemed to be too much. The
final solution was to only apply this tiny test current occasionally for a
very short pulse.
Regards,
Simon.
mike
Nov 15, 2012, 8:58:17 PM11/15/12
to
On 11/15/2012 2:17 PM, Tim Wescott wrote:
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
>
> I'm assuming that I have some room for adjustment by changing the current
> into the things, but I also assume that running one way dimmer than rated
> is going to make strange things happen. So I'd kind of like to come
> close with whatever I get.
>
> TIA.
>
Your eyes have a limited dynamic range accompanied by a slower acting
> I'm not calibrated here.
>
> I have a board onto which I unthinkingly put the cheapest 0603 LEDs that
> DigiKey had. At 4mcd per, they're just barely bright enough on the bench
> but not when I put the board into a case and look through windows at the
> LEDs.
>
> I have used 0603 LEDs that are so bright at rated current it hurts to
> look at them, but (@#$%) I can't find the part numbers.
>
> I'm wondering what sort of brightness I should be aiming for in the
> replacement devices -- if 4mcd is barely visible in a bright room, is
> 20mcd going to be enough, or should I be looking at 100mcd, or what?
>
> (I guess that boils down to: are my eyeballs logarithmic the same as my
> ears, or are they roughly linear?).
>
> I'm assuming that I have some room for adjustment by changing the current
> into the things, but I also assume that running one way dimmer than rated
> is going to make strange things happen. So I'd kind of like to come
> close with whatever I get.
>
> TIA.
>
offset (probably some changes in dynamic range too)...aka dark adaptation.
The apparent brightness of the led will vary with the recent history
of your eyes. A led in a dark room doesn't have to be nearly as bright
as one in daylight.
The purpose of the light also matters. If it's intended to be an alarm
condition that requires attention, you might want it brighter than a
status led.
I don't think there's any substitute for "taking a look at it"
in the actual operating environment.
LED light output vs current is yet another issue.
Vladimir Vassilevsky
Nov 16, 2012, 10:01:35 AM11/16/12
to
"Simon Stroud" <simon....@btoutternet.com> wrote in message
news:vIadnUB3ItTy6jjN...@supernews.com...
>
> The relationship between LED current and perceived brightness is VERY
> non-linear.
A square law works very well. Could be implemented with trivial circuilt.
> The relationship between LED current and perceived brightness is VERY
> non-linear.
> I recently had to implement a PWM LED brightness controller in an FPGA.
> For my application I only needed 16 brightness steps, but my FPGA needs a
> timing resolution of at least 256 steps. The first non-zero brightness
> level (i.e. step 1 in the range 0-15) only needs the LED to be on with a
> duty cycle of 1 in 256. The last step before fully-on (i.e. brightness 14
> in the range 0-15) has a duty cycle of 217 in 256. Values in between are
> suitably spaced in a non-linear way using a look-up-table. This gives 16
> brightness steps that "appear" pretty equal.
> In another recent bit of design work, I needed to pass a tiny current
> through an LED even when "off" to allow detection of LED failure. Even at
> the lowest current that I could detect with my monitoring circuit (just
> over 1uA) there was still a visible glow that was deemed to be too much.
> The final solution was to only apply this tiny test current occasionally
> for a very short pulse.
VLV
Cydrome Leader
Nov 16, 2012, 2:05:47 PM11/16/12
to
the LEDs are always sort of flashing, but not really as the panel idles in
a self test mode.
Tim Williams
Nov 16, 2012, 6:44:33 PM11/16/12
to
"Vladimir Vassilevsky" <nos...@nowhere.com> wrote in message
news:GKKdnT9P56jJyDvN...@giganews.com...
that I put in animations and a tone generator!
http://www.youtube.com/watch?v=_L6BNZXwMxg
(This one displaying just the intensity modulation, but the "8's" can be
scrolling text; meanwhile, a one-shot digital timer was used to generate
chiptunes.)
The exact profile used in that animation was,
wave .byte 4, 14, 28, 64, 255, 64, 28, 14 ; waviness
.byte 4, 14, 28, 64, 255, 64, 28, 14
wave2 .byte 3, 3, 10, 40, 144, 144, 40, 10 ; halfway interpolation
.byte 3, 3, 10, 40, 144, 144, 40, 10
So the full sequence was 3, 4, 10, 14, 28, 40, 64, 144, 255, and back
down, which as I recall, I approximated from an A*exp(sin(t) + 1) type
function. Obviously, the pulse width here is 0-255 out of 255, as in
Simon's case.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
news:GKKdnT9P56jJyDvN...@giganews.com...
>> I recently had to implement a PWM LED brightness controller in an FPGA.
>> For my application I only needed 16 brightness steps, but my FPGA needs
>> a
>> timing resolution of at least 256 steps. The first non-zero brightness
>> level (i.e. step 1 in the range 0-15) only needs the LED to be on with
>> a duty cycle of 1 in 256. The last step before fully-on (i.e.
>> brightness 14
>> in the range 0-15) has a duty cycle of 217 in 256. Values in between
>> are suitably spaced in a non-linear way using a look-up-table. This
>> gives 16 brightness steps that "appear" pretty equal.
>
> Wow. FPGA for LED control. Incredible.
I know, right? I did that on a frickin' Z80, with enough cycles to spare
>> For my application I only needed 16 brightness steps, but my FPGA needs
>> a
>> timing resolution of at least 256 steps. The first non-zero brightness
>> level (i.e. step 1 in the range 0-15) only needs the LED to be on with
>> a duty cycle of 1 in 256. The last step before fully-on (i.e.
>> brightness 14
>> in the range 0-15) has a duty cycle of 217 in 256. Values in between
>> are suitably spaced in a non-linear way using a look-up-table. This
>> gives 16 brightness steps that "appear" pretty equal.
>
> Wow. FPGA for LED control. Incredible.
that I put in animations and a tone generator!
http://www.youtube.com/watch?v=_L6BNZXwMxg
(This one displaying just the intensity modulation, but the "8's" can be
scrolling text; meanwhile, a one-shot digital timer was used to generate
chiptunes.)
The exact profile used in that animation was,
wave .byte 4, 14, 28, 64, 255, 64, 28, 14 ; waviness
.byte 4, 14, 28, 64, 255, 64, 28, 14
wave2 .byte 3, 3, 10, 40, 144, 144, 40, 10 ; halfway interpolation
.byte 3, 3, 10, 40, 144, 144, 40, 10
So the full sequence was 3, 4, 10, 14, 28, 40, 64, 144, 255, and back
down, which as I recall, I approximated from an A*exp(sin(t) + 1) type
function. Obviously, the pulse width here is 0-255 out of 255, as in
Simon's case.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
Paul Hovnanian P.E.
Nov 19, 2012, 9:12:53 PM11/19/12
to
Display brightness is usually specified in NITs (cd/m^2). So it depends on
the area that is emitting the light. Some useful information:
http://en.wikipedia.org/wiki/Candela_per_square_metre
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Dyslexics have more fnu.
the area that is emitting the light. Some useful information:
http://en.wikipedia.org/wiki/Candela_per_square_metre
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Dyslexics have more fnu.
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