Below my notes is a (lightly edited) response from my friend Ken who is undertaking a crusade to locate the Holy Grail of LED MR16 lighting - and so has some useful things to say about the more easily replaced PAR38's Cree have provided a reference design which exceeds energy star specs for a 150 Watt PAR38. PAR38s come in 100 120 150 W Halogen versions (maybe more) and lower Wattage specs are easier to match. Cree chose to use their MT-G2 multiple die LED. This is an <=3D 18.5W part but the spec sheet efficiency and output ratings are all given at about rated at about 7 Watts in. Efficiency Output at that level is about 120 l/W for the flux bin sample chosen. Slightly higher is available. Lower when run at full cry as in this design. They chose a "std CRI"version which can be had at CCTs of 2700 3000 3500 4000 5000 K with up to 20% more flux in 5000k versions. You can get 80 CRI versions at 4000 & 5000 K with same flux or better than their reference and 90 CRI at 2700 & 3000 K with somewhat lower max flux. Given your spec, if using this basic design then the 5000k 80 CRI N0 bin gives close to the best of all worlds. Datasheet here https://www.google.co.nz/url?sa=3Dt&rct=3Dj&q=3D&esrc=3Ds&source=3Dweb&cd= =3D2&ved=3D0CCYQFjAB&url=3Dhttp%3A%2F%2Fwww.cree.com%2F~%2Fmedia%2FFiles%2F= Cree%2FLED%2520Components%2520and%2520Modules%2FXLamp%2FData%2520and%2520Bi= nning%2FXLampMTG2.pdf&ei=3DdrfFVIe6IKO8mAWm4oKABA&usg=3DAFQjCNGr6OgCwsgmkhi= 3eypkGyosgqCAQA&sig2=3DaRk0ptS_5NLDUi8QpPu5lw&bvm=3Dbv.84349003,d.dGY&cad= =3Drja Product page here: http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Arrays-Direct= ional/XLamp-MTG2-EasyWhite Ken mentions two now non-attached attachments. If you want and cannot easily find these email me offlist and I'll send you copies Russell Ken said: My principal interest has been with MR16's - which are a much harder ask for the LED lamp manufacturers due to it's very small form factor (compared with other main-steam incandescent bulb types) and generally poor cooling of the luminaires in which they are typically used. Compound this with the huge number of "junk" MR16 LED replacements coming out of China which typically have 1/2 to 1/3 of the claimed light output, are often physically longer than the MR16 standard allows, tend to be fussy about the characterics of the low-voltage "transformer" supply they are driven from (especially if dimming is required), and often overheat (such that they become thermal relaxation oscillators) - you will understand why I have a somewhat jaded view. Cree offer a true solution (their LM16) but they only manufacture in small quantities for the US market and it is difficult to source here and prohibitively expensive for large-scale retrofit. Philps come close (but their bulbs have a fan in them). The PAR38 should be easier - although 150W is perhaps approaching the same power density as a 50W MR16. A standard 150W PAR38 incandescent from a name-brand supplier (GE, Philips, Sylvania, etc.) should output something in the region of 1800 to 2400 lumens - so between 12 and 16 lumens per watt. New halogen incandescent incarnations (especially those designed to provide efficiency gains) will generally have a similar light output but at a lower input power - with luminous efficacy up to 25 lumens per watt. Cree (arguably at the forefront of what is possible in terms of white LED technology) provide a number of reference designs for LED-based PAR38 lamps - including this one which covers a dimmable 150W-equivalent design (although for 120VAC mains input): http://www.cree.com/~/media/Files/Cree/LED Components and Modules/XLamp/XLamp Reference Designs/XLamp_MTG2_PAR38.pdf As you can see there is no real "rocket-science" in it - just application of good engineering practice with careful choice of appropriate components and a modicum of optimisation using appropriate software tools. For this reference design Cree manage around 1277 lumens at power input of 21.6W giving a luminous efficacy of 60 lumens/watt. The light output is quite a bit down on a 150W halogen PAR38 (being much closer to the 1500 lumens typical of a 100W unit) - but the power input is only around 14.5% of 150W - and the expected life is around 15 times longer. Cree do not appear to manufacture or market the end result (and if they did it would probably be expensive and not offered outside the US) - but there is no reason at all that other manufacturers could not produce an LED-based PAR38 bulb of similar performance. The problem will be that only a handful of reputable manufacturers will produce such a bulb that is true to spec and offers the reliability (and hence lifetime) that could reasonably be expected. I have attached the relevant page from Philips lighting catalogue (for 2013). As you can see, they are quoting 1200 lumen output for 19.5W input - which is a tad better than Cree achieved in their reference design - but still fair way away from the output of a typical 150W PAR38 incandescent. I have also attached a relevant datasheet from GE. They are offering an 18W unit with 1300 lumen output - which is much the same performance as th= e Philips product (but only for a color temperature of 2700 =B0K). I do take some exception to their claim that their 18W LED PAR38 is equivalent to a 120W incandescent PAR38 (as the raw numbers say otherwise) but there are a lot of subjective factors at play (including colour temperature, the spatial distribution and off-axis spill, etc.) that can influence any comparison. My advice is to look at the datasheets for mainstream manufacturers offering such bulbs and make your choice accordingly. Buy one and try it in your actual application (especially if a dimmable bulb is required). You would be well advised to stay away from unbranded Chinese bulbs (as even when a data sheet exists it is usually a thinly-disguised copy of one from a reputable manufacturer and bears no resemblance to what the vendor is actually selling) as they are very unlikely to give the light output claimed and are likely to have short lifetimes for one reason or another. If you are really keen to "do it right" get a decent light meter and take careful readings with the original incandescent bulbs in place and then with the proposed LED replacements. So in summary - I think you will struggle to find an LED-based replacement for a 150W PAR38 incandescent that has the same lumen output - but there are certainly products out there that would give quite good performance if you can tolerate some reduction in brightness. You could go for LED bulbs having a slightly higher colour temperature (say 3000 or even 4000) as subjectively these will appear brighter - but you will probably need to be content with a CRI in the low 80's. If you really want the same light output I think your only real choice will be to abandon the idea of using an LED-equivalent of a standard form factor incandescent bulb and instead look at complete luminaires designed specifically for LED's - but your cost will then be much higher. Regards, Ken Mardle -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .