LED Matrix Displays and Daylight - Page 1
Forum section: electronics / projects

author: mc
author_rank: Regular Contributor
timestamp: June 01, 2013, 02:13:45 pm
content: Has anybody got any experience with LED displays that are viewable outdoors in daylight?I've already made a couple using the 5mm bi-color led matrix boards from Sure-electronics, which are perfectly fine for indoors, but in daylight they are pretty much useless.I know I need more Lumens, but my googling so far has drawn a blank on how many, although I'm guessing how many lumens is quite an open ended question with lots of variables, so I'm essentially looking for some pointers as to where to start.I'm not afraid to spend reasonable money on this, provided I know I'll get a workable solution at the end, but I don't want to waste money on something that may not work. I'm guessing I'll have to go for custom PCBs with individual LEDs and associated drivers/control circuits, but I really need to find some suitable LEDs as a starting point.I'm not bothered about having bi-color, and I've not totally ruled out going for electro-machanical modules, however I'd like the versatility of a LED matrix.

author: Paul Price
author_rank: Super Contributor
timestamp: June 01, 2013, 03:31:13 pm
content: If you use your hand and/or by making a red gel filter(dark red transparent plastic) fit over the display you can easily see red leds in the sunlight.

author: mc
author_rank: Regular Contributor
timestamp: June 01, 2013, 04:14:11 pm
content: Already tried that. For the existing displays, I actually settled on frosted grey perspex after trying various combinations.The big issue is the displays just aren't bright enough to compete with sunlight. They are visible, but not at a distance.

author: Baliszoft
author_rank: Frequent Contributor
timestamp: June 01, 2013, 05:32:54 pm
content: Build up your own matrix using high power leds (5mm is dirt cheap).

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: June 01, 2013, 06:38:15 pm
content: I take it you did try a RED filter ?? as in thick dark RED, thin light RED acetate wont' work. You'll find on test equipment they use dark thick RED plastic/perspex

author: Corporate666
author_rank: Unknown
timestamp: June 02, 2013, 01:38:02 am
content: A gray lens is a bad idea, gray will block all colors of light, so all it does is make your display dimmer.Use the same color lens as your LED color. As said above, a dark red lens over red LED's will block everything except red light. The difference between a dark red and gray lens is huge.Also, as you said, it's about lumens. I made a display about 35 x 10 'pixels' using Kingbright LED's - for red, I used thishttp://www.digikey.com/product-detail/en/APG1608SURKC%2FT/754-1359-2-ND/1919167Multiplexing 10 rows, I drove them at 200mA and 10% duty cycle. But with 35 columns, that is 7 amps continuous. At about 2.5 volts per LED, it's over 17 watts. That is a TON of power and it was bright. Really bright. Easily viewable in the middle of July at noon with direct sunlight overhead.At high wattages, you also want to get the most efficient LED's you can so heat will be less of an issue.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 02, 2013, 11:45:05 am
content: White matrix displays can be bright enough to be pretty readable in high light levels, but more expensive than standard colours.For colour dispays, some filtering, and anti-glare coatings can help a lot.QuoteYou can get circular polarizing filters, which look grey but can can improve display visibility.

author: Corporate666
author_rank: Unknown
timestamp: June 03, 2013, 03:17:55 pm
content: Quote from: mikeselectricstuff on June 02, 2013, 11:45:05 amI haven't seen polarizers used on colored LED's before - have you? Are they more effective than just a colored plastic lens?The OP mentioned he used gray perspex, which has the look of a polarizer, but not the function... I haven't actually seen polarizers used on colored LED's though... I wonder if it's a cost thing or they are less effective than colored plastic?

