Results 1 to 15 of 15

Thread: LED vs. LCD Blue Light Transmittance

  1. #1
    Master OptiBoarder
    Join Date
    Jul 2012
    Location
    Houston, Texas
    Occupation
    Other Eyecare-Related Field
    Posts
    450

    LED vs. LCD Blue Light Transmittance

    A segue from another thread: I know that LCD screens generate a degree of blue light, but where does it stand in comparison to LEDs? It seems that LEDs are getting all of the attention (justifiably, especially with the dawn of LED lightbulbs), and I know that LCDs emit enough to fiddle with circadian rhythms, but does it pose nearly the hazard that LEDs do? Does anyone have any hard data on LCD frequency vs. LED?

  2. #2
    Manuf. Lens Surface Treatments
    Join Date
    Aug 2002
    Location
    in Naples FL for the Winter months
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    23,240
    LED is short for light emitting diode. It is the simplest semiconductor device having only two junctions. A transistor is another semiconductor device but with three junctions. Heat is released when a current passes through an ordinary diode. The heat is released when an electron jumps from one energy gap to another. For a LED, that heat is converted to light. A LED bulb can be of several colors depending on the material used.

  3. #3
    Master OptiBoarder
    Join Date
    Jun 2008
    Location
    Seattle WA
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    3,137
    The lifetime amount of Blue Light emitted by any portable device or TV is minuscule compared to only a short exposure to sunlight.

  4. #4
    Master OptiBoarder
    Join Date
    Feb 2008
    Location
    Jacksonville, Florida
    Occupation
    Optical Laboratory Technician
    Posts
    1,012
    LCD (liquid crystal display) is a display technology
    LED (light emitting diode) is an illumination technology
    Clinton Tower

    The intellect to live free is in short supply
    ALT248=°

  5. #5
    Master OptiBoarder
    Join Date
    Jul 2012
    Location
    Houston, Texas
    Occupation
    Other Eyecare-Related Field
    Posts
    450
    This article indicates a HEV hazard risk from LCDs. Is it BS?

  6. #6
    Banned
    Join Date
    Jun 2014
    Location
    toronto
    Occupation
    Other Eyecare-Related Field
    Posts
    1
    @Browman: Hi, I think the Led displays are better than the LCD displays because LCD displays uses fluorescent lights and that is why it emits more blue light and on the other hand LED displays uses the LED lights so no such issue with LED lights.

  7. #7
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    2,918
    Quote Originally Posted by sharpstick777 View Post
    The lifetime amount of Blue Light emitted by any portable device or TV is minuscule compared to only a short exposure to sunlight.
    Precisely.

    Quote Originally Posted by scriptfiller View Post
    LCD (liquid crystal display) is a display technology
    LED (light emitting diode) is an illumination technology
    There is a break down here in understanding of terminology (You said it perfectly however). LED is a light emitting diode - ie: a type of light bulb. And LCD is a liquid crystal display. It does not emit light by itself. It is always backlit from an independent light source. This can be fluorescent, LED, OLED or some other technology.

    Strangely, I would love to see the data on the massive increase in cataracts and mac degen cases when humans made the switch from candles, campfires and gas lights to the much more blue transmitting incandescent and then halogen light sources. Anyone?


  8. #8
    Chemistrie Eyewear
    Join Date
    Aug 2012
    Location
    Pennsylvania
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    152
    Quote Originally Posted by Uilleann View Post
    Precisely.


    Strangely, I would love to see the data on the massive increase in cataracts and mac degen cases when humans made the switch from candles, campfires and gas lights to the much more blue transmitting incandescent and then halogen light sources. Anyone?

