How to do video projection in full daylight

Your Enemy.

TL;DR — You can’t. This is a serious clickbait title.

I’ve been in audio visual stuff for a while and still get requests or questions about doing outdoor projection during the day. Unfortunately, until we invent some super charged light cannon or an anti-light shadow beamer, this is not happening anytime soon.

This writeup will deal more with the hypothetical of “What it would take for an electronic light to be perceived as brighter than the sun?” This is a good time to note that I’m not a scientist — this is just a fun thought experiment. Fair warning that there will likely be more than one inaccurate statement or concept that follows.

First, we need to answer “How is brightness measured?” — then we’ll get into the hypotheticals of how much brightness we would need to compete with the sun.

There are many different methods of measuring light, and some of the relevant ones for this thought experiment are as follows:

  • Candela — intensity of light emitted by a source in one particular direction.
  • Lumen — quantity or flux of light emitted by a source. This takes into the account that most lights (like a candle) are essentially omnidirectional and shoot light out at lot of different angles
  • Lux — a measurement of lumens when applied to a surface area or 1 lumen/sq. meter. Light gets dimmer as it is spread out over a larger area
  • Foot-candle — related to lux, but uses the imperial system of measurement instead. 1 foot-candle = 1 lumen/sq ft. = ~10lux
  • Nits — similar to lumens, but used more as a brightness measurement for display devices like smartphone screens and monitors where there isn’t a single point of light, but rather a field of light.

Example lux readings from wikipedia:

  • Moonlight Night/Starlight — 0.0001 lux
  • Full Moon, Clear Night — 0.36lux
  • Home lighting — 50–250lux
  • Overcast Day — 1000lux
  • Direct Sunlight — 32,000–100,000lux

To actually obtain these measurements, there are several tools available. I used an Illuminometer to see these for myself. These light meters are mostly used in the photography industry, but they are useful in a lot of other areas as well, from horticulture, to museum lighting and others.

With my illuminometer, I was able to get a reading of anywhere between 90,000 and 110,000 lux on a bright sunny day in NYC in June. Moving into the shade of a tree and getting indirect light was usually anywhere between 3,000–9,000lux.

With these readings in hand, we can start thinking about how bright a projector typically is over a given surface area.

Simplified Assumptions

To get a few things out of the way first, there are several known things we’ll just make assumptions about, or leave out of our calculations. First, Projectors are typically made to project in a 16:9 aspect ratio which is going to make our calculation for lumens per square (1:1) meter a little more challenging, so since this is a hypothetical exercise anyway — we can just assume projectors are going to cover a square and not a rectangle. Secondly, projector manufacturers have pretty different standards on what constitutes a lumen (some follow a standardized ANSI lumen measurement). We can also assume we’re talking about black to pure white here as different colors have different perceptual brightnesses to our eyes. Full color images will potentially need even more light to appear vivid than just black and white gradients. Finally, most projectors can’t project a pure black and don't actually go from 0 lux to full white in a pitch black room. (btw Medium renders a zero and lower case O the same…weird…o0o0o0o0). In short — measuring brightness is complicated and we’re drastically simplifying.

Indoors

Alright — with that out of the way. If we have a 1,000 lumen video projector covering a square meter of surface area (not a very big surface), lets say our black level is 0 lux and our brightest white is 1000 lux. This gives us a good contrast ratio to show all the colors between black and white in a dark room. Now, lets turn the lights on in this room and pretend we just bumped up the ambient lighting in the room to 250lux. Now our black level on our surface area is starting at 250lux and our white is still at 1000 lux — our contrast has gone down and the image is starting to look pretty washed out. Let’s open the window in the room and raise the brightness to 1000 lux. Now the wall surface is as bright as our projector can go and there really is no space for a black level — our projected image, even if its pure white snow — probably isn’t visible at all at this point.

Contrast matters

Outside in the shade

Let’s go outside into the shade where it’s 10,000 lux of brightness today. This means to get even our previous contrast of 0–1000lux, we’d have to start with a 11,000 lumen projector projecting a square meter. Our black is the 10,000 lux surface and our white is the brightest spot of our 11,000 lux projection. Perceptually, to our eyes, this sense of contrast gets a little difficult to explain because of all the optical and chemical changes going on for our eyes to adjust and perceive these different brightness levels. A 10,000 lm projector in a dark room on a 1m square surface may have a better contrast ratio than a 1,000 lm projector on the same surface area, but your eyes might have a hard time telling the difference. Or the whites of a 10,000 lux image that small might be painful or unpleasant to look at.

Full Daylight

If you’re still following — let’s move up to full daylight. We’ve got a square meter projection screen in the desert and it’s a full sunny day at 100,000 lux coming from our screen surface just from the sun. To even reach this kind of brightness on a single square meter with a projector we would need a 100,000 lumen projector.

