Electronics > Projects, Designs, and Technical Stuff

Ultra Short, Ultra Fast LED Flash

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Marco:
Looking around the web I'd guestimate a LED spotlight overdriven to 100W will do about 100K Candela. So to achieve the same intensity as the Microflash you'd need about 50kW of overdriven power.

JAndrew:

--- Quote from: Marco on March 09, 2019, 05:43:14 pm ---Looking around the web I'd guestimate a LED spotlight overdriven to 100W will do about 100K Candela. So to achieve the same intensity as the Microflash you'd need about 50kW of overdriven power.

--- End quote ---


Hmmmm, my first impression is that that’s beginning to touch on the realm of  impractical.


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dmendesf:
You need to use an Arduino timer to drive the pulse (probably in pwm mode, but I'm not sure... I know pics better than avr). This  way you will have very fine control of the pulse width (with steps of 1/f, so about a hundred ns).

Enviado de meu moto g(6) plus usando o Tapatalk

NiHaoMike:
Some modern xenon flashes use IGBTs to allow switching off the tube at an arbitrary time. 500ns is definitely on the fast side for IGBTs, but maybe it can be done with MOSFETs? Apparently, using a higher voltage but lower capacitance also helps for shortening the duration of xenon flashes.

Where LEDs excel is for video lighting in order to reduce motion blur, where the operating frequency is much too high for xenon. Unfortunately, few consumer/prosumer cameras have a sync output, but maybe it could be possible to use the vsync from the HDMI output, then use an adjustable delay circuit to sync the LEDs to exactly the right time?

JAndrew:
This is the unit we used to take the pictures.

http://prismscience.com/spot.php

Taken Directly from the specification page.

SPOT: Specifications
Housed in a 6.7" H 6.7 H 8" enclosure (Fig 1), and weighing in at 10 lbs, SPOT is a compact submicrosecond flash system operating from 120 VAC power. Three trigger inputs are included:
· Manual — push button
· Switch closure — �" phone jack
· Pulse (e.g. TTL) — BNC
The stored energy of approximately 8 J is released in a short flash of less than 500 ns. Fig. 2 illustrates FWHM and FW1/3M times for full visible spectrum and for 520 nm line filter. The light collected by a 6" fresnel lens forms a relatively uniform "spot, " Fig. 3. The peak intensity of 69 million lumens delivers a pulse having 28.5 beam candlepower-seconds. At 40" from SPOT, the beam diameter is nominally 20" to 24"; however, beam spreads from 14" to 40" can selected during manufacture. A typical camera setting is f/5.6 to f/8 at 200 ASA for objects illuminated from 3 feet.

The design can be adapted to create different output characteristics for specific applications, such as a 2.7 J pulse with 200 ns FWHM for extremely fast motion, or point sources for shadowgraphs or schlieren images.

I'm referencing this as a comparison for what I'd like to try an emulate.  The one point I see that I hadnt looked at before was the lumens 69Mil. Trying to drive that sort of output from LED's even if it is for a brief period doesn't seem feasible.

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