    Actually incandescent and halogen lights produce proportionately less blue light compared to most other light sources. See the charts on page 5 in this presentation which show the spectrum emitted from common light sources:

    http://www.crizalusa.com/SiteCollect...te%20Paper.pdf

  9. #9
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    2,918
    Quote Originally Posted by Joe Zewe View Post
    Actually incandescent and halogen lights produce proportionately less blue light compared to most other light sources. See the charts on page 5 in this presentation which show the spectrum emitted from common light sources:

    http://www.crizalusa.com/SiteCollect...te%20Paper.pdf
    Their chart looks highly suspect at best. No mention of the brand, intensity, or even the reported color temp of the various bulbs they claim to have mapped there. Further, there is zero mention of the final transmission plots of various light sources, as viewed by the human eye on the other side of an [LCD or other] screen. That obviously will change things even more. :) But of course, who needs peer reviewed data in a round table discussion presented to push a particular new product? Blatant bad form by Essilor on this one.

    Of course, according to their charts there, our eyeballs should all but explode the instant we step outside...and I have only seen that happen once or twice over the years. -And only in the movies. ;)


  10. #10
    Bad address email on file
    Join Date
    Dec 2013
    Location
    Bristol
    Occupation
    Dispensing Optician
    Posts
    268
    Quote Originally Posted by sharpstick777 View Post
    The lifetime amount of Blue Light emitted by any portable device or TV is minuscule compared to only a short exposure to sunlight.
    I wish the rest of the optical world would cotton on to this EXTREMELY simple point.

  11. #11
    Master OptiBoarder MakeOptics's Avatar
    Join Date
    Aug 2011
    Location
    none
    Occupation
    Other Eyecare-Related Field
    Posts
    1,327
    What makes LEDs so efficient is they emit a very specific wavelength with a sharp rise and drop in the spectrum both before and after that specific wavelength. This means if you have a RED LED the light emitted will be in the red wavelength with very little infrared and very little orange light being emitted.

    LED TV's use tricolor LED's consisting of a red green and blue channel, the combination of these colors can be used to create other colors so a pixel or LED can have any color but the makeup will be a combination of the active states of LEDs that comprise that particular color. For purple Red = Active, Green = Inactive, and Blue = Active. This is the makeup of the color purple. To control the intensity or different shades of the color purple the different diodes will be activated to different intensities so a light purple might have Red = 50% * Active, Green = Inactive, and Blue = 50% * Active which would give the same purple but dimmer. Since all LED model TV's are digital devices and digital is controlled by on off states of 1's and 0's to get the intensity to 0.5 or 50% is not directly possible digitally. That's where a microchip and crystal comes into play, the crystal or resonator creates a sort of on off cycle by resonating at a specific frequency measures in hertz (fractions of a time interval, seconds). Lets say for simplicity the crystal is 2 hertz (purely theoretical for this example) then the LED being wired to this crystal will cycle twice per second, which means in a second you could turn it on for 1/2 a second and turn it off for 1/2 a second. In essence now you have created a scenario where the state can be on for 50% of a second, creating the illusion of a half dim bulb, in reality the bulb is light full on for 1/2 a second and full off for 1/2 a second. The human eye has a thing called persistence of vision, think of a flip book where the same image is presented slightly different on each page of a book by flipping through the pages of the book you can attain the effect of motion. The brain perceives a dimmer bulb by flicking the LED on and off fast enough that the bulb looks dim, which allows a digital processor to control the working of the TV. That very same persistence of vision is why a 120hz TV is better for movies or sports that have a lot of motion since the refresh rate of the entire image on the TV screen is redrawn more times in that second, going back to our flip book example the pages are flipped faster so the animation looks smooth rather than jerky.

    That's the background, now the backlighting that was mentioned in a previous post will give you a better idea of the amount of blue light being emitted. A backlight is going to be on while the TV is on and it effects the entire screen. Overlaid on the backlight is crossed polarized filters with a liquid crystal layer between the crossed polarized layers. The liquid crystal layer controls the absorption of the backlighting and the rays that make it through the first polarized layer are polarized in one direction (assume vertically for a minute) that vertically polarized light then passes through the liquid crystal layer and depending on it's states changes polarized orientation slightly (this of the LC layer as a wave retarder) as the phase is changed these rays must then pass through the second polarized layer before reaching the watchers eye. If the LC layer does not change the phase of the light then depending on the efficiency of the polarized layers (100% efficiency is assumed) no light passes through since the light will not go through a crossed polarized set of filters that are 100% efficient. If the phase is changed 90 degrees then all of the light passes through, so the eye sees the backlight color. For simplicity backlights are white so the crossed polar states means you see black at that point of no light escapes, 90 degree phase change means you see white.

