What's different of Bulb Lumens & Torch Lumens ?

[cenz]

I think many folks heard those terms...
as far as I know that Bulb Lumens is always more than Torch Lumens in the same bulb... and how to measure that ? Will the reflector affects the result of Torch lumens?

 

[adirondackdestroyer]

I think many folks heard those terms...
as far as I know that Bulb Lumens is always more than Torch Lumens in the same bulb... and how to measure that ? Will the reflector affects the result of Torch lumens?

Bulb lumens are what the light *should* put out at a given current.
For example some manufacturers claim what the LED should give at a given drive level, but in reality there are losses caused by the reflector and the fact that not all of the light is emitted forward.
I wish all manufacturers used Torch lumens because then there wouldn't be so much confusion. You can measure torch lumens with either an Intregrating Sphere which is VERY expensive, or by rigging up a light box to a lux meter. The second method isn't exact but it gives a pretty good idea.
Yes the reflector affects the result of the torch lumens.

 

[DM51]

The conversion is generally agreed to be bulb lm x 0.65 = torch lm. Search me why it isn't the far simpler 2/3! There is obviously some variation with different emitters, reflectors etc, but 2/3 gives you a good idea.

Most manufacturers quote output in bulb lumens, but a small minority use torch lm. Surefire uses an even more conservative formula which incorporates a reading over a complete discharge cycle, so their figures look lower than they appear.

 

[mdocod]

For LEDs the loss isn't as bad, 0.65 is the approximate conversion for loss of lumens when dealing with a bulb in a reflector. Keep in mind that a bulb emits in ALL directions so some light is lost because it escapes around the little hole that the bulb mounts up through.. LEDs emit light on a "half-sphere" so to speak... so little or no light is lost "out the back." so In an LED setup, The conversion to torch lumens is probably more like 0.8ish.

 

[LuxLuthor]

Previous posts have answered your question, but to make it really simple:

• Bulb Lumens ("BL") are specified by the manufacturer, and are the total lumens at a specified voltage of a bare bulb if you were to capture all the light by putting it inside of a measuring device called an "integrating sphere."

• Torch Lumens ("TL") are the total lumens coming out the front, beyond the (glass/plastic) lens...like if you pressed the light up against a flat screen and could measure all the lumens hitting the screen. This takes into account the shape, size, texture, and quality of the reflector, lens, and position of bulb in reflector for a given voltage. Based on a series of measurements and calculations, this rating is thought to be approximately 65% of the manufacturer's BL rating.

Many lights have a center "hot spot" which may change if light can be focussed, but neither of these terms specifically address the gradation of lumens from center hotspot to edge of beam.