The CREE cool white XP-G series datasheet is out. Color temp between 5,000K and 8,300K and a CRI of 75. Would these work for reef lighting in combination with some royal blues?

This is the same CRI as the XP-E series cool white however their datasheet listed the color temp range from 5,000 to 10,000K.

Sure you can use them. Keep in mind that they will need different optics than the XR-E, and won't be shipping until later in October.

Do these get the evil seal of approval, do they look like a huge leap from the XR-Es we're using or is it too soon to tell? I guess i'm really just asking if you're excited about them?

If you need more light than the XR-Es can provide, then they are great. Considering that they have only been on the market for a little while, it's hard to tell just how usefull or cost effective they will be compared to the XR-Es that we all know and love.

The big advantage of these is not when compared to the XR-E, but the XP-E/C. the XP-G is higher luminous output per watt, and can be driven at a higher current. You can basically abuse these the same way as the XR-Es.

Some interesting info (XP-G vs. XP-E) based on actual test results over on candle power forums

http://www.candlepowerforums.com/vb/showth...607&page=12

'scuse (XP-G vs XR-E)

XR-E Q5 @ 1000ma, 3.50v: 237 lumens
XP-G R5 @ 1000ma, 3.26v: 351 lumens

Depending on lenses etc it should be possible to replace 3 XR-E Q5's with only 2 of these and it will run significantly cooler at that.

...nothing new from Cree for two years and now this like a week after I build my LED fixture

Im hoping for an MC-G. I have time to wait....

I'm just waiting for them to make one big damn LED that's like 100 watts that you can boil your clams under and whip the dudes running 250 MH's.

There are 100W LEDs, but they are very inefficient.

Geez, couldn't imagine the thermal issues something like that might present.

it turns a heatsink into a hot plate...

the R5 bins seems too good to be true.. glad i waited for them to come out
time to wait some more for the price to drop =p

too bad they dont have the blue leds out for it yet...

These new LEDs are under 1/5 the footprint of XR-Es; you could make a 100w array of 30 of these fit in a 1" x 1.25" area with realistic spacing. If you can get the thermal impedance low enough it would run cool on one of the massive computer processor heatsinks they make now. That's a big "if" though, but it sure would be fun to play with

...until the police show up because you are blinding airplane pilots.

Could you imagine an array like that with a nice aspheric lense over it? You'd be damn near burning holes in stuff

Would there be enough infrared to do that? I'd always thought the magnifying lens+sun=fire trick was from the IR the sun put out being concentrated/focused to a point, the visible spectrum just there for show. I may be way wrong though.

It's more a concentration of energy than a concentration of IR. There have been many people that have been able to burn paper with LEDs and lasers.

True that, had forgotten about a friend of mine had a little green laser pointer, he was able to pop black balloons and set fire to black paper with it pretty easily.

I lol'd.

So where is the best place to get the Cree XP-Gs. So far the only place I have seen them is on Cutter.

$5.50 per led isnt that bad, how low are you guys waiting for it to go?

$5.50 sounds great to me but if you get the R5 and throw in a star it is around $6.90. Still not horrid but if I can get it cheaper somewhere else why not.

Haven't seen them anywhere but cutter, I did send rapidled.com an email and they said it would be a couple of months before they are stocking the XP-G.

Just reread this and while the output is impressive this would also mean you could run 14 XP-Gs on a meanwell insteard of the 13 XR-Es, right?

why yes

mmmmmm, these would be perfect for the 20L I'm planning. This way I could run more reds, greens, and UVs. My LFS bought some cheap LEDs for the fish tanks, and the different colored LEDs really make certain colors pop. I want to try the same thing with higher power to see if coral colors pop too.

Not really. You have to remember that the quantity of LEDs is there for coverage, not intensity. What the higher output LEDs will let you do is reduce the need for lenses, or get the same output for less current when compared to XR-Es.

but thanks for the clarification.

So if you reduce the need for lenses, you get greater spread at the same intensity. Doesn't that mean you can spread your LEDs out and use less LEDs?

Just to clarify, by same intensity I mean you get the same (or similar) intensity with a XP-G without a lense as a XR-E with a lense.

Yes, but the difference is minimal. It may mean you can save a few LEDs when going from a 2" spacing to 2.5". It really will only affect the LEDs on each row, as you will want to keep the spacing between each row to no more than 3".


Approximately, yes. It's not going to be to the same level as an XR-E with a 60 degree lens, but close to an 80 degree lens.

why dont they just give us the 683lm/watt leds already...
=)

dont mind running 1 or 2 of those in my 20g.

