In article ,
Theo Markettos wrote:
I recently designed a PCB with a series of indicator LEDs for different
power rails, and decided to use a rainbow colour scheme
white/blue/green/yellow/orange/red
All but the white came from the same Kingbright range.

Not only were they painfully bright, they were all different levels of
intensity. I had to spend half a day tweaking the resistor values to
match the intensity across the array. To make it more exciting, the
power rails were different voltages. Some of the resistor values went
up by a factor of 100.

Nothing new there - even when there were only red green and amber ones
they'd look different when driven the same. It may even depend on the
individual's eyes.

--
*Procrastinate now

Dave Plowman London SW
To e-mail, change noise into sound.

On 05/07/2014 21:05, Bob Eager wrote:
A bit strange, this but perhaps someone has an idea or two.

I've just installed a rackmount KVM at home. Very nice, far better than
the old Belkin one.

It has a green power indicator LED on the front panel which is FAR too
bright! The rack almost faces my desk, and it's dazzling.

I could just stick insulation tape over it but I'd rather just dim it
down a bit. I don't want to open the thing up, so any ideas? Semi opaque
tape perhaps (suggestions?)

The problem on my Openreach modem is that the lights are surrounded by
ventilation slots. The Plusnet router is better. Need to design a
suitably ventilated box when I move them to their final location,
perhaps with a chimney to encourage flow.

whisky-dave wrote:
One problem is that our eyes have a differnt sensitivity to that of those
devices that measure brightness. They can also have diffenrt angles of
view which can be another annoyance.

I wonder how much that sensitivity varies too: hearing loss causes the
higher frequencies to go before the lower ones. I don't know how the
optical response curve varies between individuals.

You shouldn't use the voltage or current to change LEDs brightness you
shoud use constant cuttent and PWM to adjust the intensity.

Yes when the primary purpose is lighting. When the primary purpose is 'did
I forget to plug it in' or 'has my fuse blown', a PWM circuit is a little
OTT.

Theo

On Wed, 09 Jul 2014 11:23:10 +0100, Theo Markettos wrote:

whisky-dave wrote:
One problem is that our eyes have a differnt sensitivity to that of
those devices that measure brightness. They can also have diffenrt
angles of view which can be another annoyance.

I wonder how much that sensitivity varies too: hearing loss causes the
higher frequencies to go before the lower ones. I don't know how the
optical response curve varies between individuals.

I have a slight cataract in the eye, which makes it a bit worse I think.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £30a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

In article ,
Theo Markettos wrote:
I wonder how much that sensitivity varies too: hearing loss causes the
higher frequencies to go before the lower ones. I don't know how the
optical response curve varies between individuals.

Vastly.

If you create a lightbox which allows you to make any colour by mixing
RBG, and set it to the closest match to say a printed colour. Then get
someone else to do the same. The chances are they'll have different
settings.

Then try it with a narrow spectrum light like low pressure sodium or some
LEDs. The difference between two individuals will be even more marked.

Basically, we all 'see' colours differently. But learn to call them by the
same names.

--
*Strip mining prevents forest fires.

Dave Plowman London SW
To e-mail, change noise into sound.

On Wednesday, 9 July 2014 11:23:10 UTC+1, Theo Markettos wrote:
whisky-dave wrote:

One problem is that our eyes have a differnt sensitivity to that of those
devices that measure brightness. They can also have diffenrt angles of
view which can be another annoyance.



I wonder how much that sensitivity varies too:

Quite a bit also ambient light levels are important.
Your life style can also affect sensitivity.
Being partiallly or fully colour blind is another problem.


hearing loss causes the
higher frequencies to go before the lower ones. I don't know how the
optical response curve varies between individuals.

It's just not optical either show the same colour to two people and there;s a chance thy'll see a diffenc in shade.
Women can disiquish more colours than men apparently or rather a finer detail detwwen shades, that;'s why they moan about the curtains and scatter cushions not matching and therefor new ones are needed ;-).

There's a number of colour test charts that can be used to check monitors but the best don't rely on a human eye, there's got to be a reason for that.


You shouldn't use the voltage or current to change LEDs brightness you

shoud use constant cuttent and PWM to adjust the intensity.



Yes when the primary purpose is lighting. When the primary purpose is 'did
I forget to plug it in' or 'has my fuse blown', a PWM circuit is a little
OTT.

It's the best and standard way to dim LEDs other than sticking something over them.
I set the LEDs on my virgin superhub 2 to low, doing that the conventional way would require a switch to be set to low meduim or high rather than software.

It's not really OTT because leds aren't all the same even the same colours because of manufacturing differencies the voltage they 'run' at can be slightly differrent which means a slightly differnt current will flow LEDs are very suceptable to heat and that changes their characteristics too.

and using resistors you have very little riggle room unless you spend a lot on high tolerance resistors.

On 09/07/2014 11:23, Theo Markettos wrote:
I wonder how much that sensitivity varies too: hearing loss causes the
higher frequencies to go before the lower ones.

Not always - I have lost a chunk in the middle.

--
Rod

On 09/07/2014 11:58, whisky-dave wrote:
It's just not optical either show the same colour to two people and there;s a chance thy'll see a diffenc in shade.
Women can disiquish more colours than men apparently or rather a finer detail detwwen shades, that;'s why they moan about the curtains and scatter cushions not matching and therefor new ones are needed;-).

There is a degree of irony that colour blind people are sometimes far
more sensitive to colour mis-matches than those with "normal" colour
vision. Classic being where they don't even have to do more than glance
where others need to spend ages carefully scrutinising - and may still
end up not seeing a difference.

--
Rod