Chris B wrote:LED brightness is controlled by current, not voltage. And after the LED gets to "full" brightness, more current has little impact. Until the magic smoke escapes.Chris
You are right Chris. I was trying to keep it simple. (I should have known better with all of the sharp eyes on DAN.) As it sounds like you know, the threshold at the junction of common LEDs is seldom above a few volts. Current does determine luminosity but still only within a relatively narrow range above the threshold (avalanche) voltage. Internal voltage regulation circuitry (generally not resistors except in the simplest of circuits for reasons that you understand) either hold current constant (non-dimmable LEDs) or adjust how much current the LED is allowed to draw as a function of the input voltage (dimmable LEDs). Even this simplifies things a bit. These days, virtually all but the 10 for $1.00 pigtail LEDs contain internal regulation circuitry. I jut purchased a couple dozen 5 watt, 500 lumen CREs to replace the 60 watt tungsten reflectors I have running around the outside perimeter of my house. These bulbs (non-dimmable) produce constant rated output with input voltages rated from 80 to 260 VAC.
I think you made the key point here in an earlier post. The dimming circuitry on our aircraft was probably designed for a tungsten load where the resistance decreases as the tungsten cools. These bulbs can be dimmed with simple, comparatively reliable circuitry. Not so much so with LEDs. Many more components. More links in the failure chain.
CFIDave wrote:One more important note (taken from the Canadian L360 DA42 parts list):
NOTE: If this LED lamp is installed, the same P/N LED lamp must be installed in all four places on the Landing Gear Panel. Mixing of bulbs and LEDs are not permitted.
I imagine that this same note would also apply to the flap bulbs on either the DA40 or DA42, i.e., don't mix bulbs.
I wrote to tech support at Diamond Canada about the fact that a LED replacement is approved in other DA42's but not the Thielert planes, and here is the response I received:
Hi Cary, I have been advised that we only installed LDG/Flap LED indication in a few DA42NG (VI) aircraft and no longer do so. The LED was found to be too bright. The on line IPC has removed the LE as an alternative for the flap indication and I suspect in the next revision may remove the LED for the LDG indication. The current LED part number from the IPC we stock under 461K022801WS. Let us know if you have any questions.
Frank Lemaire
Customer Support,
Technical Services Specialist
So, it seems that for all the DA42's we will still need to use the incadescent bulbs rather than LED's. I bought a box of 10 for about $20, and will continue to replace with these as needed.
This is not for everyone but I have found a number of special purpose LEDs via this aggregation site, which brokers deals directly with the Chinese factories and distributors that actually make the stuff we purchase from US firms, typically after additional layers of commerce. http://www.dhgate.com/ Orders can arrive in 10 days or 45 days . . . no particular rhyme or reason but the merchandise has always arrived. The actual products I have purchased are high quality.
CFIDave wrote:Here is the LED bulb info again for anyone who wants to order it.
The Diamond part number: 461K_02_2801_WS (Single-LED T4.6-28V/1mA white)
The LEDs list for about $18 apiece vs. about $5 for the older incandescent bulbs.
I asked our shop to replace our incandescent flap indicators with these. When he tried to order them, the following response came back from Diamond:
Diamond Support wrote:Hi, for the DA40-180 only the T4.6 24-20 incandescent bulbs are certified for the flap indication lights. Let me know if you have any questions.
Where did you buy your spare bulbs. I am going to check the dimmer on Saturday, but seems the up flaps light is the only one out and others are bright as ever. Thanks
dwurfel wrote:Where did you buy your spare bulbs. I am going to check the dimmer on Saturday, but seems the up flaps light is the only one out and others are bright as ever. Thanks
You can find them at many places on the internet. You can buy 10 of the for $15 here:
I was able to use these tweezers to pull the lamp. Removal/reinstall of the lens and lamp was best done by hand/finger/fingernail. Lamp and lens both click clearly into place when installed properly.
Ok, so last month I ordered and received 15 replacement bulbs for $15.00 from Atlanta Light Bulbs and used one to replace the single bulb that had burned out. Essentially I now have a lifetime supply of these things. So forevermore I get emails reminding me that I now have a $0.15 credit for my next purchase