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delbz

Bias Lighting

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I just use one table lamp on one side left of screen and a pedestal lamp on the right of the room (both behind the plasma screen & both rated at 25w) works well for me.

I wouldn't use flouro's mainly because they change light spectrum/colours in the room also have bad experiences of rf interference from them in my system.

I see the new range of philips lcd/plasma come with a built in backlight.

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All,

Incandescent lamps are the wrong colour white. They should match the TV white which is daylight (D6500 K) You can buy daylight fluros. They usually need to be reduced in brightness to 30 % of the lightest white in the display. This can be done with a grey filter material. This will increase the contrast provided the light does not hit the screen.

LCDs have a D6500 K fluro and a dispereser behind the LCD.

AlanH

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Hi all,

The top of the range "Metz" televisions come with a rear light already fitted.

They have done so for a few years now.

They are one of the best tv's in the market, expensive though.

Cheers

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I eventually bought a Crompton Slimline Linkable Fluorescent 20watt light (for about $45 from Bunnings) and positioned it behind the centre speaker.

http://cromptonlighting.com/fittings/index...base_database=1

Wow - this looks good - showroom stuff. The screen contrast is so much better (blacks are deeper) and we no longer get eye strain from watching in the dark.

I have hooked the bias light to an x10 controller so I can dim the light for various conditions.

My MX500 has a macro to turn on/off all the HT gear, including the bias light which adds extra wow factor - and is very convenient.

No problems with interference from the fluoro and it looks much better than the halogen desk lamp that I was previously using.

For around $50, this addition to my Home Theatre has made a huge improvement in viewing conditions.

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Ideally what you're after here is a daylight fluorescent tube with a colour temperature the same as your screen and a good CRI.

Fluorescents are rated by their colour temperature and their colour rendering index. The CRI is how close the colour temp is to the CIE "black body curve" and is given as a number, the higher the better. 100 is perfect, 90 (or .9) is pretty good. Fluoros with low CRI's produce a colour cast (e.g. they're green to the eye)

Ideally a screen is D6500, and so the bias lighting should be too. The wall the light falls on behind the screen should also be neutral, so it doesn't contribute its own colour cast.

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Oh dear ... another trip out for a further low-cost tweak! Sighhhh .....

I've been using a halogen desk lamp to light up a nearby painting for ambient lighting and it is *most* distracting! Does anyone know if Ideal Elec carries the unit that Delbz referred to as: "Crompton Slimline Linkable Fluorescent 20watt light (for about $45 from Bunnings)". Sounds perfect for me. :blink:

Cheers,

Ian

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interesting discussion, i've been dealing with the same back lighting issue again recently :blink:

i improvised previously by using small fridge lightbulbs (15 watt) that i found at bunnings, and am using 2 of those behind my crt tv, this seems to work fairly well but i havnt seen other setups to compare it to.

why do some people say that fluorescent light would be better for this use ?, dont normal lightbulbs provide better softer light versus the bright glare of fluro's ?

and are backlighting requirements different for projection screens, plasma, and CRT's ?

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This is a continuation of a discussion that started up in the SXRD Owners' Thread, recently at this post.

As for the 6500k lamp for bias lighting, if the walls are a warm colour, a colder lamp would be advisable (8000k), as the walls will greatly affect the color temperature of the light in the room. Conversely if the walls are a cold colour, a warmer colour lamp ( 5000k) would be the go.

There are a large range of cheap compact fluorescent lamps available these days with standard bayonet fittings that can be fitted in a cheap desk lamp. The lamp can be placed behind the display aiming up at the wall at the ceiling.

Normally the colour temperature is written on the box, so you can try a range of options to see what you find works best with your room colouring.

... Are you using a 6500K neon ?????

Also what size is the tube and will you try other wattage tubes. Thinking of having a fiddle with bias lighting too. ...

The fluorescent tube I used is a standard 36W tube 1200mm long, rated as 'cool white', which is generally a colour temperature in the range 4,100 - 4,200 degrees Kelvin, but in my case it is a 4,000 K tube. I've had it lying around. Cool white fluorescents may use three phosphors and may thus cover a reasonable range of colour.