I've been thinking about doing some changes to my pico LED light so I've been reading more about these and noticed this:



Looks like the XP-Gs have a substantially wider output than the XR-Es and might be more useful than previously thought. If the increase in output is large enough that the wider pattern is lit to the same level as the XR-Es then maybe these can in fact be used with wide enough spacings that they become cost effective?

I dunno, but as soon as these hit dealextreme or somewhere where I can get a pair without half my total being shipping I'm going to try these out.

edit: I'm mostly referring to pico/shallow applications where XR-E's with no optics are plenty intense and the limiting factor for LED spacing is the dispersion angle. Should still help by allowing wider lenses at similar intensity levels though?

You could get a little extra spacing. Won't be much though. The better emission curve is from the larger die that the XP-G uses.

I'm loving this thread. I got an email from Cutter saying that the bins 1B, 1T, 1C are now available (1B being the highest, being just over 6500K on the graph. I'm not quite sure what the difference would be between the 1B, 1T, and 1C (they are all near 6500K).

Anyhow, we may well see them come out with some blues. If this critter really is the cat's meow, they oughta be working hard on it.


I found out the other day I live literally 25 minutes from a Cree factory. Unfortunately I don't think they give tours or free samples

I just sent Cree an email asking if they were going to offer, anytime soon, a royal blue XP-G or even the big MC-E.

EDIT -Sorry guys - It was a long day and I wasn't thinking. I stand Corrected.

Chris

Remember that light must follow snells law, and as such, any light at an incident angle that is more than about 48.6 degrees gets reflected by the surface of the water. That means the maximum useful bare emitter is about 96 degrees.

All that other light needs to be reflected so that the light outside of 48.6 is used. Look at how much is lost by the XP-G sans secondary optics, the steep nature of the XR-E means light is delivered more efficiently when optics arent considered.

http://www.school-for-champions.com/scienc...ction_snell.htm

If you are a real light junky, you would design your tank to exploit TIR (Total internal reflection) by having sloped walls.

I witnessed this firsthand at MACNA Atlanta. Coraldynamics had an LED light which read 20-30% more in water than in air. My explanation was that he was using a cambro, shaped like \__/ and that caused added internal reflection.

Chris

PS - for ease of use, draw a vertical line at 48.6 and thats the light you will be getting delivered.

XR-E for ME!!!

Chris

The example is from a relatively slow speed high index material (water) to a higher speed low index material (air). Credit below to Argonne National Labs and Dr. Mellendorf:

Question - Is the critical angle for light going from air to water
the same as the critical angle for light going from water to air?
-----------------
David A.
A critical angle exists only for light passing from a slower-speed medium (high index of
refraction) to a faster-speed medium (low index of refraction). When going from water
to air, there is a critical angle: sine of the critical angle equals 1/1.33. When
going from air to water, the sine of the critical angle would have to equal 1.33/1.
Since a sine function cannot be greater than 1, there is no critical angle.

Dr. Ken Mellendorf
Physics Professor
Illinois Central College

For a visual demo check out
http://interactagram.com/physics/optics/refraction/
Figure 3 is interactive and pretty interesting.

If you were planning on using 80 degree optics anyhow, this wouldn't matter

It doesn't matter regardless of optics vs. no optics, provided you are going from air to water (the critical angle, 48.6 degrees from vertical, is not applicable in this case).

I think jtl2 is correct. Total internal reflection doesn't occur when light is passed from a medium of lower refractive index to one of higher refractive index. Sloping the walls of a tank will not enhance total internal reflection either because glass has a higher refractive index than water and therefore light passing from water to glass cannot produce total internal reflection. That being said, normal surface reflection from water/glass can still occur.

You get higher PAR with water in a tank because normal refraction is causing light that normally would escape through the tank walls when no water is in the tank to be bent such that the angle from vertical is smaller. In other words, the prescence of water causes the light to be bent "in" to the tank.

Scott

So basically you're saying that the water column refracts the water in such a way that it acts somewhat like a reflector, anyhow?

I remember in physics in college studying the refraction of light, but I couldn't recall if it narrowed or spread out the projection pattern of a point source of light.

A lot of different things going on when light enters the water: refraction, scattering, absorbtion, etc... I was just pointing out the refraction of light from air to water. Again, Figure 3 on the referenced link above gives a great interactive demo, just move the flashlight to different angles to see the refraction effect when going from air to water.

You can also adjust properties on Figure 3 to put the light source in the water (change properties of the top substance to water and the bottom substance to air, just opposite of where our light sources are...for the majority) and you can see Snell's Law and the critical angle.

Sorry for the bad info. It was a long day and I posted without thinking too much. I stand corrected.

Chris