    With this background knowledge you can make some guesses as to the effects of LED vs LCD. Depending on the efficiency of the polarized filters LCD TV's are going to emit more light (assuming less that 100% polarized efficiency which is reality). Since white light is composed of the various wavelengths then yes more blue light is going to get out but that does not necessarily mean that more blue light is emitted from a LCD TV vs an LED TV. A whole lot is going to ride on the quality of the components used in both models. Go to your local TV outlet and look at a number of TV's with the same parameters and you will notice some screens are more dimly light then others. Plus the components inside like resistors that are often used to limit the current going through an LED or backlight have tolerances with the loosest being 10% variation and the best being used to power critical applications less than 1% (good luck finding one in any TV set), meaning even in the same exact model you will get some range.

    To summarize all that "who cares" they are roughly equivalent given that one creates the specific colors and the other creates white and subtracts away the wavelengths not used. In essence unless you measure the intensity of light or brightness of the screen all the theoretical nonsense is just nonsense.

    PS - don't stare at either TV with a big blue screen.
    PPS - don't stare directly into the sun.
    PPPS - always wear your visor when welding.
    http://www.opticians.cc

    Creator of the industries 1st HTML5 Browser based tracer software.
    Creator of the industries 1st Mac tracer software.
    Creator of the industries 1st Linux tracer software.

  12. #12
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    2,918
    Our TV at home (an older LED/LCD model), uses a full array LED back light source that incorporates local dimming, and not an edge illuminated style as is more common with (particularly early generations of) fluorescent and LED lit screens. Plasma and OLED technology were surprisingly absent from the above referenced study, to say nothing of the manufacturer of the screens that were measured, and their inherent color bias. In any case, the illumination intensity of a given screen will vary even further with a screen that uses local dimming, as opposed to edge lit designs.

    In short, the above referenced charts leave out so much information as to be functionally unusable.

  13. #13
    Rising Star
    Join Date
    Jan 2014
    Location
    Minneapolis
    Occupation
    Optical Wholesale Lab (other positions)
    Posts
    72
    Quote Originally Posted by sharpstick777 View Post
    The lifetime amount of Blue Light emitted by any portable device or TV is minuscule compared to only a short exposure to sunlight.
    I was looking for some research to try and look into this claim, do you have anything you could point me to? Thanks ahead of time.

  14. #14
    Eyes eastward... Uilleann's Avatar
    Join Date
    Jan 2007
    Location
    Utah
    Occupation
    Dispensing Optician
    Posts
    2,918
    Essilor's own paper states this categorically. But again, their "data" presented is beyond suspect.

  15. #15
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    I was looking for some research to try and look into this claim, do you have anything you could point me to?
    A typical LCD computer monitor produces a brightness of about 250 cd/m2. The sky at midday produces a brightness of 8,000 cd/m2, or 32 times as bright. The disk of the sun can be thousands of times as bright.

    Best regards,
    Darryl
    Darryl J. Meister, ABOM

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Transmittance of light on the ophthalmic lenses
    By shkelzen_kapllani in forum Ophthalmic Optics
    Replies: 1
    Last Post: 06-09-2010, 12:54 PM
  2. Blue Light and Macular Degeneration
    By Chris Ryser in forum General Optics and Eyecare Discussion Forum
    Replies: 5
    Last Post: 05-05-2009, 02:49 AM
  3. Blue Light Blocking Patent issued 21 years later
    By Chris Ryser in forum General Optics and Eyecare Discussion Forum
    Replies: 2
    Last Post: 04-19-2009, 04:07 PM
  4. Simple Blue light considered dangerous.........................
    By Chris Ryser in forum General Optics and Eyecare Discussion Forum
    Replies: 25
    Last Post: 12-18-2008, 09:00 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •