Posts Tagged ‘CRI’

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Tungsten vs. Fluorescent vs. LED lights: Light Quality (CRI) and Conclusions (Post #4 of 4)

Monday, March 4th, 2013

This post is the last of a series of four comparing the advantages and disadvantages of different types of continuous lights for photo and video work. Here are the previous ones:

Post #1: Choosing Lights: Tungsten vs. Fluorescent vs. LED
Post #2: Efficiency (i.e., power usage) and Heat Generation
Post #3: Portability and Speed of Setup & Ease of Use

Light Quality (CRI)

When choosing a light source, the final (and perhaps most important) issue is the quality of the light that that light source emits; in other words, its spectrum, or “CRI.” As most people know, light is made up of a whole spectrum of wavelengths, which results in different colors (in terms of visible light, red light is at one end of the visible spectrum with long wavelengths and blue is on the other end, with short wavelengths). Different types of light sources (LED, fluorescent, tungsten incandescent, HMI, the sun) emit different mixtures of wavelengths of light, and the best ones, like the sun, emit a nice, broad, even spectrum of wavelengths (without large spikes or dips at any given wavelength), which allows objects of different colors to appear as vibrant as possible in a photograph or video.

Color Rendering Index (or “CRI”) is a measure of the mix of spectrum that a light emits. This is the biggest advantage of the traditional xenon and tungsten lights: they emit the broadest spectrum of light of any of the types of photo and video lights here (this is because they closely mimic the behavior of a concept known to physicists as “black body radiation.” If physics is your thing or you really want to understand this subject in depth, read about black body radiation and Planck’s law). As a result, tungsten and xenon lights have the highest CRI (100, or close to it). LED and fluorescent lights, on the other hand, emit light that contains more of certain wavelengths and less of others (uneven spikes and dips), and therefore have lower CRIs (from as high as 95+ for good quality lights to as low as 60-70 for low-quality lights). The effect of lower CRIs is that some colors, including skin tones, can appear muted, washed out or unnatural in photos and videos. For this reason it is essential to choose lights with high CRI values.

Both my LED panels and my fluorescent lights have CRI values above 90. That is, they emit a quite broad spectrum of light that will illuminate objects of all colors well (that is not to say that they are accurately color balanced or white balanced for any particular target: CRI and white balance are two completely separate issues… more on that in tomorrow’s post). To illustrate the broad spectrum of light from each of these sources, take a look at the images below.

Emission Spectra ©2013 Chris Conti Photography

The emission spectra of my 1x1 LED panel (left) and fluorescent lights (right). Both show good, broad, consistent output. ©2013 Chris Conti Photography

To make the images above, I projected near-parallel beams of light from my LED (left) and fluorescent (right) light heads into an optical prism, which refracted the light into its constituent wavelengths, and photographed the results. Note that all of the colors of the visible light spectrum are well-represented. This is an indication of the high CRI value of these lights.

 

Conclusions

After experimenting with and testing various lights both in theoretical tests like the emission spectra above as well as practical ones like lighting a white seamless with them, using them for portraits, etc., I’ve made a few conclusions. In no particular order, here goes:

- The concern that LED and fluorescent lights emit poor-quality light as compared to tungsten lights is unfounded. With a tiny bit of adjustment via gels (more on that tomorrow) both from a subjective standpoint (how they look) and a technical standpoint (technical measures of their light emission), these lights look great.

- Both LED and fluorescent lights consume a tiny fraction of the amount of power that tungsten lights do (which makes them more usable in the field), and don’t generate the searing heat of tungstens (which is always inconvenient and can be destructive and painful, and uncomfortable for subjects).

- On the other hand, fluorescents and LEDs don’t generally generate the quantity of light that most tungsten heads do, so it may be necessary to use more of them for certain applications (flooding a white seamless, much less a full cyc wall, requires a huge sheer quantity of light), so these lights might not be terribly well-suited for these applications.

- Fluorescent lights are much less portable and more time-consuming to set up than tungsten lights, but LEDs are easier and faster.