The whole thing was about $25 at Bunnings, including the metal batton fitting and an attached power lead and plug. The length of the tube is convenient as it is about the width of my 60" SXRD screen, and the light emitted is nicely diffuse. The actual amount of light that reaches the room will depend a great deal on the mounting position and angle, and the nature of the wall surface the light bounces off.

After setting up the lamp (simply placing it horizontally, pointing upwards, on the back of the stand that supports my SXRD) I turned off all other lights in the room. I watched a high bit-rate demonstration 1080i video and the colours on the screen had quite a richness to them. The bias light gave a worthwhile improvement.

I am not sure that the colour temperature of the lamp is going to be all that critical. However, as Owen suggests, it may help to trial different tubes and see how they perform when illuminating whatever surface is behind (or above) the television.

A modern "wide spectrum" or "high colour rendition" fluorescent tube may give a better result. These are sometimes marketed as tri-phosphor tubes.

I am a bit concerned about the fact that a standard fluorescent tube dims 100 times a second. It might cause eye fatigue when watching a 50Hz TV picture. [Compact fluorescent devices that fit into a bayonet socket usually operate at a much higher frequency, avoiding flicker.]

Here is a para about CRI, from Wikipedia:

The Color Rendering Index (CRI) (sometimes called Color Rendition Index), is a measure of the ability of a light source to reproduce the colors of various objects being lit by the source. It is a method devised by the International Commission on Illumination (CIE). The best possible rendition of colors is specified by a CRI of one hundred, while the very poorest rendition is specified by a CRI of zero. For a source like a low-pressure sodium vapor lamp, which is monochromatic, the CRI is nearly zero, but for a source like an incandescent light bulb, which emits essentially black body radiation, it is nearly one hundred. The CRI is measured by comparing the color rendering of the test source to that of a "perfect" source which is generally a black body radiator, except for sources with color temperatures above 5000K, in which case a simulated daylight (e.g. D65) is used. For example, a standard "cool white" fluorescent lamp will have a CRI near 63. Newer "triphosphor" fluorescent lamps often claim a CRI of 80 to 90.

I don't know a lot about bias lighting. Perhaps others do.

EDIT 11am: There's a 20 page thread over at AVS, here. A colour temperature of 6500K and a CRI of around 90 or better are generally recommended, but wall colour can have an impact on colour temperature.

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All,

All TV programs are balanced to be displayed on a 6500 k screen. The colour temperature of any background light should be the same. If it is not, it will make the white, and grey appear to be the complementary colour to the light. For example if the colour temperature of the background is too low eg daylight then the screen will look too blue.

The colour rendering index is irrelevent in this case as it should ideally be reflected from a grey or white wall. CRI only becomes a problem if you are using it to illuminate a strong coloured object. Then this object will appear to change hue if it doesn't match the colour of one of the phosphors.

The amount of light will affect the viewed contrast. It should be a third of the luminance of white.

AlanH

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All,

All TV programs are balanced to be displayed on a 6500 k screen. The colour temperature of any background light should be the same. If it is not, it will make the white, and grey appear to be the complementary colour to the light. For example if the colour temperature of the background is too low eg daylight then the screen will look too blue.

The colour rendering index is irrelevent in this case as it should ideally be reflected from a grey or white wall. CRI only becomes a problem if you are using it to illuminate a strong coloured object. Then this object will appear to change hue if it doesn't match the colour of one of the phosphors.

The amount of light will affect the viewed contrast. It should be a third of the luminance of white.

AlanH

You can replace the ballast with an electronic unit that will operate the lamp at much higher frequency (impossible for the eye to detect the switching)

The conventional ballast is switching the lamp at 50hz causing flicker or strobing

The other option is to have a twin fitting as each lamp will counteract the other

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procoholic,

The fluro flashes at 100 times a second. The TV will be flashing at either 50 or 100 times a second. The TV source is very accurate and the power mains does have short term variations in frequency due to the electrical load on the generators. However the light from behind the screen should not fall on the screen in this case strobing is not a problem.

