Technical bulb advice

[nutty_nick]

Can anyone help me, I run a p21 12v bulb in the front of my bike (car indicator bulb adapted to fit my headlight) was wondering if anyone knew what the lumens was on one have had a google but its very contradicting and id like to convert it to an LED but without knowing the lumens I cant really complare the brightnesses, I want to improve the light not made it worse ! !

[Evil Hans]

Hard to be precise, but it's probably a few hundred lumens

For example, this one's 460:

https://www.svetila.com/en/car-bulbs-12v/494-p21w-12v-21w-7506-ba15s-original-line.html
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Triumph Sprint ST 1050. And it's Red.

[steve the grease]

[stinkwheel]

Whatever it is, a decent LED will be brighter than a filament (non-decent LEDs also available).

The tricky bit in terms of road legality is focus. How are you achieving a beam pattern?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

Yeah, watch out: some LED bulbs to a good job of replicating the direction nature of hi/lo beam bulbs where as others are just bright or super bright!

The flat or triangular ones do this better than round ones.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[WD Forte]

Most car indicator bulbs are 21W
the ball park figure on Lumens I got from tinterweb
is 14 lumens per watt for incandescent blubs
and 74 lumens per watt for leds
Roughly, 5 times light per watt

If the 14 vs 74 figures I read are to be relied on, a 21W blub gives 294 lumens
so a 4W led should give similar results.

A 21W led would give 1554 lumens, I have one outside on my security light and it's damn bright!
My 55/65W H4 bike headlamp probably gives around 770/990 Lumens in comparison

As well as focus issues, buyer beware as many of the Auto leds I've seen advertised the wattage figures are often
confused and equivalent bulb power used instead of actual led power, so bear that in mind especially on a small
bike with limited charging and battery power.

Then there's quality, led type and colour temperature.........
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bikers smell of wee

[WD Forte]

BTW
My bikes been all led for ages bar the headlamp but I'm definitely in the market for an H4 led hi/lo alternative with no, or minor, focus issues.
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bikers smell of wee

[Easy-X]

[nutty_nick]

hi guys thanks for all the great info, the bike is a 1971 bsa ariel 3 running one of them little plastic Cev headlights with the single filament 6v 15w bulbs in as standard, but because I converted it to 12v it gave me the option of upgrading the bulb, found a p21 was teh right diameter and single filament so ground the pins off and sodlered the collar off of the original bulb onto the base and have it a 6w increase, as to beam pattern, there was barely enough power for the light to even reach the road before and now it doesnt look too bad, I certainly dont get flashed by drivers coming the other way, id rahter keep the original headlight as trying to keep the bike looking stock even though its heavily modified underneath (its in the show and tell thread), as they are only cheap ive ordered a small selection off of ebay to play with. will report back on how I get on, including wall pattern test comparison to a stock bike

[stinkwheel]

Is your bike positive earth? If it is, you may need to wire the bulb holder backwards.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[nutty_nick]

hi stinkwheel, no bike is running standar dhonda cub electrics albeit massively stripped down, so standard 12v neg earth

[Triton Thrasher]

I think the Ariel 3 had direct lighting and no battery.

That means the light was AC powered.
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Rrrrrrrrrrrrrrrrrr

[Easy-X]

Shit! Good point... I got some cheapo LED bulbs for the turd scooter. Doubt they'll handle AC
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[WD Forte]

The Ariel 3 was an ill concieved idea that helped BSA on its way down the shitter
It was a slow, ill braked, ill lit, POS that flopped
Nowadays it has curiosity value and probably a laugh to ride for 10 minutes or so
round a car park.
I dont know what 'beam pattern' you expect but all you'll get from that cheap plastic shell
will be brighter output than the stock 6v bulbs watt for watt, but nothing like a high/low beam pattern
unless you change the headlamp shell for something suitable for road use.
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bikers smell of wee

[stinkwheel]

[stinkwheel]

[Easy-X]

[stinkwheel]

[Triton Thrasher]

Rectifying the alternator’s output will waste about 20% of the power.

I don’t know how much that matters in your case. Maybe try a few different wattage LEDs and see which ones it’s capable of powering.

It will have lost some magnetism in the last 47 or so years.
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Rrrrrrrrrrrrrrrrrr

[stinkwheel]

[Triton Thrasher]

[Easy-X]

Thinking about my scooter I may as well just wire off the ignition circuit as the lights are fully switched, i.e. not wired with permanent running lights: off/side/on + hi/lo beam.

Hmm... would it be better to run a relay to grab power from the battery directly or would standard wiring handle 2x 8W LED H4s + side lights? Probably less than 2 amps.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter