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What's wrong with my LEDs, where should I look to solve?

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#1 Macks Fiiod

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Posted 13 January 2016 - 11:38 PM

 

Hey this is my first post here so let me know if I'm screwing up out the gate.

 

I've been shooting shorts with a DSLR and some cine lenses for about 3 years now. For 2 of those years, I've had a pair of LED lights made by Bescor in my arsenal, here's a link to them for the stats/info:

http://www.bhphotovi..._LED_Light.html

 

Obviously, I don't know my way around lamp statistics, applications, etc. and wanted to post what I don't like about these and hopefully get some advice from you guys on what specifically needs to be better. The 2 main gripes I have with these LED lights are a lack of brightness, and an odd shadow casting that appears jagged, similar to the shadow in this picture

astra_Jagged_Shadows.jpg

 

Every time people ask stuff like this the first reply seems to be "well what do you want to do?" and my answer for that would be either run and gun documentary/videography OR a slower workflow for something like an indoor short film shoot.

 

If you guys have any easy guides to LED light stats, lists of brands to love/avoid, or any specific recommendations for under $1000, it'd be much appreciated.

 

Thanks in advance for replies.


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#2 Stuart Brereton

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Posted 13 January 2016 - 11:57 PM

I can't comment on the lack of brightness, but the 'odd shadows' are caused by the fact that the lamp has multiple LED sources rather than single source like a halogen lamp. That's entirely normal for an LED lamp of that type. If you want hard shadows you should look into buying some tungsten fixtures.


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#3 Macks Fiiod

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Posted 14 January 2016 - 01:06 AM

I can't comment on the lack of brightness, but the 'odd shadows' are caused by the fact that the lamp has multiple LED sources rather than single source like a halogen lamp. That's entirely normal for an LED lamp of that type. If you want hard shadows you should look into buying some tungsten fixtures.

Thanks for the info on the second point. Have any Tungsten recommendations?


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#4 Satsuki Murashige

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Posted 14 January 2016 - 02:17 AM

The best panel LEDs of the style you are using now would probably be the Litepanel Astras. They are quite bright. As Stuart says, the multiple shadows are typical of this sort of light so some of the better ones have diffusion panels to blend the many little LEDs into a single large source. You can do the same by purchasing gel sheets and cutting them to fit your light. I would recommend starting with Lee 216 which is a heavy full white diffusion: http://www.filmtools...1-lee-s216.html

You can also bounce the LED off of a white card or even a white wall to soften the light. Both bouncing and diffusing will cause a loss of intensity, so these methods are done better by starting with larger, brighter sources like tungsten lamps. There are all sorts, but the basic ones are open-face lights, pars, fresnels, and ellipsoidals.

Open face lights are the most simple and thus the cheapest. Basically, there is a large wattage bulb or globe in a metal housing with a silver reflector to concentrate the light out the front. It has a yoke with a mount for a baby stand, barn doors, and a knob that moves the globe forward or back inside the housing - that's it. It usually comes in 1k (1000w) or 2k (2000w) varieties. You can use it to bounce light off a ceiling, to push it through heavy diffusion, or as a backlight. The shadow quality is unrefined, so you wouldn't typically use it as a key light directly. Think of it like a big dumb brute - cheap, nasty, and powerful.

The par light is similar but it has a parabolic reflector (thus par) that concentrates the light a bit more. In addition, it typically has a diffusing glass on the front. Often, the globe comes fully sealed with the reflector and diffusion glass on the front - these are the same types of globes used in car headlights. You can choose how much the light focuses or spreads by choosing the type of diffusion. Clear glass has the narrowest beam and the most punch, stipple has the most spread. The par is still best used for applications that need lots of punch like lighting background buildings on night exteriors but since they can be controlled a bit more they also get used for rough spot lights, hard sunbeams through windows, etc. You can get dirt cheap 1k parcans that put out a massive amount of light. The large stadium lights or aircraft landing lights that are used to illuminate a huge area from a distance are ganged groups of pars. In film, we call them Nine Lights, Wendy lights, Jumbo lights, and Maxi-Brutes. They require a massive amount of power and generate an enormous amount of heat, but they are extremely bright.

The fresnel is the workhorse light. It is an open face that has a focusing lens on the front which collimates the beam of light to create relatively parallel light rays, giving sharp shadows. If you look at movies from the 30's to the late 70's, this was the standard key light. Sometimes diffused or bounced, but often used directly. They come in sizes from 20k all the way down to 150w. Most studios will have 10ks, 5ks, and 2ks lying about, the typical field kit would have 2x 300w, 2x 650w, and maybe a 1k. The small ones are often used as accent lights, the big ones to simulate sunlight or to illuminate massive sets.

The ellipsoidal is a projection light often used in theater as a spotlight. It has complex optics that project a sharp circular beam. The lenses can be swapped out to project different sized beams, and there are metal shutters inside to cut the light sharply. They are often used in conjunction with colored gels for effects. More recently, cinematographers have used them to simulate sharp sunbeams, or as bounce lights that can be sharply cut to any desired shape close to the actors without requiring flags.

