# Watts to Estimate Lumens or CD?

Discussion in 'General Electronics Chat' started by ChiketyBrikety, Feb 5, 2018.

1. ### ChiketyBrikety Thread Starter New Member

Feb 5, 2018
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If I know the watts and voltage of an incandescent light bulb, is there a general rule of thumb as to how bright the light bulb will be? Is there some chart equating watts to Lumens/CD?

Apr 5, 2008
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Jan 29, 2010
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4. ### DickCappels Moderator

Aug 21, 2008
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The correct unit is the Lumin which is something like the optical power as seen by a human eye and is irrespective of how the light is distributed. The Candela is related to apparent brightness and can be increased by narrowing the power in the beam to a smaller viewing angle.

This calculator might get you close to the ballpark but there are no guarantees.
https://www.rapidtables.com/calc/light/watt-to-lumen-calculator.html

5. ### Janis59 Active Member

Aug 21, 2017
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The very old and non-effective lamps like those in vehicle turn indicator has VERY roughly 1 W = 1 CD. However more modern "calorific bombs" has about twice or triple that, thus as an example, the average 100 W lamp gives out about 1500 Lm but 25 W gives 375 Lm what makes about 1...2 % it`s energetic to optic efficiency factor. Need to tick with a finger that average LED element of 3x4 mm large exerts at least a 350-650 Lm or even more, having some 0,3 W or 0,5 W. However this looks more like illusion, because the incandescent gives a semi-natural spectral distribution, or at last Gaussian tail, but a LED gives rather narrow spectral peak as those I measured few days about: at 380nm 0,1%, at 390 about 3% at 400 100% at 410 80% at 420- 30% at 430- 2%. How do You think Your eyesight neurons react on such garbage - some few % of them cries to brain - oh darling, stop it immediately, its so bright I cannot to stand. While another 90_ % claims to brain - Oh Master, give a more light, it is so damn dark we cannot see anything.
Brain of course don`t be trained to realize so contradicting information, so it answers with a headache, what never be happened if we use a oldy-goody incandescent "calorific bomb".
For comparison, the modern spiralized plasma lamps are much more eyesight-friendly, but less effective, and what is most drastic - they are quite much radioactive.
Only week ago we invited school-pupil from elite gymnasium to produce their pupil-science-job at our institute, thus I helped them to organize a "lead house" and to put in it the Geiger-Muller counter. We checked some four types of mini lamps of different view and different producers, and all them was about 4 to 6 natural background levels high. Because one of inert gases in them is isotope-rich. After we crushed the lamp, caring about to not spill those small Hg droplet, the radioactivity was gone - thus sure, the source was in the gas filling.

6. ### Audioguru Expert

Dec 20, 2007
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I had some "long life" incandescent bulbs that glowed orange instead of white. There looked dim but used the same amount of current as brighter light bulbs because less power made light and more power made heat..

Feb 5, 2018
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Thanks guys.