How do I calculate lumens?

[mdocod]

[email protected]=5.28W>84 lumen. ~16 lm/w

at 4.8V, this bulb is really being driven VERY gently. only delivering 16lm/w is an indication that it would have about 1000-2000 hours life at that drive level.

I'm pretty sure krypton bulb re-rate formulas are different than halogen/xenon. Seems I recall reading somewhere that krypton lamps have less extreme responses to changes in voltage. (the exponents are lower in the formulas).

but assuming the regular formulas.
@7.2V it would be @1.375A. 9.9W. Assuming the original lamp life was around 1500 hours, the new lamp life is around 10 hours.
Lumens re-rate to 344,. So torch lumens would be about 223. ~35 Bulb lumen/watt, which is about right for a lamp driven pretty hard..

it could be less than that... I think Mark is on to something with the new gas-fill lamps probably dissipating heat differently than vacuum lamps. Something closer to 3-3.3 probably is more appropriate for the lumen re-rating. Life rerating may be a little less harsh than ^12,


[edit] I'm not sure how you came up with 425 lumens, must have made an error

 

[dlrflyer]

I took 7.2v divided by 4.8v to come up with 1.5. Took 1.5 to the 3.5 power, comes out to a hair over 5. Took that number(5.0625) and multiplied by 84 lumens to get 425.25 lumens. Bulb life was rated at 15 hrs. My info came from Energizer and from Don's Bulbs website.(Both identical) This bulb came from my Energizer Hard Case 4D lantern that I'm wanting to hotwire as above, I just recycled the bulb into my 2D Mag. I think it's a neat bulb. Waste not want not

 

[mdocod]

1.5^3.5=4.133

 

[dlrflyer]

I don't have a scientific calculator so I used this website.

http://www.webwinder.com/wwhtmbin/jexpont.html

I tried a couple of easy ones like 2 to the 3rd power and it came out accurate.

 

[mdocod]

after playing with that one a minute, I noticed why it's not working right, it is not capable of handling exponents with decimals, it rounds to the next whole number... try again with 1.5^4 and you'll get the same result and realize what I am talking about.

I'm pretty sure mac, pc, most linux, just about every operating system distribution comes with a calculator app, you sometimes have to set a preference to change it to scientific calc.

 

[winny]

Peoples estimates of about 200 lumen at 12 V seems about right, but too high if any. If you look here: link, more than 20 lm/W is unrealistic at 8.4 W, assuming 100 hour bulb life. That is at 12 V.
From there, you can use the overdrive formula the same people are suggesting to calculate it at 14.4 V.