One manufacturer, Dedolight, makes a light that is a kind of hybrid between a fresnel and an ellipsoidal. It uses dual lenses to create a sharper, more efficent beam than a fresnel and can be flooded wider and spotted tighter. It can also use a special lens attachment to turn the lamp into a projected light just like a soidal. They are more expensive than fresnels, but they are worth it. Their 150w Dedo can be almost as bright as a 1k fresnel, though with a fraction of the spread. This would be my suggestion if you are looking to start building a tungsten kit.

There are still further types of tungsten units, but this covers the basic ones. Most of these types of units (pars, fresnels, ellipsoidals, Dedos) are also available as HMIs, which are much brighter per watt and naturally daylight balanced. However, HMIs require a special ballast to operate and are therefore many times more expensive than their tungsten counterparts.
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#5 Satsuki Murashige

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Posted 14 January 2016 - 04:07 AM

Forgot to mention that fresnels also have a small reflector that travels with the globe towards or away from the fresnel lens as you flood or spot the light. This helps the efficiency of the light by directing it all back into the lens.
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#6 Macks Fiiod

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Posted 14 January 2016 - 01:21 PM

 

Thanks for the tips. What do you guys think of something lower on the totem pole, like something by Genaray for $200-$400?

http://www.bhphotovi..._75w_AC_DC.html


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#7 Satsuki Murashige

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Posted 14 January 2016 - 02:51 PM

Well, just by looking at the design it appears you're going to have the same problems with multiple shadows...
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#8 Stuart Brereton

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Posted 14 January 2016 - 02:55 PM

That's another multiple LED source, so you'll have the same multiple shadows that you dislike. The output seems pretty good, roughly equivalent to a 500w tungsten lamp.


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#9 Satsuki Murashige

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Posted 14 January 2016 - 02:58 PM

But the color on the other hand... Test and see, I guess. Personally, I'll stick with a $20 paper lantern.
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#10 Macks Fiiod

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Posted 14 January 2016 - 04:30 PM

 

I've come to accept the multi-shadow deal. Just thought it was only happening because my kit was cheap. If that's just the nature of LED I'll live with it, also thanks for the tip on that product.


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#11 Satsuki Murashige

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Posted 14 January 2016 - 08:56 PM

It's not the nature of LED units so much as the design of the panel. As I mentioned before, there are more expensive LEDs as well as Remote Phosphors that have built-in diffusion panels. There are also LED fresnels like the Dedos and Arri L7 series, but those tend to be more expensive.
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#12 Robin R Probyn

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Posted 15 January 2016 - 05:47 AM

Any light with multiple sources like that on a panel design,without diffusion .. will give multiple shadows.. if there were 10 suns you would get 10 shadows on a sunny day.. LED,s to Dino,s.. the same.. 

 

Pricey .. but the Arri Locaster has some clever tiny plastic bubble type diffusion in front of the LED panel .. that truly gives one source and even has barn doors to prove it !..  


Edited by Robin R Probyn, 15 January 2016 - 05:51 AM.

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#13 Adrian Sierkowski

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Posted 15 January 2016 - 09:26 AM

If the multi-shadows really annoy you, you can get away with a light diffusion to help mitigate the problem. Often I throw a little bit of Opal on LED panels. Of course, with anything in front of them, you loose output on the unit itself.


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#14 Guy Holt

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Posted 16 January 2016 - 10:09 AM

If the multi-shadows really annoy you, you can get away with a light diffusion to help mitigate the problem. Often I throw a little bit of Opal on LED panels. Of course, with anything in front of them, you loose output on the unit itself.

 

Given that the OP is already complaining about insufficient output,  I don’t think this is a solution.  It seems like what he wants is a Fresnel light.  Unfortunately that is hard to accomplish with LEDs because Fresnel lenses require a point source of light and to date there is no single emitter LED capable of replicating a tungsten filament or short arc HMI in that regard.  Though probably the oldest type of light, Fresnels are by far the most versatile. What makes them so versatile is their incredible optics.

 

A Fresnel lens can be regarded as an array of prisms arranged in a circular fashion, with steeper prisms on the edges and a nearly flat convex lens at the center. The prisms near the center of the light source act as "dioptric" lenses that magnify and concentrate the output of the lamp filament. At the same time, the multiple prisms mounted around the periphery of the lens (above, below, on one side and the other of the filament), act as "catadioptric" lenses that collect and intensify the light and redirect it in the same plane as the dioptric lenses towards the center. In this fashion, a Fresnel lens bends the light of a source into a column of nearly parallel rays as shown in the illustration below.

