# LEDs for full daylight

I'm working on making a sign that will be outdoors in full sunlight and I want it to have the longest range visibility.

This is a project for university and I will probably need 100 LEDs or so - I need the cheapest possible but I really want people to be able to see it from afar!

• Only 100 LEDs? That's only a 10x10 grid...you can show like 2 or 3 letters only, not a whole lot of info. – davr Nov 19 '09 at 22:30
• It isnt going to need to show letters....just symbols X O -> thats sort of thing. The major project is to do with traffic flow etc so this is just a cool little demo we want to set up – SaM Nov 19 '09 at 23:54
• From the two previous answers, I'm guessing the question is "can anyone recommend a source for these LEDs", but it's usually a good idea to make that kind of thing explicit :) – edebill Nov 20 '09 at 3:40
• I'm disappointed that I don't see any answers that say how many lumens a LED needs to be visible in sunlight. How do you get the 2,000 cd/m² you need to be sunlight-visible? I'm also disappointed that none of the answers mention what to put around a LED to increase on/off contrast in sunlight -- things like the visor that casts shade on a standard traffic light, or various colored filters and light traps. – davidcary Mar 7 '11 at 4:29

SuperBrightLeds.com have a wide variety, at least. I haven't bought from them much, but they have LEDs in pretty much any size and output you'd want. Make sure you pay attention to viewing angle as well as output power - for a sign you probably want something with a wide viewing angle.

The super bright white LED may be a good bet, only 20 ma or so to light.

I've had good luck with ledshoppe.com. 100 5mm super-bright LEDs them should come in around $5-$8, shipping included. They can take a couple weeks to arrive (they ship from Hong Kong or Taiwan), but all 3 orders I've done with them have arrived reliably.

I'd suggest buying some extras - for only twice as much you can get 200 LEDs and have plenty of extras in case you toast a few along the way.

If you want to go a slightly different route, you can buy LED fixtures from Philips Color Kinetics (www.colorkinetics.com). They make string lights ("Flex" is the name of the series), and you can talk to them using one of their power supply/controllers via Ethernet or DMX (an RS-485 based protocol). Its an option rather than hardcoding it yourself. You could then mount the Flex lights how you want them. They should be bright enough to see far away in daylight. Just another option...

To be seen from a long distance you have to compromise.

Increasing visibility from a single point or a certain direction is possible by reducing the angle of radiation without adding a huge amount of power. The narrower the cone the radiation is confined by the housing of the LED the more power will be directed to the eye of the beholder. This works well if your sign has to be seen from a linear road, i.e. if beholders follow a certain path approaching the sign.

Another method to increase visibility without investing lots into high power LEDs is to increase contrast by surrounding all LEDs with dark non-reflective matter like cardboard with black paint.

These are methods which do not depend on the progress of LED production in terms of power and efficiency, so I dared to add them to this old question.