Unfortunately — these don’t exist. 😨

The world record for brightest projector is sitting at 43,000 lumens. It consumes 7kW of power. A much more standard 20,000 lumen projector consumes around 3kw and looks like this:

Barco FLM20 sitting on a roadcase

“Well — can’t you just stack 2 or 3 of them and add them together?” Unfortunately additive light doesn’t work that way. Just because there are double the lumens coming from these projectors doesn’t mean it is perceptually twice as bright. This is because of something I mentioned earlier where projectors typically don’t project zero lux as black, especially the brighter ones. So stacking 2 projectors and projecting black will raise that black brightness even more, hurting your contrast. Stacking 2x 5,000lm projectors gets you something like 7,500lm, not 10,000.

We could get 100,000 lux of brightness with a standard 20,000 lumen projector, but only on a very small surface area — only 0.20 square meters or 20 x 20cm. Not exactly a movie theater sized screen.

What if we want to cover a normal sized theater screen with projection in full 100,000lux daylight. Lets say a 10m x 10m projection surface or ~33ft x 33ft. To even match 100,000 lux on a screen that size, we would need a single projector capable of projecting 1 million lumens of brightness. We’d need to add another 50–100% to that just to give us an appropriate contrast of black to white. So with our pretty standard 20,000 lumen projectors we are only at about 1–2% of the brightness we would need to cover an appropriate screen. Even if we go back to our approximate 16:9 aspect ratio for a real screen, that only cuts down our surface area to a little more than half of a 10m x 10m surface and brings us into the 500,000–750,000 lumen range. A 20,000 lumen projector is typically plenty bright in a normal movie theater where a 30ft wide screen might be getting around 400lux for its surface.

As far as power consumption and heat — We’ll just (inaccurately) follow a linear increase for lumens and wattage (20k lumens was about 3500W, 43k lumens was about 7000W) — this means to power our 1 million lumen projector, we would need about 175000W of power. All dependent on the type of materials used to generate that light — like LED’s using less power than incandescent — although most projectors in the bright end use xenon bulbs. I’m not sure of the proper way to calculate potential heat dissipation for something that bright, but it’s probably bright and hot enough to melt most materials that can even generate, contain and direct that much light in a small surface area.

There are videos out there of super bright flashlights that do get into crazy amounts of lumens (here is one claiming 90,000 lumens), but projectors have to pass through a lot more optics just to actually generate their image and this costs significant brightness. Removing the color wheel from a DLP projector can double or triple the brightness for example.

There are things that can be done to improve the surface itself for projection so that it doesn’t absorb as much sunlight. Some of these screens are things like silver screens that reflect light coming from front on much better than light coming from above. Gray screens can help a bit as they reduce the absorption of ambient light — especially if combined with rear projection and as much shade as possible over the front.

What about LED walls?

Brooklyn’s Barclay’s Center and their massive wraparound outdoor LED wall in full daylight

So…projection outside in full daylight — probably not possible anytime soon. But what about LED video walls? Those are visible in Times Square during any point of the day in full light and they are just a bunch of tiny LEDs. However, a projection surface is designed to reflect full spectrum light — which reflects the projector and all this ambient light. LED panels don’t have this problem — they are black and designed to absorb ambient light and emit their own bright light. This means the contrast needed to perceive a nice image doesn’t need to be anywhere near the level of projection.

As discussed earlier, things like LED walls are measured with nits instead of lumens.

Nits are more about emission from a surface area instead of just reflecting other light. The conversion (that people much smarter than me have figured out) is:

1 Nit = 3.426 Lumens

An iPhone screen is about 600–700nits at maximum brightness. Outdoor LED tiles are incredibly bright per square foot — these Barco tiles are 5,000nits — or an equivalent 17,000 lumens per square foot tile. 5000+ nits are recommended for outdoor direct sunlight applications. But this isn’t even getting to the brightness of the actual LED die itself — the tiny point of the LED that actually emits the light. The LED die might be somewhere closer to 100,000 nits over its tiny surface area. So to our eye, that looks much brighter than the rest of the black LED panel. If you break down the surface area of an LED panel, maybe only 4% is the actual points of light and 96% is just blackness devoted to absorbing sunlight. This makes the perceived brightness be a lot higher than just projected and reflected sunlight.

Wrap up

You can’t project a light sucking black anti-photons and you can’t project and compete with the sun — stick with LED walls if you’re outside.

There are also specialized LCD monitors made specifically for the purpose of outdoor usage — they also come with the bonus of being weatherproof and are a better choice for a wide range of temperatures and environments.

References other reading:

Measured versus perceived light

Nits versus Lumens

Nits versus Lumens — proAV

Nits versus lux

Candela, Lumens, Lux: The Equations

Understanding and interpreting lux values

Flashlights claimed to be brighter than the sun

Lumens and lux explained in an image

XKCD: What if everyone on earth pointed a laser pointer at the moon, would it change color?

Sunrise photo taken from: https://astrosolar.com/en/gallery/images-various/sebastian-voltmer-sunrise-spicheren/