AlanH

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I eventually bought a Crompton Slimline Linkable Fluorescent 20watt light (for about $45 from Bunnings) and positioned it behind the centre speaker.

http://cromptonlighting.com/fittings/index...base_database=1

Wow - this looks good - showroom stuff. The screen contrast is so much better (blacks are deeper) and we no longer get eye strain from watching in the dark.

I have hooked the bias light to an x10 controller so I can dim the light for various conditions.

My MX500 has a macro to turn on/off all the HT gear, including the bias light which adds extra wow factor - and is very convenient.

No problems with interference from the fluoro and it looks much better than the halogen desk lamp that I was previously using.

For around $50, this addition to my Home Theatre has made a huge improvement in viewing conditions.

Hey delbz,

Can you post some pics of your set-up with the fluro light, would be really good to see some actual shot's of how it looks.

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Hey delbz,

Can you post some pics of your set-up with the fluro light, would be really good to see some actual shot's of how it looks.

I am intriuged by this "bias lighting" technique, i too would like to see some pictures of this set up and operating as it sounds like a fairly cheap addition to improve HT viewing. :blink:

Cheers,

Disco.

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This picture shows three different 1200mm fluorescent bias lights, from top to bottom as follows:-

1. 6700K ("daylight")

2. 5000K ("natural white")

3. 4000K ("cool white")

On the left you see the bias light illuminating the curtain at the back of the set.

On the right, the bias light has been placed in front of the set so that the screen shows a reflection of it.

If your browser reduces the size of the picture, moving your cursor over the picture may give you the option to increase the size of the displayed image.

[The digital camera's white level was manually set to "sunlight".]

A lot of older tubes are around 4000K, or less. Purchasing 5000K 1200mm tubes, or compact fluorescent lights, is not too difficult: many lighting shops these days stock them. However, anything higher than 5000K may not be readily available.

I think I may ultimately go for one or more CFLs (compact fluorescent lights) as these very small units that fit into a standard light socket usually incorporate a switch-mode power supply operating in the vicinity of 30,000 Hz, thus eliminating any flicker and possible eye strain. However, so far I haven't noticed any flicker or eye-strain using conventional linear fluorescent tubes for backlighting.

_________________________________

Comments on the look of the tube reflection (images on the right):

6700K is a bluer looking colour than the 5000K tube.

5000K doesn't look too bad in comparison with the screen.

4000K is obviously too warm a colour; it looks reddish in comparison with the screen.

Comments on the appearance of the curtains (images on the left):

6700K looks a bit too bright or blue [this was more apparent with the naked eye]

5000K looks dull

4000K is much too dull and warm (reddish)

Comments on the bias lights in use whilst watching the TV:

6700K - The bias light was a bit bright in its colour, except for some outdoor scenes

5000K - The bias light was somewhat dull for outdoor scenes, good for indoor scenes

4000K - The bias light looked much duller in colour than the picture

Change made to the set:

All of the above was carried out with the TV set involved, a Sony 60" SXRD rear-projection, in "power saving ON" mode. This reduced the current to the rear-projection bulb.

The setting was then changed to "power saving OFF" mode

Comments on the bias lights in use whilst watching the rearpro TV operating at a higher lamp current:

6700K - The bias light looked bright for indoor scenes and slightly dull for very bright outdoor scenes.

5000K - The bias light looked dull for bright outdoor scenes

4000K - The bias light looked much too dull for the picture

Conclusions:

For this set, and the particular curtains behind it, a 5000K tube is ok with the set operating in power saver mode, but for the set operating in normal full power mode, the 6700K tube seems better. The 4000K tube is not suitable at all as its colour is duller than even indoor scenes shown on the TV screen.

The colour of the bias tube makes a big difference as it provides a reference colour for the eye. It was quite obvious when a high definition video changed from an indoor scene to an outdoor scene that the 'colour temperature' of the picture was different. It was also possible to guess whether an outdoor scene was overcast or in full sunshine.

As is well known, the intensity of the bias light improves picture contrast by allowing near blacks to look blacker. This benefit occurred with all three tubes.