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: June 03, 2013, 04:09:46 pm
content: 3M makes a material called light control film. For LED displays used outdoors in sunlight, it is awesome.Think of Venetian blinds that are completely open. If your look straight through, you can see clearly with almost no interference. When you look through at an angle, you can't see through at all. With light control film, you can see directly through, but if you position the display so that the sun hits at an angle, it's blocked and doesn't wash out the display. I've used it effectively with relativity dim LEDs in direct tropical sun with good results."Film" is sort of misleading. The stuff I have used is rigid plastic, somewhere between 0.5 – 1 mm thick I'd guess and looks gray like a polarizer. It works well with all colors of LEDs. The downside is the stuff is relatively expensive. Back in the dark ages, I had it cut with a water jet, but it should cut beautifully with a laser.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 03, 2013, 04:50:52 pm
content: I think the idea of a circular polariser is that any light that comes in and is reflected off the surface of the display has its polarisation flipped and so doesn't come back out - I think I used it on a clock I made a long time that used EL backlight panels which were white when unlit & it made quite a difference.

author: mc
author_rank: Regular Contributor
timestamp: June 03, 2013, 06:11:15 pm
content: Cheers for the suggestions/comments.The shade of grey I used was selected after trying various samples, and it works well indoors. It does block some of the green, and has a marginal effect on the red, but is a vast improvement over nothing in terms of legibility in anything other than darkness.I did wonder if a polarizing film applied directly to the matrices would be more effective, however having seen a LED matrix display in use outdoors yesterday, the LEDs were definetly far brighter.Looks like I'll have design something from scratch to get something suitable :-/

author: Rufus
author_rank: Super Contributor
timestamp: June 03, 2013, 08:51:57 pm
content: Quote from: Corporate666 on June 02, 2013, 01:38:02 amBecause reflected light passes through the filter twice in makes the display dimmer and reflections twice as 'dimmer'. You trade display brightness for increased contrast which can be worthwhile.Polarized filters make reflections more than twice dimmer and are even better.

author: Corporate666
author_rank: Unknown
timestamp: June 03, 2013, 10:37:48 pm
content: Quote from: Rufus on June 03, 2013, 08:51:57 pmBut the ambient light level is so much higher than the display brightness (in sunlight) that even though you may increase the relative contrast, you end up losing too much brightness overall. I've never seen a gray lens used in place of a colored one, at least... maybe some do it? But in the tests I've done, we got much better results from a colored plastic lens than gray.

author: David_AVD
author_rank: Super Contributor
timestamp: June 04, 2013, 12:50:25 am
content: In my experience, a diffuser of the same colour (of the LEDs) is better than a grey one. For multicolour displays, a clear plastic with non-reflective coating (on the outer face) is the best you can do.Of course all of that is useless if the displays just aren't bright enough. The sun is one hell of a light source to compete with!

author: Corporate666
author_rank: Unknown
timestamp: June 04, 2013, 02:11:32 am
content: What about Mike's idea of a polarizer on a multi-color display? It would seem that it should work to allow light to emit from the display but prevent polarized light (that got in and bounced off something) from getting back out.On the other hand, the circular polarizers I've seen always have some light loss - but from memory, quite a lot less than acrylic dark enough to make a noticeable difference in ambient light levels.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 04, 2013, 11:44:36 pm
content: Quote from: mc on June 01, 2013, 02:13:45 pmHello, lumens are not enough, it matters also how you manage them: if you trow them all in a narrowangle, or spread them on a wide angle, and also the total emitter surface. More lumens on a small surfaceand lensed into a narrow angle is good to win against sun that is huge and powerfulDisplay brightness (surface luminance) is commonly measured in candela per square meter (nit).For outdoor displays in daylight I remember numbers in the range of 5000cd/m2, but better yousearch for more sources on the net. Usually the displays are seen from a narrow angle, so to obtain veryhigh luminance values, narrow beam leds can be of help, often manufacturers quote directly cd value oftheir emitters, at least at peak angle, this way it's easy to calculate total luminance.Probably Cree Kingbright and others have some documents and appnotes on their sites.

author: Baliszoft
author_rank: Frequent Contributor
timestamp: June 09, 2013, 11:13:24 am
content: Quote from: Baliszoft on June 01, 2013, 05:32:54 pmI meant something like this (i did quite a while ago):

author: mc
author_rank: Regular Contributor
timestamp: June 11, 2013, 11:08:18 pm
content: muvideo, thanks for your post!Balizsoft, thanks for the pics.I spent the weekend at an event with various displays, and I also found some specifications for one of them.For outdoor use, they're all rated upwards of 5000 cd/m2, so I now have a benchmark figure.The basic construction seems to be leds on matt black PCBs, however some use hoods/grids to shelter the LEDs from direct light, whereas as some rely on having everything non-reflective.Now I've got some figures/design ideas, I've at least got a starting point for some experimentation.