The fact that you are reading this shows that you have wondered about projecting during the day. This question is relevant whether you want to use daytime projection for work or entertainment.
In this blog post, I will show you what can be done to make the light emitted by an electronic (such as a projector) to be perceived as being brighter than the sun. So, it’s not just about getting a projector enclosure and projecting.
That means that before anything else, we need have a way to measure brightness. This way, we will know how much light we need to overshadow the sun.
Let’s get started!
How To Measure Brightness
You’ll be happy to know that there are a number of units to measure brightness. Let us look at a few examples.
The lumen is a measure of how much light (quantity) a source emits. What makes the lumen special is that it takes into consideration that some light sources send light in different angles (like your lightbulb).
The candela measures the intensity of light that a source emits in a single direction.
Lux measures the number of lumens when a light source is applied to a surface area. So you can have a light source that has 10 lumens per square meter, and another with 2 lumens per square meter.
Regardless of the lux of a light source, the general rule is that the light will get dimmer if applied to a large area.
A foot-candle is similar to a lux. The only difference is that while in lux we use the metric system, the foot-candle uses the imperial scale. You are probably wondering how these measurements relate to each other. I’ll save you the trouble:
1 foot-candle is equal to 1 lumen/square foot, which is equal to 10 lux.
Similar to lumens, nits measure the quantity of light from a light source. The main difference is that nits measure the brightness of devices with screens. Examples are phone screens, computer monitors, and televisions. With such devices, there isn’t one point of light, but rather a field of light.
Now that we have the various ways of measuring light under our belt, let’s have a look at the brightness of various everyday objects.
The Brightness of Everyday Objects
Direct sunlight: Ranges from 32,000 lux to 100,000 lux
Sunlight on an overcast day: 1,000 lux
Light from domestic light bulbs: 50 lux to 250 lux
LIght from a full moon on a clear night: 0.36 lux
Light from stars: 0.0001 lux
The next question is, how were these measurements achieved? One of the tools is called an illuminometer, which is no stranger to people who work in photography. Other areas that use illuminometers are horticulture and museums for controlling light.
Now, to the cool stuff! Let us think about light from projectors and how this compares to the sun’s light.
Measuring the Light Emitted by a Projector
In our calculations (yes, there is some math), we’ll make some assumptions and leave out other factors to make things a little easier.
The first assumption is that most projectors are designed to project in an aspect ratio of 16:9. Now lumens per square meter has a 1:1 ratio, which will make the conversion to a 16:9 ratio a nightmare. So let us assume that the projector will emit light on a square area rather than a rectangular area.
But here’s the deal:
There is no universally-accepted standard for what makes up a lumen. So, let’s assume that we are referring to the color range between pure white and black. Remember that we all perceive colors differently.
We should also remember that most projectors cannot emit a pure black color. They also cannot show all the colors from 0 lux to pure white. In other words, measuring brightness accurately is very hard, thus, we simplify.
Light Emitted by Indoor Projectors
If our projector emits 1,000 lumens on an area of one square meter, with colors ranging from 0 lux black to 1,000 lux white, we will have an adequate contrast ratio to display all the colors in a dark room.
As we previously saw, indoor light produces around 250 lux. This means that black will start at 250 lux, but white will remain at 1,000 lux. By starting black at 250 lux, we have reduced the color contrast and our videos and images are a bit unclear.
Now check this out:
If we open the windows in the room and allow outside light to come in, the brightness level increases to 1,000 lux. This means that our brightest white is the same as the light hitting the wall. We have no black, and so our images and videos are not visible at all.
Light Emitted by Projectors in the Shade
Before anything else, let’s be clear that to operate a projector outside, it’s a good idea to get a projector enclosure to protect it from damage.
The daylight brightness in a shade is around 10,000 lux. So if we want the projector to show videos and images with a 1,000 lux contrast, we need our projector to emit a minimum of 10,000 and the white should be 11,000 lux per square meter.
The problem is that we would find it difficult to notice the contrast because of the numerous chemical changes that take place within our eyes. In a dark room, the 10,000-lumen projector will have more contrast than the 1,000-lumen projector. However, our eyes would find it hard to tell the difference. Also, 10,000 lux white images will be unbearable for our eyes.
Light Emitted by Projectors in Full Daylight
On a full sunny day, the sun’s brightness is at 100,000 lux. So as to achieve this kind of brightness, we would need a projector that produces 100,000 lumens at the very least.
I’m not going to lie to you…
Such projectors just don’t exist. The world’s brightest projector emits 43,000 lumens and uses 7kW of power. Now, a 20,000-lumen projector uses 3kW of power and looks like this:
Speaking of which, all projectors heat up to temperatures of 200 – 300 degrees. We have amazing tips on how to control the heat from your projector.
Back to business:
You might be wondering, can’t I just join 3 or more such projectors to get the desired brightness? The thing is that with additive light, the black light will be raised much higher.
Remember when we said that the smaller the surface area, the brighter the light? Well, a 20,000-lumen projector can produce 100,000 lux brightness on a surface area of 0.20 square meters. Too small for a theater, right?
Also, the optics in the projector consume significant amounts of brightness to generate clear images and videos, and this will call for more brightness. Above all, you’ll be using a lot of electric power on your projectors.
Is There a Solution?
There are things that you can apply on the projection surface to reduce the amount of sunlight it absorbs and reflects. For example, you can use a silver screen that is better at reflecting light from the front than light from an angle (like the sun from above).
You could also go with grey screens which absorb less light than white screens. Grey screens are especially handy when combined with rear projection. You’d, however, need to add as much shade on the front as possible.
As we have seen, it’s unlikely that we’ll be able to use projectors in full daylight. However, there are other ways of showing information clearly even on bright days. If you visit Times Square, you’ll see LED video walls. These are just many LEDs bundled up.
While, projection surfaces are designed to reflect full spectrum light, LED panels are black and designed to block ambient light. LEDs produce their own bright lights and so already have the required contrast to produce clear images.
The brightness from LED walls is measured in nits rather than lumens. Nits measure the emissions from the surface area rather than the reflections. One nit is equal to 3.426 lumens.
And that’s where we (the experts) come in…
Ssidisplays.com has manufactured premium-quality projection surfaces and displays since 2005. Our digital display solutions are targeted at retailers, manufacturers, institutions, governments, the military, and private individuals. Get in touch with us today and learn how we can meet your needs.