Have you any evidence for that statement? IIRC, red was a danger colour long before the railways. Even although it is the most difficult colour to see. And so many males are red/green colour blind in low light conditions.
Logically, a danger signal should be the most visible to all?
My Sony clock radio has an LCD, the backlight isn't that bright, not at all noticeable in the dark, but good enough to see the numbers by. Though actually I normally look at my watch
On Wednesday 13 November 2013 21:45 WeeBob wrote in uk.d-i-y:
That was my favourite - I made one of those ^^^
Pale green/blue VFD. Very rare now.
Not so bad with an AMOLED display (no backlight). I use a smartphone as an alarm clock using an opensource app "AlarmKlock" that is no longer developed but I hack on the source a little to alter some parameters and give it a couple of features.
Best features:
Loads of alarms can be set one shot or to repeat on given days.
Nice and loud, but a gentle ramp up.
Big snooze "button" - can hit the face and get it without looking. The Alarm Off is a slider so hard to accidently activate.
It will sound for upto an hour. I have a Nuclear Siren as my sound :)
Me too...
I would certainly have the multiple alarms feature with day of week setting possible. MSF/DCF modules are available so that bit is easy.
That is actually a myth. The dark adapted eye is most sensitive to mid green and focusses best with green light. The optimum in total darkness is dim green light or even white light. You would be surprised how dim a light you can see by when dark adapted 10uA through a modern LED is enough to make a torch glow enough you can always find it in the dark. Battery life is not affected by this tiny leakage current.
Red light doesn't bleach the rhodopsin in rods much in a dark adapted eye which is why it was used in submarines but they have long since discovered that people have trouble reading fine charts and maps with only red light illumination so dim white or green is now preferred.
The pupil being wide open and the wavelength being at one extreme end makes the image blurry. It has become worse now that red LEDs are truly monochromatic. The old "red" filters let some yellow light through.
Some back lights are tastefully dim in the dark. I have a glow in the dark torch that is actually brighter than it for at least an hour.
It strikes me that the plastic used for that (not your usual feeble stuff but a dayglo yellow that glows bright green for hours) would be ideal in an emergency situation with no power like the Phillipines now.
what's wrong with audio signals, talkign clocks have been around for a while, you don'
You want a clock talking to you all night?
Only a memory of reading "Red For Danger" by LTC Rolt.
As for colour blindness, all railway staff are tested for it before they're allowed near the track.
It should also be totally unambiguous, and as I said, if you can see a red light, you know what colour it is, assuming you're not colour blind. With other colours, it's possible to see the light and not know what colour it is..
Many people can't focus red light to see detail with a dark adapted eye. Dim green or white light works much better for reading maps.
Not quite. Red is the longest wavelength we can see and as such suffers least scattering losses in the atmosphere. You cam see a red light from further away in conditions of poor visibility and that was a real advantage for train signalling in mist of fog. Yellow for caution isn't all that far behind in terms of penetrating power.
Short wavelength blue light is pretty hopeless by comprarison which is why the clear sky is visibly blue from scattered sunlight.
Red LEDs came first followed by yellow and then a feeble lime green.
There was an incredibly expensive early SiC blue LED used almost exclusively in high end audiophool snake oil products.
So you see a signal - but don't know what colour it is, so is safe to go?
That sounds apex over posterior to me.
As has been said, red may cut through fog rather better than other colours. But I reckon the idea of red for danger goes back way before any scientific experiments.
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