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For this set, and the particular curtains behind it, a 5000K tube is ok with the set operating in power saver mode, but for the set operating in normal full power mode, the 6700K tube seems better. The 4000K tube is not suitable at all as its colour is duller than even indoor scenes shown on the TV screen.

The colour of the bias tube makes a big difference as it provides a reference colour for the eye. It was quite obvious when a high definition video changed from an indoor scene to an outdoor scene that the 'colour temperatue' of the picture was different. It was also possible to guess whether an outdoor scene was overcast or in full sunshine.

As is well known, the intensity of the bias light improves picture contrast by allowing near blacks to look blacker. This benefit occurred with all three tubes.

Thanks MLXXX for the pics and very detailed report. I will definatly look into bias lighting when my Sony 3LCD arrives next week. Is it just a matter of trying a few different tubes and seeing which works best for the environment it will be used in?

Cheers!

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You're welcome, Disco-123.

Here's a webpage I've stumbled across that has an interesting diagram of colour temperature and spectral emission, for the scientifically inclined.

All,

All TV programs are balanced to be displayed on a 6500 k screen. The colour temperature of any background light should be the same. If it is not, it will make the white, and grey appear to be the complementary colour to the light. For example if the colour temperature of the background is too low eg daylight then the screen will look too blue.

The colour rendering index is irrelevent in this case as it should ideally be reflected from a grey or white wall. CRI only becomes a problem if you are using it to illuminate a strong coloured object. Then this object will appear to change hue if it doesn't match the colour of one of the phosphors.

The amount of light will affect the viewed contrast. It should be a third of the luminance of white.

AlanH

Hi AlanH,

There is a complelling logic to what you say about CRI. The various web references to bias lighting often mention the importance of a high CRI, but they provide no reason or it, or the particular circumstances where it might offer a benefit.

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All,

There is a difference between sunlight and daylight. Sunlight is around 4000 k and consists of the light emitted from the sun only. 6500 k is the colour of a white cloud viewed in a southerly direction around midday local time.

Illuminant D6500 is as described but also includes the effect of UV radiation on flourescent colours.

MLXXX.

A really good attempt however you need to keep the following in mind.

The camera was balanced to give white for a lower colour temperature than what is used for TV, so you came up with the result you did. If your digital camera was white balanced for Illuminant D you would have got the result that a 6500k tube and the display look identical. Colour balancing a camera involves for a particular white adjusting the sensitivity so that Red = Green = Blue = luminance. This is what the display receives and when correctly adjusted produces a light which looks identical to platinum metal heated to 6500 k.

The bias lighting colour temp of 6500k which can use a flourescent source is defined by the Society of Motion Picture and Television Engineers as the standard for the colour of the screen and the surround.

Other factors which affect the result is the colour balance adjustment of your display and to a much lesser extent the colour of white on the computer you are using now.

AlanH

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i would also be interested to see pictures of some peoples setups for these lights..

is it essentially a flourescent globe pointing upwards from behind the set?

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i would also be interested to see pictures of some peoples setups for these lights..
Me too.

But I wouldn't use flourescent globes either.

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Seoul Semiconductor Unveils Warm White Acriche of 42lm/W

Seoul Semiconductor of Korea has announced that Acriche, claimed to be the world's first semiconductor lighting source for AC power outlets, can now achieve warm white of near-daylight quality, making it suitable for general and indoor lighting applications. The warm white Acriche features 42lm/W based on light source.

Actual system efficiency -- which takes into account luminous efficacy, ballast efficiency and luminaire efficiency -- for the warm white Acriche is 39.9lm/W. This is higher than 7.5lm/W for incandescent lamps and 30.6lm/W for compact fluorescents.

Warm white Acriche is a suitable replacement for DC-LED lighting. Compared to conventional warm white DC LED which has a luminous efficacy of nearly 35 lm/W, the warm white Acriche at 42 lm/W is 20% more efficient. Warm white Acriche can also produce a brighter lighting environment without the need of a converter or ballast.

