Post by Penny
On Thu, 26 Dec 2019 08:10:18 +0000, "J. P. Gilliver (John)"
Post by Penny Post by J. P. Gilliver (John)
those - and ultraviolet). (They never did make ones where the LED
actually emits white: "white LEDs" are actually blue/UV, but have
phosphor in them that absorbs blue/UV and glows white.)
And guaranteed to provoke a migraine in me, as I discovered recently when I
bought some new solar-powered motion-sensor outdoor lights and used one in
the hallway for a few days. I'm very glad I didn't go for the LED option
when replacing a fluorescent tube the other day.
Odd, since fluorescents use phosphors too (which fluoresce, hence the
name) - and for the same reason: the light source (semiconductor "chip"
in the LEDs, spark along the length of the tube for fluorescents) puts
out most of its light energy in the part of the spectrum we don't see,
and the phosphor makes it visible. I guess they are spectrally
different, though; white LEDs _mostly_ _do_ look bluer, I agree. I say
mostly, because "warmer" white LEDs are starting to appear: the little
desk lamp I have (Lidl, telescopic, _not_ magnifying) I'd swear had a
filament bulb if I didn't _know_ it was LEDs.
Post by Penny
I'm a bit confused by the thought the blue (and presumably the white)
require a higher voltage (though it was probably when failing to understand
electrickery that I hit my 'I can't do physics' wall). I bought a cheap
string of solar-powered blue lights. Although the battery box is designed
to hold 4 AA batteries it is only wired for 2 so the lights don't stay on
very long - they might stay on 'til bedtime in the summer. Had I chosen a
different colour would they be lit for longer?
You'll probably find that box does more than just _hold_ the cells; it
(or some other innocuous-looking part of the system) almost certainly
contains a little lump of electronics that converts the battery voltage
(over quite a range, too, probably) to what the LEDs require. If you
shake your head when viewing the lights in near-dark (so that the lights
make a streak of light on your retina/brain, like when you wave
sparklers around)), you'll probably see they're not on steadily, but
flashing very fast. If so, that'll confirm they're running from a
"switched-mode power supply" (SMPS) that changes the voltage. [Note that
the solar-powered cats' eyes that are appearing in a lot of our
motorways and 'A' roads are ditto; you can see the dotted trail as you
Post by Penny
Then there's the colour changing light-on-a-stick which cycles through
blue/red/green and only has one bulb...
That "bulb" will actually contain at least a red, green, and blue LED,
plus the electronics to fade them up and down in various combinations.
(The actual chips in LEDs are very small - a millimetre or two, except
for really powerful ones - meaning they can be placed so close together
you can't tell they're not one source, especially if there's any sort of
diffuser [milky housing].)
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf
Advertising is legalized lying. - H.G. Wells