# blue v. red in alarm clocks **URL:** \ **Category:** Factual Questions\ **Created:** [June 16, 2004, 5:06pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688 "2004-06-16T17:06:03Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Trunk](https://avatars.discourse-cdn.com/v4/letter/t/87869e/32.png) [@Trunk](https://boards.straightdope.com/u/Trunk)\ **Post date:** [June 16, 2004, 5:06pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/1 "2004-06-16T17:06:03Z")
Why do some alarm clocks have a blue display and some have a red display? The blue seems irridescent to me. I may not be using that word right. The blue actually gives off light. The red just seems to be lit red but doesn’t really glow outside of its display. Is there something about the properties of blue light and red light that makes blue project more? Is it just marketing? (people seem to like the blue!) At least to my eyes, the red even pierces through ambient light better. What’s going on here? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 16, 2004, 5:11pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/2 "2004-06-16T17:11:37Z")
Of course it’s marketing. They’ve had blue LED clocks for some time now. If people weren’t buying them, they’d have stopped making them. As to why the blue looks brighter, it’s in part because your eye is more sensitive to blue light than it is to red. There are also green LED clocks. Some people find these more comfortable to look at than either red or blue. ---
**Author:** ![Trunk](https://avatars.discourse-cdn.com/v4/letter/t/87869e/32.png) [@Trunk](https://boards.straightdope.com/u/Trunk)\ **Post date:** [June 16, 2004, 5:18pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/3 "2004-06-16T17:18:41Z")
> [@Q.E.D.](#): > > If people weren’t buying them, they’d have stopped making them. There seems to be a “confounding factor” there for their research numbers because I notice a lot of models only seem to come in one color. That is, last time I shopped around, I expected to see a Sony “Dream Machine” in red and blue, side-by-side on the shelf. That wasn’t the case though. Each model seem to exclusively be either red or blue. ---
**Author:** ![umop\_ap\_sdn](https://avatars.discourse-cdn.com/v4/letter/u/dbc845/32.png) [@umop\_ap\_sdn](https://boards.straightdope.com/u/umop_ap_sdn)\ **Post date:** [June 16, 2004, 9:27pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/4 "2004-06-16T21:27:12Z")
> [@Q.E.D.](#): > > As to why the blue looks brighter, it’s in part because your eye is more sensitive to blue light than it is to red. Nitpick: that’s only true at night when people depend on the rod cells in their eyes. Rods are quite good at picking up blue, but don’t detect red very well at all. Under the garish lighting inside a store, where cone cells are active, the red will look brighter. Also, since spatial resolution is in the cones, a red display is easier to read. Blue LEDs do look really cool, however. 😃 ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 16, 2004, 10:45pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/5 "2004-06-16T22:45:32Z")
If we’re talking about radio-type alarm clocks (mains powered) of the type that have been around a while, then the blue and the red displays are fundamentally different technologies; the red one is usually implemented with 7-segment LED displays, whereas the bluish (greenish) one uses a Vacuum Fluorescent Display. ---
**Author:** ![dnooman](https://avatars.discourse-cdn.com/v4/letter/d/839c29/32.png) [@dnooman](https://boards.straightdope.com/u/dnooman)\ **Post date:** [June 16, 2004, 11:30pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/6 "2004-06-16T23:30:06Z")
My Nakamichi radio alarm has a green diplay, and has automatic brightness adjustment according to available light. I got the thing in '88 and it still works like a champ. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 16, 2004, 11:48pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/7 "2004-06-16T23:48:49Z")
> [@Mangetout](#): > > If we’re talking about radio-type alarm clocks (mains powered) of the type that have been around a while, then the blue and the red displays are fundamentally different technologies; the red one is usually implemented with 7-segment LED displays, whereas the bluish (greenish) one uses a Vacuum Fluorescent Display. This isn’t true anymore. With the prevalence of inexpensive blue LEDs nowadays, most blue digital displays are now LED, not VF. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [June 17, 2004, 12:16am UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/8 "2004-06-17T00:16:47Z")
I have a friend who is partially blind. Once, when helping her shop, she was looking for a clock, and mentioned that she had a very had time seeing the red led ones, and had to look for something in the green or blue range. Back then, those were pretty rare. Now, they are fairly common. So one reason for the different colors in displays may be to accomodate people with vision problems, color-blindness, etc. ---
**Author:** ![Fish](https://avatars.discourse-cdn.com/v4/letter/f/bc8723/32.png) [@Fish](https://boards.straightdope.com/u/Fish)\ **Post date:** [June 17, 2004, 12:46am UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/9 "2004-06-17T00:46:16Z")
The red clocks are positioned at one end of a box canyon on an alien planet, and the blue clocks are positioned at the other end of the box canyon… ---
**Author:** ![Tess\_of\_the\_Derbyville](https://avatars.discourse-cdn.com/v4/letter/t/8dc957/32.png) [@Tess\_of\_the\_Derbyville](https://boards.straightdope.com/u/Tess_of_the_Derbyville)\ **Post date:** [June 17, 2004, 2:15am UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/10 "2004-06-17T02:15:08Z")
I always use the blue ones because I’m red-green colorblind (yep, I’m a girl) and the red numbers on black are invisible to me in a brightly lit room. For years I thought they just didn’t work during the daytime. Now if I could only find a blue clock with giant numbers. (I’m nearsighted too) ---
**Author:** ![Logitech](https://avatars.discourse-cdn.com/v4/letter/l/e19b73/32.png) [@Logitech](https://boards.straightdope.com/u/Logitech)\ **Post date:** [June 17, 2004, 3:04am UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/11 "2004-06-17T03:04:47Z")
> [@Trunk](#): > > The blue seems irridescent to me. I may not be using that word right. The blue actually gives off light. The red just seems to be lit red but doesn’t really glow outside of its display. Not true, I’ve got a red alarm clock with two inch high letters, and even in its dimmed position, it lights up my room at night, not quite enough to see by, but enough to see the reflection off the book case, chair and desk. ---
**Author:** ![Trunk](https://avatars.discourse-cdn.com/v4/letter/t/87869e/32.png) [@Trunk](https://boards.straightdope.com/u/Trunk)\ **Post date:** [June 17, 2004, 11:38am UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/12 "2004-06-17T11:38:35Z")
> [@Tess of the Derbyville](#): > > I always use the blue ones because I’m red-green colorblind (yep, I’m a girl) and the red numbers on black are invisible to me in a brightly lit room. For years I thought they just didn’t work during the daytime. Now if I could only find a blue clock with giant numbers. (I’m nearsighted too) [here ya go.](http://www.walgreens.com/store/product.jhtml?id=prod392147&CATID=100408&skuid=sku392148&V=G&ext=frgl_701937) That’s part of my problem too. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 17, 2004, 3:00pm UTC](https://boards.straightdope.com/t/blue-v-red-in-alarm-clocks/250688/13 "2004-06-17T15:00:37Z")
> [@Q.E.D.](#): > > This isn’t true anymore. With the prevalence of inexpensive blue LEDs nowadays, most blue digital displays are now LED, not VF. Which is why I said ‘of the type that have been around a while’ - I got the impression that the OP was talking about things having \*always been’ this way (although this is entirely my assumption).