- Light modifiers and accessories like softboxes don’t really exist for LED panels yet (although I did just make a softbox for my 1×1 LED… perhaps that’ll be a future blog post…), but fluorescent heads can usually easily accommodate anything mounted on a standard speed ring.

So what does it all mean? These lights are tools (just like all of our other kinds of gear), and they each have advantages and disadvantages, and are better suited for some tasks and worse for others, and the right tool for the job will depend on the particular job: lighting a large stage with a two-wall cyc wall is still best done with high-power, high-output tungsten or HMI lights. A quick location interview is probably best done with a couple of LED panels. For a small- to medium-sized studio shoot, fluorescents are probably the best bet.

Tomorrow I’m going to be going to a location and shooting in the same room all day. What will I bring? Fluorescents and a couple of LEDs.

I’ve learned a lot experimenting with all these different types of lights. If you’ve read this blog post and the few that came before it, hopefully I was able to share some of that with you. If you have any comments, different opinions or questions, let me know!

-Chris

P.S.- Since I’m going to be using a mixed bag of different light sources that result in a mixed bag of  color temperatures, in order to work well together the lights need to be balanced to each other. Balancing my mixed bag of lights will be the subject of tomorrow’s post…

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Tungsten vs. Fluorescent vs. LED lights: Portability and Ease of Use (Post #3 of 4)

Thursday, February 28th, 2013

This post is third in a series comparing the various types of continuous lights for photo and video work (it’ll definitely make more sense if you read the previous ones).

Post #1: Choosing Lights: Tungsten vs. Fluorescent vs. LED

Post #2: Efficiency (i.e., power usage) and Heat Generation

Portability

This is also something that is less important for photographers and videographers who work primarily in a studio, but for someone like me whose work is almost entirely on location, it is important. Tungsten and HMI light heads are usually relatively compact, but they are fragile; the bulbs are made of very thin glass and even thinner filaments, and can break if jostled around too much (especially if they’re cold, as tends to happen here in the northeast in winter). Also, since tungsten and HMI lights get so hot when they’re in use, at the end of a shoot they need to have a fair amount of time to cool down before being packed away or they’ll melt case fabric or padding or cables, gels or whatever else they happen to come in contact with in the bag or case… and a melted plastic power cable just sucks.

Fluorescent light heads have got to be the worst when it comes to portability. Since they don’t get hot you don’t have the issue above, but instead the bulbs are larger, bulkier, and even more fragile. My 3-head fluorescent kit is HUGE, because the bulbs are so fragile they need to be transported in individual cases (and with five bulbs per head, that means I’m carrying around 15 bulb boxes in the kit).

Definitely better in the studio: moving fluorescent fixtures is a huge pain.

Definitely better in the studio: moving fluorescent fixtures is a huge pain.

I can drive my fluorescent kit to a location, but don’t even think about flying with it… the kit is bigger than airlines’ maximum allowable suitcase size, and even if you could get it on the plane, by the time you picked it up at baggage claim all the bulbs would be shattered anyway.

And then there are LEDs… oh, blessed LEDs. LEDs are tiny, compact, rugged and oh-so-easy to travel with. Since they have no bulbs and no glass, LED panels are by far the most durable and least fragile of the lights here. Advantage, LEDs.

Speed of Setup and Ease of Use

Speed of setup is another issue that studio dwellers probably aren’t terribly concerned with, since lights that live in a studio frequently can stay set up and don’t need to be broken down between shoots. But for those of us always on the go it is a consideration. And here once again, fluorescent heads are the clear loser. Setup of tungsten and HMI heads is pretty straightforward: you put the head on a stand, plug it in, attach whatever modifiers you want to use, and you’re good to go. Takes a couple of minutes per light, tops. With fluorescent heads though, it’s a different story. In addition to all of the same steps you’d take with a tungsten head, with fluorescent lights each individual bulb (of which there can be anywhere from three to six per head, depending on the model) has to be carefully removed from its case and carefully installed into the head before any modifiers are attached, drastically increasing the setup time. LED panels, on the other hand, couldn’t be simpler to set up. You stick the panel on a stand and plug it in. Done. One of these lights can literally be set up in under 30 seconds. Advantage, LEDs.

