# What's the problem in designing a bright enough LED lamp?

So far the most powerful household LED lamp I've seen had consumption of 2.1 Watts and gave light equivalent to maybe 15-25 Watts incandescent lamp. That's maybe good for illuminating a Christmas tree, but totally unusable for using as usual lighting - too dim. The situation hasn't changed over the previous three years - I see more models on the market, but they are still very dim.

Is there some design problem in creating a more powerful LED lamp?

• Yea i agree- i bought about 20 LED bulbs for testing and changed my workshop room to use these. Its nice and white but with a ceiuling height of 1.8Metres- i could not see properly- when used in a table lamp- 30CM height- it works great! .. Maybe a better option is to use a SUPER BRIGHT LED Strip that has condensing lenses on them and not just bare ones! you know the ones that look like they have bubbles on them ;] – Piotr Kula Jun 9 '11 at 8:05

The problem here is one of scale.

The way an LED works is that the electrons jump from the N side to the P side of the semiconductor junction, and as they do so some of the electrons fall into 'holes' in the P side. This changes their energy level, and causes the discharge of a photon - ie, light.

This means that:

• The junction is very small, so the amount of light emitted is limited.
• Because the light comes from a very small area, it casts very sharp shadows.
• As the light diffuses the 'quantity' of light in any one area drops massively, so what is bright in a tiny spot is dim in a large area.

Yes, you can have multiple LEDs in a 'bulb' to give a larger amount of light, and to provide a more diffuse shadow pattern, but still as the light diffuses it gets very much dimmer. It then becomes a problem of sheer bulk - trying to get enough LEDs into a small enough area to give enough light at a reasonable distance.

That is why they work OK in a table lamp at close range, but at longer range (the ceiling) they are next to useless.

There are 2 main issues, price & heat.

1) 1W LED of high quality costs somewhere between 1 and 3$. So for 20W you should be ready to spend 40$ just for LEDs, and some 15$at least for constant current power supply. +you need decent heat sink to dissipate 20W. So, base cost goes somewhere to 80-100$. How many people can afford to spend 100$on lamp (provided that it's lifetime is not infinite - LEDs does degrade, especially at elevated temperatures)? 2) Incandescent lamps can work at 200C, luminescent - at 100, but you really need to keep LED's below 50, or they would die young (and it's much harder because they have much smaller case). Active cooling would be great, but it's more mechanic hassle & not many users can tolerate that. This is the reason I am going for metal-halide lamps for home lighting instead of LEDs - they are better than LEDs in many ways (including power efficiency & light quality) • You can get Cree XM-L EasyWhite 12 or 6V varieties for$8 each. they are 13Watt LED modules with many emitter die visible in them. Obviously they internally series + paralleled emitters. The end result though is really awesome. I made a 3KWatt strobe LED array pumping 120 Amps into it (an array of 48 Cree XM-Ls) for 5-10ms periods, at 10-16Hz. It was amazing. ~70K Lumens haha! – KyranF Apr 8 '14 at 1:47

The limited variety of LED light bulbs on offer down at the convenience store is due to basic market factors, not so much to technical limitations. The average consumer prefer to buy a light bulb that lasts 1000 hours for 1 dollar compared to a 20 dollar light bulb that is promised to last 50.000 hours.

LED lighting is used for a lot of 'big lights': street lights, industrial lighting, stadion lights, etc. LEDs are not limited to table lamp use.

LEDs dissipate less heat for the same amount of light compared to most other alternatives. The luminous efficacy of a modern LED is now over 100 lm/W, while a tungsten bulb is under 20 lm/W. Fluorescent lighting is about 60-80 lm/W.

It is a bit imprecise to say that a LED casts a harder light than, say, halogen. The hardness of light is defined by the relative 'size' of the light source to the subject. The sun casts a very hard light. The sun is big, but it is also very far away, so light rays from the sun appears to be parallel. The size of a LED emitter isn't that different from a halogen wire compared to the distance and size of the subject you are illuminating. Many light fixtures are designed to enlarge the apparent size of the emitter (using reflecting and diffusing surfaces) and thereby cast a softer light. If you want softer light, don't use a spotlight, use a different kind of lamp.

The first white LEDs had a godawful blueish tint. Nowadays you can get much better light quality and lower color temperatures. Still, the spectral composition of LED light is not as good as a black body radiator like a incandescent bulb (or the sun). Many people, myself included, like that light quality.

A 12 W LED, equivalent to a 60 W incandescent: