Lumens per watt for Edison-socket style LED light bulbs

I always find it interesting (and discouraging) to calculate the lumens per watt of the current crop of LED bulbs that are available from most big box stores these days. I find that they generally hover in the + or - 50 lumens per watt range. This is often no better than the CFLs on the market on the shelf right next to the LEDs (at a fraction of the price). I realize that the LED lights are often superior to CFLs in other ways but light efficiency is important to me. Now, I understand that they are not typically using the latest generation of LED emmiters in the consumer light bulbs, but my question is this. . . what do you figure the LPW figure range would be on a drop in bulb replacement that used the latest XML emmiters (I'm assuming that that is the best out there), factoring in the inefficiency of conversion from AC to DC as these fixtures require (as opposed to battery powered flashlights)?

Based on your observation of the market, how long will it be until the current XML emmiters become reasonably available in these types of bulbs?

Thanks for your thoughts.

Not much better if you want decent brightness. The Edison socket is outdated. It's built for 1000+lumen devices that are tolerant of heat. LEDs are not tolerant of such heat, and need large radiating areas for cooling. Enclosed fixtures (And most light bulb fixtures) further waste 40% or so of your output.

LEDs are efficient at low current. But LEDs are expensive per unit, and to get high brightness cheaply requires running them hot. Dissipating heat requires large heat sinks or active (whirring) cooling. And still can't happen in enclosed fixtures. LED retrofits are not the way to get good lighting.

Purpose-built LED fixtures are the way to go for better efficiency. I get about twice the effective light from my 12W light strip as I do from a 23W CFL in a fixture. It's just two 12V LED strips on an aluminum bar, behind a valence (That glows nicely now). Cost me maybe $30 and some time to wire it. I expect to move with it after this job in VA.

FloridaGuy said:

Based on your observation of the market, how long will it be until the current XML emmiters become reasonably available in these types of bulbs?

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Current XM-L emitters? Probably never in an "incandescent replacement" application - too expensive and not rugged enough.

A new product with performance similar to the XM-L? Once the manufacturers can cut costs and "ruggedize" dies with levels of performance that can withstand the thermal and longevity requirements of the "incandescent replacement" environment.

As AnAppleSnail has mentioned - purpose-built fixtures will achieve superior performance and longevity since they can be built to deal with the heat and offer far better optical performance.

A front that few pay attention to is low-power SMD LED's. These can be deployed in parallel with fewer thermal considerations with similar Lm/W and Lm/$ relative to the sexier high-power LED's. I gather that their present limitations are quality-related - consistency and operating lifespans.

The XM-L you are probably thinking about is unsuited for home incandescent replacement.
It is too blue, makes my bread look moldy when it is not. Warmer tints are available but you lose up to 30% efficiency.
In a flashlight an XM-L would be run for 300 hours max per year. In a home bulb it can be on for 8760 hours a year. So in an LED bulb the LED can NOT be overdriven at 2.8A. Cree recommends 0.7A. So instead of 800 lumens at 6500°K you get 240 lumens at 2700°K.
It is the wrong voltage at 3.3 VDC. Household circuits are 115 VAC which converts to 171 VDC.

Cree has a high voltage version of the XM-L for fixed lighting use. XLamp XM-L High-Voltage White. 46 V @ 44 mA. 3,700 – 2,600°K. 172 lm - 182 lm. (Note it is less than 1/4 the lumens of the XM-L in your flashlight.)

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Philips have the L-Prize winner - 940 lumens from 10 watts but its current list price is $60.
2 other companies have announced they will enter the competition. When their bulbs hit the market the competition will force prices down.

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The Lighting Facts people have a database of all the LED bulbs that have applied for a Lighting Facts label.
You can search for the most efficient bulbs there.
http://www.lightingfacts.com/products
(The database does not seem up to date - the Philips L-Prize winner is not in the searchable database yet but has a link to its info page from a button in the top right corner.)

Based on your observation of the market, how long will it be until the current XML emmiters become reasonably available in these types of bulbs?

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Never.

Retrofit LED bulbs have two main issues; heat and price. The best way to alleviate heat issues in a typical Edison style retrofit is to use smaller LEDs, and lots of them no bigger than 1watt each. This allows heat to be distrubuted more evenly and not require such a bulky heat sink with a dense core to absorb thermal from a single LED. While the XM-L might be more efficient at even a couple amps the difference isn't big enough to warant the extra heat-sink cost.

Diffusion is another issue. Much easier to diffuse several clusters of lower powered SMBs than 1, 2 or 3 XM-Ls. Obviously the XM-L wins if you want a tight, controlled light source, but that's not the market we're talking about.

Last is price. You can buy custom, high performance PAR 38 packages that use XP-Gs or XM-Ls. Some of these easily exceed 90 lumens per watt in warmer colors and 120 lumens per watt in cooler colors. Obviously with a PAR 38 package you have a pretty robust heat sink to work with -vs- A style retrofit. However, these PAR 38's tend to cost upwards of $100, but are in a different class entirely than the typical big box fare.

Looking at the latest Caliper tests from the Dept of Energy LED retrofits are slowly creeping above 60 lumens per watt in warm white as a mean product group. This is better than CFL

The 13 watt rated CFLs ("60w equivalent") are spec'd to about 63 lumens/watt.

In a screw in bulb, yes XM-Ls won't be very efficient. However, I have seen them start to creep into the motion sensor outdoor flood lights. Home Depot had a two head one for $90 that put out 1700 lumens at 21 watts. This is the perfect application for XM-Ls. They are purpose built, are used outdoors were it will be cooler, and aren't on long enough to heat up. They are instant on at full brightness unlike florescent (which suck in the cold and take never get to full brightness on a motion sensor) and are way more efficient than halogen.

I saw the same lights at Home Depot and was impressed at their brightness. As long as XM-L's are heat -sinked correctly and you don't mind a single point light source they make logical sense in this package.