**broken link removed**
Older GaAs deep Red LEDS require less voltage 1.4 as the colour wavelength of the LED determines the diode threshold voltage. (IR is around 1.2, Blue or White is 2.6V (dim) and 3V bright and higher from series resistance.
If you use low Vce sat transistors from Diodes Inc(Zetex) for T3 then you can get close to doubling the battery voltage to pulse the LED voltage thru C2.
The ESR of the 5mm LED is around 15 Ohms at 20mA and increases for lower current. This ESR * C2 will determine the Pulse ON time, while R3C1 time to reach 0.6V determines the OFF time interval.