Usability is a much more complex question (and a really important one). Here, tungsten and HMI lights really benefit from having been around for far longer than LEDs and fluorescents. The design of tungsten and HMI heads have been refined over years, and a whole universe of accessory modifiers have been developed to work with them: Fresnel heads use a lens and a moving focusing mechanism to allow light from these heads to be tightly focused into a spot or allowed to spread more flood effect. All manner of modifiers (umbrellas, snoots, gobos, softboxes of every conceivable shape and size, etc.) have been designed for these lights, and as a result they are extremely versatile. Fluorescent and LED lights, however, unfortunately are still new enough that for the most part these accessory modifiers are not yet available for them. Additionally, the design of most of these lights prevents them from benefiting from Fresnel-type housings, so their beam tends to be very wide (although a couple of companies are just starting to make LED Fresnels… take a look at these Arris). As a result, the light from panel-type LEDs and most fluorescent heads disperses quickly, so these lights tend to have short “throw” distances. Coupled with the lack of modifiers, this limits the versatility of LED and fluorescent lights. I am certain that modifier manufacturers will quickly start designing softboxes and other accessories for them, but for the time being, this leaves fluorescent and LED lights at a disadvantage.

Tomorrow’s post, the last in this little series, will look at quality of light emitted by the various types of light (the CRI), and my conclusions.

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Choosing Lights: Tungsten vs. Fluorescent vs. LED (Post #1 of 4)

Tuesday, February 26th, 2013

(Note: I originally started writing this as a single post, but it turns out there is so much to say on the topic that I’m going to break it into several posts. Links to the others will be at the bottom.)

I recently found myself in the same situation that every photographer and videographer occasionally faces. I’m currently expanding my arsenal of photo and video lights, so I’ve had to tackle the question of which type of lights to buy. Since my work includes both still and video (and since I already have a selection of strobe lights that I’m happy with), I’m focusing now on continuous lights that can be used for either still or motion work.

First, some background. As photographers and videographers know, the most commonly used lights have traditionally been xenon gas flash tubes for still photography and tungsten incandescent bulbs for video and film (HMIs are also somewhat common for motion as well, but less so than tungsten). These traditional kinds of lights work very well and they definitely still have value in the right application (in fact, in certain types of applications they’re still the best type of light there is), but they do have significant weaknesses and disadvantages, and recent technological advances have improved other light sources such as LEDs and compact fluorescent bulbs to the point where they too are now practical for photo and video use.

Choices choices choices!!!

Choices choices choices!!!

So we now have this whole range of light sources available to us that includes the traditional tungsten and HMI (such as those made by Arri, Mole-Richardson and many others), fluorescent (in both tube format like Kino-Flos and CFL format like Westcott Spiderlites) and LED (like Litepanels) as well as some even newer and more exotic technologies that are still coming to market like organic and plasma panels (the Zacuto “PlaZma light” will be very interesting to keep an eye on once it is introduced, hopefully later this year).

Among all of these options, how do we choose the right light? Every type has advantages and disadvantages, and as with most things, which is best comes down to your individual needs and what type of work you do. Personally, the vast majority of my work is done on location instead of in a studio, so the factors that are important to me are 1) efficiency (i.e., power use), 2) heat generation, 3) portability, 4) speed of setup and ease of use, and most importantly, 5) light quality (CRI). (Cost is of course also a factor, but with each type light there are expensive options and cheaper options, so that’s less relevant). So for my current round of equipment purchases, I evaluated each of the light types on each of the criteria above. In the next couple of posts I’ll talk about how the various types of lights compare when it comes to efficiency, heat generation, portability, speed of setup and ease of use, and light quality, finally ending with my conclusions and my purchases.

Tomorrow I’ll talk about the efficiency and heat generation of each types of light heads.

(Update: Links to the subsequent posts in this series are here:
Post #2: Efficiency (i.e., power usage) and Heat Generation
Post #3: Portability and Speed of Setup & Ease of Use

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