6V MR11 versus 12V?

"Pete Biggs" <[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

I normally use the 12 volt versions of these bulbs but I'm thinking of
making an emergency backup 6V or 7.2V battery and carrying a 6V bulb. Of
course this would be half the weight & size of a 12 or 14.4V battery.

How do they compare in brightness when all else relevant is the same?

I'm wondering whether I'd need 5W or 10W to see where I'm going on unlit
roads at a decent speed. Only cheap 6V ones I can find so far are 18
degrees: less throw than 7 to 10 degree which I prefer.

Thanks.
~PB

I've got 6V MR11 lamps. One 5W and one 10W. The 5W is fine up to about 12
mph. Coming downhill at around 25 mph I use both together and they just
about do the job - on roads I know. I'm not sure about the throw angle but
18 degrees seems likely. My Petzal headtorch has a variable angle and I use
it as a spot, its 2W halogen (a conversion) gives me greater intensity but a
narrow field of view.

I'm looking to go to a 12V system sometime - so I can uprate to a 20W lamp.

So for backup use, 6V lamps are no problem.

John

Eatmorepies said:

I've got 6V MR11 lamps. One 5W and one 10W. The 5W is fine up to
about 12 mph. Coming downhill at around 25 mph I use both together
and they just about do the job - on roads I know. I'm not sure about
the throw angle but 18 degrees seems likely. My Petzal headtorch has
a variable angle and I use it as a spot, its 2W halogen (a
conversion) gives me greater intensity but a narrow field of view.

I'm looking to go to a 12V system sometime - so I can uprate to a 20W
lamp.

So for backup use, 6V lamps are no problem.

Thanks John. Is your battery (or dynamo) 6V? Perhaps a little more
wallop with 7.2V might make a 5W bright enough for 15 mph :-)

~PB

In article said:

Thanks John. Is your battery (or dynamo) 6V? Perhaps a little more
wallop with 7.2V might make a 5W bright enough for 15 mph :-)

Dynamos are closer to a current source than a voltage source. So it's
not so much a 6V dynamo, as a 0.5 amp dynamo which generates 6V if used
with a 3W bulb. So a 5W bulb would have to be designed to run at 10V to
work off a dynamo.

I am not sure if this is really relevant but FWIW...

....I use a CatEye ABS 6V system for commuting on a combination of lit
streets and unlit lanes. I have recently switched from a 10W Wide Bulb
to a 10W Spot Bulb as, when travelling at speed (20mph+) on the unlit
lanes, I could not reliably see far enough ahead. On the same system,
6V 5W would definitly not be enough for me for regular use.

On the other hand, as an emergency backup, it could be fine if you were
prepared to slow down.

"Pete Biggs" <[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

Eatmorepies said:

I've got 6V MR11 lamps. One 5W and one 10W. The 5W is fine up to
about 12 mph. Coming downhill at around 25 mph I use both together
and they just about do the job - on roads I know. I'm not sure about
the throw angle but 18 degrees seems likely. My Petzal headtorch has
a variable angle and I use it as a spot, its 2W halogen (a
conversion) gives me greater intensity but a narrow field of view.

I'm looking to go to a 12V system sometime - so I can uprate to a 20W
lamp.

So for backup use, 6V lamps are no problem.

Thanks John. Is your battery (or dynamo) 6V? Perhaps a little more
wallop with 7.2V might make a 5W bright enough for 15 mph :-)

Its a 7.2V NIMH. The load probably drops it to 6V when the lamp is on.

John

Eatmorepies said:

Its a 7.2V NIMH. The load probably drops it to 6V when the lamp is on.

No. The overvolting of the lamp is a standard trick for getting some
more light out. Apparently it actually works out as better value than
using a higher wattage lamp in terms of light output, although obviously
there is a reduction in lamp life.

Jon

Alan Braggins said:

Dynamos are closer to a current source than a voltage source. So it's
not so much a 6V dynamo, as a 0.5 amp dynamo which generates 6V if used
with a 3W bulb. So a 5W bulb would have to be designed to run at 10V to
work off a dynamo.

I'd spent a while recently trying to get my head around the current
source thing and you just successfully made sense of the whole thing in
two sentences.

