High-current, small area, low efficiency, expensive LEDs. Why? - Page 1
Forum section: electronics / projects

author: Artlav
author_rank: Frequent Contributor
timestamp: November 22, 2017, 03:39:21 am
content: I've been browsing Digikey recently, and came across this series of LEDs:https://www.digikey.com/products/en/optoelectronics/led-lighting-cobs-engines-modules/111?pv684=248&pv684=247&pv684=307&FV=fffc04be%2C33c01eb%2Cffe0006f%2C1f140000&stock=1They come in R,G,B separate colors and as white, they are in a high-heat-dissipation packages, they work at 4V and tens of amps, they are about as efficient as incandescent lightbulbs and they have small emitting surface area.Oh, and they cost an arm and a leg.I'm a bit confused as to what can these be used for. Datasheets list innocuous things like entertainment, general illumination, projection and so on, but nothing that stand out.And yet since they exist and are expensive i suppose there should be some sort of a niche where they make sense.Anyone have any ideas?

author: Someone
author_rank: Super Contributor
timestamp: November 22, 2017, 03:59:32 am
content: Your link points to the assembled modules for installing into equipment, the bare packages are cheaper (but still expensive) and list more detail:http://www.luminus.com/products/Luminus_SBT90_Datasheet.pdfThere are optical reasons to have a small emitting area and they have a good lead in luminance (lm/mm2) over competitive products.

author: Sceadwian
author_rank: Unknown
timestamp: November 22, 2017, 05:46:15 am
content: Quote from: Someone on November 22, 2017, 03:59:32 amWhat is that good reason for small emitting area? I find it amusing as well as unbelievably frustrating when people say there's a good reason for something and then omit describing it.

author: ruffy91
author_rank: Regular Contributor
timestamp: November 22, 2017, 06:02:37 am
content: Reflex sights, light barriers, projectors, everywhere where you need a point light source.It's more efficient to have a smaller light source than having a bigger one and using a pinhole aperture which blocks 99% of the light.

author: Someone
author_rank: Super Contributor
timestamp: November 22, 2017, 06:44:00 am
content: Quote from: Sceadwian on November 22, 2017, 05:46:15 amAgain, its right there in the data sheet if you read the first page applications:"High output, Etendue-limited lighting applications"I'm not here to teach people the basics of optics.

author: dmills
author_rank: Super Contributor
timestamp: November 22, 2017, 12:03:39 pm
content: Basically many optical applications need something that approximates a point source, the closer the better (Because it makes for an easier, cheaper and more efficient optical system.For example in a projector you need close to a point source illuminating the image plane because anything else will result in a blurry image. You can approximate a point source by means of distance, condenser lenses, pinholes, and various other things, but they all add cost and rob you of efficiency, starting with a small source is always going to be best.There is a reason the old cinema projectors used carbon arc and later xenon arc lamps, and why modern video projectors use UHP mercury arc lamps all of which have notably small emission areas.Regards, Dan.