 

fresnel_lens.jpg

 

A common misunderstanding is that the reflector collimates the light of a Fresnel head. In fact, the purpose of the reflector is to double the intensity of its' output. When the light-emitting filament of the bulb is placed near the center of curvature of a spherical, concave polished mirror reflector, the reflecting surface creates an image of the filament. That image is located in the same plane, but slightly displaced from the filament itself. This has the effect of doubling the amount of light forward projected from the locale of the lamp filament

 

Fresnel_Doubling.jpg

 

In other words, without the reflector, "this reflector light" (the dashed lines in the illustration above) would have been lost in the back of the lamp housing. With a reflector, these rays of light are collected and sent back to their point of origin where they emanate forward, parallel with the direct rays of light from the filament (the solid line in the illustration above), towards the back of the Fresnel lens where they are together collimated by the lens (for this reason the filaments of the bulbs used in Fresnel heads are designed with an open geometry to minimize blocking of the retro-reflected light - making them not quite an ideal point source.)

 

 

Fresnel_Pattern.jpg

 

Now that all the light that emanated forward and back, emanates forward from a single point within the fixture (the filament and its mirror image), the light projected forward is doubled. The efficiency of this lamp/reflector design, the collimated quality of it's light output, and the ability of the Fresnel lens to focus the rays of light quickly and easily to obtain a desired intensity or beam width, is what makes the Fresnel head one of the most versatile fixtures to work with.

Without the doubling effect of a mirrored reflector, more output is required from a single emitter LED to generate a light output comparable to a tungsten or HMI Fresnel.  The Quantum Dot technology being developed by Mole Richardson holds some promise but still is not capable of the output of a tungsten filament. There is a lot more to not like about LEDs: the color rendering capability of most LED lights is pretty poor and their power supplies can draw harmonic currents making them a poor choice  to operate on portable generators. Use this link for more details about the drawbacks of LEDs and a very informative video demonstrating that the color rendering problems are not easily remedied in post.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Sales and Rentals in Boston


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#15 Phil Rhodes

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Posted 16 January 2016 - 11:42 AM

A common misunderstanding is that the reflector collimates the light of a Fresnel head. In fact, the purpose of the reflector is to double the intensity of its' output.

 

If you want to talk about efficiency, let's at least mention PARs. Fresnels are actually horrifyingly inefficient compared to a PAR, especially when the reflector-lampholder assembly is near the back of the light, when it's adjusted to produce narrower beam angles. A lot - often the majority - of the light just gets fired into the walls of the lamphouse.

 

Useful, flexible, absolutely. Efficient, not so much.

 

Apropos of power factor, d'you happen to know what Mole have done with the Senior LED? At 900W, one would have hoped they'd have power factor corrected it.

 

P


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#16 Guy Holt

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Posted 16 January 2016 - 03:03 PM

 

If you want to talk about efficiency, let's at least mention PARs. Fresnels are actually horrifyingly inefficient compared to a PAR, especially when the reflector-lampholder assembly is near the back of the light, when it's adjusted to produce narrower beam angles. A lot - often the majority - of the light just gets fired into the walls of the lamphouse.

 

Useful, flexible, absolutely. Efficient, not so much.

 

Apropos of power factor, d'you happen to know what Mole have done with the Senior LED? At 900W, one would have hoped they'd have power factor corrected it.

 

P

 

But pars won't give you clean crisp shadows unless they are far far away.

 

I have only had the opportunity to test the smaller 150W Mole LED Fresnel, but if it is any indicator the 900W is probably power factor corrected. As you can see by the power quality meter readings below, the Mole 150W LED has a power factor of unity and draws virtually no harmonic currents.

 

Mole150_PQ_Comp_Sm.jpg

(The 150W Mole LED has a pf of unity and Total Harmonic Distortion of 4.6%)

 

This is in stark contrast to Litepanel’s Sola4 LED Fresnel (below) that has a power factor of .60 and total harmonic distortion of 77.7%. In conducting tests of LED lights, I am discovering that a lot of LED AC power supplies are not power factor corrected (pfc) making them much less efficient than tungsten lights that have unity power. With power factors as low as .45, LEDs can draw twice the current than a tungsten light of the same wattage. If you don’t take into account the extra current they will draw and the harmonic currents they will generate, you may find breakers tripping and portable generators running erratically.

 

Litepanel_Sola_4_Composite_Sm.jpg

(The Litepanel Sola 4 has a pf of .60 and Total Harmonic Distortion of 77.7%)

 

The manufacturers of LED Light fixtures generally do not give power factor specifications for their products. One would think that the less expensive LED lights would not be pfc, while the more expensive ones would, but that proved not to be the case in recent testing I did of fixtures. Over half of the fixtures that I tested at random (from the inventories of Boston area rental and lighting sales companies) were not pfc. With power factors ranging from .45 to .63, these fixtures generated considerable harmonic distortion (THD ranged from 75-85%.)

 

Astra_Composite_Sm.jpg

(The pf of the Litepanel Astra drops to .54 when dimmed to 50%)

 

Even those that were pfc generated harmonic currents when dimmed. For instance, the pfc of the new Litepanel Astra 1x1 above dropped from .99 to .54 when dimmed 50% (THD increased to 83.2%.) To see which LED lights are power factor corrected or not, use this link - http://www.screenlig... Output AC LEDs - to see some of the results of my tests.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston


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