Ta muchly

Jon

Jon Senior said:

Alan Braggins said:

Dynamos are closer to a current source than a voltage source. So it's
not so much a 6V dynamo, as a 0.5 amp dynamo which generates 6V if
used with a 3W bulb. So a 5W bulb would have to be designed to run
at 10V to work off a dynamo.

I'd spent a while recently trying to get my head around the current
source thing and you just successfully made sense of the whole thing
in two sentences.

I'd always thought of you as an electronic engineering genius, and it seems
you're just a mere mortal like us.

--
Ambrose

Pete Biggs said:

I normally use the 12 volt versions of these bulbs but I'm thinking of
making an emergency backup 6V or 7.2V battery and carrying a 6V bulb.
Of course this would be half the weight & size of a 12 or 14.4V
battery.

Would a battery of 10 AA cells to make 12V in a carrier be too much weight?
I'd say it may be easier to do that

Quoted message said:

How do they compare in brightness when all else relevant is the same?

Presumably pretty similar, given a similar amount of overvolting.

Quoted message said:

I'm wondering whether I'd need 5W or 10W to see where I'm going on
unlit roads at a decent speed. Only cheap 6V ones I can find so far
are 18 degrees: less throw than 7 to 10 degree which I prefer.

I've got a 6W (& 6V) bulb which I'm happy with to light my way on an unlit
road, but my decent speed is lower than your decent speed, and I seem to be
happier with a lot less light than many other people. At least for the next
10 years or so.
--
Ambrose

Ambrose Nankivell said:

Pete Biggs said:

I normally use the 12 volt versions of these bulbs but I'm thinking
of making an emergency backup 6V or 7.2V battery and carrying a 6V
bulb.
Of course this would be half the weight & size of a 12 or 14.4V
battery.

Would a battery of 10 AA cells to make 12V in a carrier be too much
weight? I'd say it may be easier to do that

I was considering that option but thought the backup battery might as well
be lighter still: 6 AA cells. Changing a bulb is a doddle with Lumicycle
lamps. I've already made a 12-AA battery -- alternative battery for short
rides, or bigger backup for long rides.

I wonder how 12V into 12V 5W would compare in brightness to 7.2V + 6V 10W?
There's a puzzle for the electrical mathematicians :-)

Quoted message said:

Quoted message said:

How do they compare in brightness when all else relevant is the same?

Presumably pretty similar, given a similar amount of overvolting.

I was assuming more volts equals greater brightness. Otherwise what's the
point of the weight of an extra 6 volt's worth of battery, besides a
greater choice of bulbs?

Quoted message said:

Quoted message said:

I'm wondering whether I'd need 5W or 10W to see where I'm going on
unlit roads at a decent speed. Only cheap 6V ones I can find so far
are 18 degrees: less throw than 7 to 10 degree which I prefer.

I've got a 6W (& 6V) bulb which I'm happy with to light my way on an
unlit road, but my decent speed is lower than your decent speed, and
I seem to be happier with a lot less light than many other people. At
least for the next 10 years or so.

Thanks Ambrose. I've now ordered both 5 and 10W 6V bulbs so I'll see what
they're like for myself. Will report on what speeds I can manage with
them... if I don't crash in the process ;-)

~PB

Pete Biggs said:

Ambrose Nankivell said:

Pete Biggs wrote:

<snip>

Quoted message said:

I wonder how 12V into 12V 5W would compare in brightness to 7.2V + 6V
10W?
There's a puzzle for the electrical mathematicians :-)

Quoted message said:

Quoted message said:

How do they compare in brightness when all else relevant is the same?

Presumably pretty similar, given a similar amount of overvolting.

I was assuming more volts equals greater brightness. Otherwise what's
the
point of the weight of an extra 6 volt's worth of battery, besides a
greater choice of bulbs?

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.
Watt is a measure of power, Volt is a measure of potential, Ampere is a
measure of current.
W = V * A
In other words: to run a 5W 6V bulb you need twice the amperes that you
need to run a 5W 12V bulb:
so a 6V 10 Ah battery may be half the size of a 12V 10Ah but it will run
your light for half the time too.
The general rule that nobody gives you anything for free still applies.

Fra

<snip>

Zap said:

Quoted message said:

I was assuming more volts equals greater brightness. Otherwise
what's the
point of the weight of an extra 6 volt's worth of battery, besides a
greater choice of bulbs?

