nuckolls.bob(at)aeroelect
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 Posted: Mon Aug 24, 2020 10:17 am Post subject: Fwd: MR16 halogen lamp LED replacement: sanity check |
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At 10:38 AM 8/24/2020, you wrote:
| Quote: | While looking for a 'drop in' LED replacement for some 75W MR16 (2" dia) landing light lamps, I've found 'more of the same' in actual LED lumens ratings vs the lumens ratings for the incandescent or halogen bulbs they are replacing. 75W halogens are typically around 2500 total candela (sp?) and 1400 lumens, while the claimed replacements are closer to 500-600 lumens. When I asked one of the common vendors about that, well, see the answer below.Â
It seems it's time to question someone's sanity. Who's?
Charlie |
Illumination for night landings is
a topic that will get you a constellation
of opinions . . . but not much in the
way of practical experience combined
with good physical definitions.
Those Lumens numbers are pretty much
meaningless without knowing exactly how
they e distributed. Lenses and
reflectors have an understandably profound
effect on where the light goes. There are
hand held flashlights with 2W leds that
produce a 6000 Lumen BEAM . . . the
multi-led headlight arrays on my truck's
headlights consume about 30 watts but
wont have anywhere near that kind of
output center-beam . . . but probably
something on that order of light output
SPREAD OUT over a large area of illumination.
I recall reading the FAA requirements for
landing and taxi light functionality
while working at GatesLJ on the GP180
project.
It called for verifying, by measurement,
incident illumination over the illuminated
surfaces with defined H, V, and D values.
NOT something we wanted to do in house . . .
we bought Grimes fixtures already qualified
to those requirements.
Needless to say, those were flame-throwing
fixtures!
On the other side of the coin, I recall
a 'demonstration' I used to conduct at
my seminars. I'd light up a 6 volt sports
lantern and shine it around my audience
with pretty much everyone ducking for
cover.
Question: "Could you land an airplane at
night by simply holding this light out the
window?" 6 volts at 0.75A = 4.5 watt
bulb. Obviously intense beam power but a
good deal of peripheral emission as well.
The answer was: "You betcha . . . no sweat."
When considering a shift of technology in
your lighting selections, the BEST thing
to do is go fly it yourself. I can tell
you from personal experience that ANY
light thrown out the front when on short
final to a black hole is of HUGE benefit.
The human eye is a logarithmic sensor. A
2x increase in illumination will be noticed
but not perceived as a 'big' change. A
10:1 reduction in illumination will be
startling . . . but will probably not
make your task of greasing the landing
more difficult.
I made an interesting discovery during
night ops instruction at KICT. The
instructor directed me to the much wider
runways to figure out how to land with
NO lights. The 4x wider runway really
changed your perception of height looking out
the windshield!
After the first few clumsy arrivals with
the concrete, I discovered that the strobe
flashes illuminated the surface under the
wing tips. I noticed that the first flash I
could perceive texture in the peripheral
view of the pavement, I was but a couple
feet off the ground.
The point is that you don't really need
to see possums creeping across the runway
2000' ahead. Getting a good situational
awareness of immediate environs will get
you on the ground quite comfortably . . .
and it doesn't take much light to do that.
But everyone's goals, skill-sets and
perceptions are different. When in doubt,
go fly it. Last time I looked, we're still
allowed to do that.
I'd bet that your proposed substitution
for a lamp will be perceived as 'different'.
Question: "Is it adequate?"
Bob . . .
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