What's the Truth about Lumens vs Watt Equivalency in LED Downlights?

[MattinCA]

Google tells me a 100W incandescent bulb puts out about 1600 Lumens, but LED downlights that say they are "100W-equivalent" typically say they are 850-1100 Lumens. If I wanted to switch from 200W (3200 assumed Lumens) incandescent lighting to LED downlights, do I buy two "100W-equivalent" lights even if they say they only total 1700 Lumens, or do I buy four 850-Lumen downlights because they total 3400 Lumens, which is close to 3200 Lumens?

If it matters, it is a residential application; I am looking at 2700-3000K LEDs.

 

[Steve123]

You need 4 850 Lumen bulbs to match the light output of 200W incandescent.

However, note that LED bulbs are frequently more directional than the old incandescents.

 

[bud16415]

There is also the Helmholtz-Kohlrausch effect that both plays into how these lamps are rated and how bright they may appear. If you want to know more about that effect you can google the name.



What I do is substitute them based on the equivalency rating shown on the package and I have not been disappointed, and in most cases I feel the LEDs seem brighter.



When I switched the 4 ceiling floods in our kitchen I felt they were too bright at first but quickly got used to them.

I love the lower power consumption and the reduced heat. The last batch I bought were $1 per lamp for the regular shape bulb and $2 for the larger floods. I just wish we made them here in the USA like we made the old bulbs.

 

[Jeff Handy]

Whatever you do, only buy warm white approx 2700-3000 kelvin LEDS for most home use.

The bright white 5000 kelvin LED light is so harsh and unnatural, yet I see people putting it everywhere.
It is like horrible office or hospital or industrial lighting.

It is ok for a garage or unfinished basement utility lighting, but nowhere where you actually spend time with it

 

[bud16415]

Sunlight is around 5500 k and we are used to it when outside. We are also accustomed to soft white incandescent inside at around 2500 k.



As I mentioned above going from soft white to LED white in my kitchen ceiling lights was a bit of a shock. It is also something we surprisingly grew used to quickly in the kitchen as it mimics daylight quite nicely and the apparent lumen improvement seems greater based on the H-K effect. In a kitchen we want true light and it is a good thing. Now in the living room lamp the warmer temps really seem to warm the room and have a different effect.

More and more if it is task orientated lighting I like the neutral 5500 k light.

 

[ajaynejr]

Roughly the lumens conundrum and lumens discrepancy is due to the directional nature of LEDs. For the LED downlight the rated lumens should be what comes out downward. For a typical incandescent lamp the lumens rating takes into account the light going in all directions. Much of the light, maybe 50% in some cases, is absorbed before it can come out the bottom of the can light fixture.

The absorption can be worse with long tube fluorescent fixtures. The tube itself shadows some of the light that went up and bounced back down by the reflector above. Frosted incandescent bulbs also shadow some of the light captured and "saved" by fixture eflectors.