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.
Watt is a measure of power, Volt is a measure of potential, Ampere is
a measure of current.
W = V * A
In other words: to run a 5W 6V bulb you need twice the amperes that
you need to run a 5W 12V bulb:
so a 6V 10 Ah battery may be half the size of a 12V 10Ah but it will
run your light for half the time too.
The general rule that nobody gives you anything for free still
applies.

Thanks very much! I should have known or worked out that very basic fact.

I'll take it as a mixture of bad and good news: evening out to "okay"
news! :-) The battery will deliver half the run time I was expecting, but
a 5W lamp should be bright enough for my emergencies, rather than a 10W.

~PB

Zap said:

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W
6V lamp to 7.2V will produce an increase in brightness.

Jon

"Jon Senior" <jon_AT_restlesslemon_DOT_co_DOT_uk> wrote in message
news:[email hidden]...

Quoted message said:

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W 6V
lamp to 7.2V will produce an increase in brightness.

Jon

Alledgedly for an incandescent bulb:

Light output is proportional to voltage to the power of 3.5
Efficiency is proportional to voltage to the power of 2
BUT
Bulb life is proportional to voltage to the power of -12

John

Jon Senior said:

Zap said:

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W
6V lamp to 7.2V will produce an increase in brightness.

That's right, but I'd be over-volting in the case of a 12V bulb too: 14.4
volts.

~PB

On Thu, 10 Nov 2005 21:35:45 -0000, Jon Senior

jon_AT_restlesslemon_DOT_co_DOT_uk said:

Zap said:

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W
6V lamp to 7.2V will produce an increase in brightness.

Of course you are right, what I meant is that a bulb rated 6V5W gives the
same light, when run at 6V, as a 12V5W bulb ran at 12V or a 240V5W ran at
240V etc.

Quoted message said:

Jon

"Zap" <zot> wrote in message news:[email hidden]...

Quoted message said:

On Thu, 10 Nov 2005 21:35:45 -0000, Jon Senior

jon_AT_restlesslemon_DOT_co_DOT_uk said:

Zap said:

Hi, first post here so I thought I'd say something useful:
I think that a 5W bulb gives the same light watever the voltage.

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W
6V lamp to 7.2V will produce an increase in brightness.

Of course you are right, what I meant is that a bulb rated 6V5W gives the
same light, when run at 6V, as a 12V5W bulb ran at 12V or a 240V5W ran at
240V etc.

Is that actually the case? I thought there was some efficiency gain from the
higher voltage - lower current, therefore thinner filament, which gives
higher efficiency.

cheers,
clive

Clive George said:

"Zap" <zot> wrote in message
news:[email hidden]...

Quoted message said:

On Thu, 10 Nov 2005 21:35:45 -0000, Jon Senior

jon_AT_restlesslemon_DOT_co_DOT_uk said:

Zap wrote:
> Hi, first post here so I thought I'd say something useful:
> I think that a 5W bulb gives the same light watever the voltage.

Excepting that if you increase the voltage into a incandescent lamp it
will burn increasingly brightly (Until it burns out). Overvolting a 5W
6V lamp to 7.2V will produce an increase in brightness.

Of course you are right, what I meant is that a bulb rated 6V5W gives
the
same light, when run at 6V, as a 12V5W bulb ran at 12V or a 240V5W ran
at
240V etc.

Is that actually the case? I thought there was some efficiency gain from
the
higher voltage - lower current, therefore thinner filament, which gives
higher efficiency.

huh you got me there, I don't know. I am inclined to presume that the
difference can not be too big thou.

I found this page that should give enough information on bicycle lights
issues:
<URL:http://user.fundy.net/cyclist/bikecurrent-FAQ.html>
maybe it can be of help if anybody wants to know more 🙂

Fra

Quoted message said:

cheers,
clive

Update:

I've now tried a 5W 6V MR11 with 6 AA cells. It's too good just for an
emergency back up. It makes a handy be-seen-by fog lamp! The
over-volting effect seems stronger than using 14 to 15V with the 12V
version of the same bulb -- you wouldn't believe it's just a 5W bulb to
look at. Run time: 2 hours with NiMH "2800" mAh.

Also rigged up a 7.2V AAA pack. I was expecting this to be useless but it
provides 50 minutes! (with the 5W bulb and 1000 mAh cells).

~PB