The company has also released warm white Acriche with a luminous efficacy of 33lm/W which has a color rendering index (CRI) rating of 90. The CRI measures the ability of a light source to produce vibrant colors in objects. A CRI rating of 100 suggests that the light source is equivalent to daylight, while a low CRI rating near 0 suggests that colors will appear unnatural under that particular light source.

Acriche warm white's high CRI ratings and superior color rendering capabilities make it a suitable solution for environments that demand vibrant and accurate lighting, such as museums, luxury hotels, art galleries, show rooms and displays.

For many years, the ability to produce a warm white semiconductor lighting source that can also offer a high quality CRI rating had appeared illusive. Today, that hurdle has been successfully negotiated.

http://techon.nikkeibp.co.jp/english/NEWS_...0070424/131506/

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Seoul Semiconductor Unveils Warm White Acriche of 42lm/W

Interesting article.

Warm white would be around 3000K. Coventional wisdom would recommend something closer to the television standard of 6500K (cool white).

i would also be interested to see pictures of some peoples setups for these lights..

is it essentially a flourescent globe pointing upwards from behind the set?

Some people use a bracket attached to the back of their set to support a horizontal fluorescent tube. I don't think it's necessary the bias light illuminate the area behind (and above, below, and to the sides of) the set with complete evenness.

The AVS site I referred to at post #9 mentions strip lighting or rope lighting placed behind the screen along its edges.

Bias lighting is useful for:

  • Establishing a reference intensity so that blacks in the picture do look dark enough, in comparison, to be interpreted by the human eye as black. This is particularly important with displays that have a limited contrast range and display black as a darkish grey.
  • Reducing eye-strain resulting from the iris of the human eye dilating during prolonged dim scenes (in a dimly lit viewing room) and then being subjected to a bright scene. (I find this important with my SXRD rear-pro, which has a high contrast ratio.) The bias light stops the human iris from dilating excessively.
  • Establishing a reference colour for white. (In my opinion, this can be helpful when watching a movie as it helps the viewer to appreciate the the time of day, or weather conditions, when a scene was shot. An overcast day in London looks very different to a sunny beach in the Carribean.)

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I just use one table lamp on one side left of screen and a pedestal lamp on the right of the room (both behind the plasma screen & both rated at 25w) works well for me.

I wouldn't use flouro's mainly because they change light spectrum/colours in the room also have bad experiences of rf interference from them in my system.

I see the new range of philips lcd/plasma come with a built in backlight.

Al is the pedestal lamp you speak of the one that can be seen here.

Diva_in_place_resize.JPG

Or is it hidden from view?

Lyle

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I eventually bought a Crompton Slimline Linkable Fluorescent 20watt light (for about $45 from Bunnings) and positioned it behind the centre speaker.

http://cromptonlighting.com/fittings/index...base_database=1

Wow - this looks good - showroom stuff. The screen contrast is so much better (blacks are deeper) and we no longer get eye strain from watching in the dark.

I have hooked the bias light to an x10 controller so I can dim the light for various conditions.

My MX500 has a macro to turn on/off all the HT gear, including the bias light which adds extra wow factor - and is very convenient.

No problems with interference from the fluoro and it looks much better than the halogen desk lamp that I was previously using.

For around $50, this addition to my Home Theatre has made a huge improvement in viewing conditions.

I followed this advice last year and I'm really happy with the result - the fluro is powered from the back of the AV receiver, and I used a little kitchen Alfoil to direct the light to my satisfaction.

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If you have white walls or offwhite I have a cheap solution which works a treat. ( I actually think I got the solution from a post by Owen some years back in a similar thread. )

I have an NEC 50" approx 60cm/2ft from the corner. Nipped to KMart bought a cheap table lamp stand approx 40cm tall and a Philips Genie 11w cool daylight globe. All in less than $30.00. Placed the lamp directly behind the screen in the centre. It lights up the back wall, ceiling and corner without any direct light falling on the screen in fact just like Ambilight. I can't see any flicker or any thing from this small flouro.

Only drawback is nightime flying insects are attracted to the daylight globe. I collect a small pile of tiny dead critters from behind the TV.

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